GEOLOGICAL SURVEY OF GEORGIA W. S. YEATES, State Geologist BULLETIN NO. 6-A A PRELIMINARY REPORT ON A PART OF THE CLAYS OF GEORGIA BY GEO. E. LADD Assistant Geologist 1898 GEO. W. HARRISON, STATE PRINTER FRANKLIN PRINTING AND PUBLISHING COMPANY Atlanta, Georgia THE ADVISORY BOARD of the Geological Survey of Georgia ( Ex-Officio) H1s ExcELLEt-:CY, \V. Y. ATKINSON, Governor of Georgia, PRESIDEXT oF THE BoARD Ho"'. R. T. NESBITT ______________ Commissioner of Agriculture IIoi>i. G. R. GLENN_. ___ Commissioner of Public Schools Hox. \V. J. SPEER ______________________ State Treasurer Hox. \V. A. WRIGHT. ___________ .. ____ Comptroller-General Hu"'. WILLIAJ\I CLIFTOI\ ____________ _ Secretary of State Hox. J. l\I. TERRELL ___________________ ;\ttorney-Gcncral October 4th, rSgS. To !lis r_x!'L'!klli)'. \\'. Y. i\TKrxso:-;, Gocrnor, and Prtsidcnt of t!tc .ldi.'ZSOJY noani of tiLe c;to!o,:;iml Sur<'()' of GcOI::;ia: - Sat:-- I han: the honor, to transmit, herewith, the report of Dr. Geo. E. Lade!, formerly an 1\ssistant Geologist on this Survey, on a part of Trr r-: CL\ Ys oF G I:cmcL\. ; \s stated in my 1\dministrati ve Report for ISC);, the first part of the report, which had been furnished the State Printer, was withdrawn by Dr. Lade!, in ~Iarch, r Sg 7, to add new matter. He resigned his position the follo\Ying October, without finishing the report; and I am just in receipt of the last pages, \\hich complete it. The subject is one of \Try great economic importance to the State; and I trust the report \Yill meet, in part, at least, the many requests for information about the clays of Georgia, \Yhich I ha\-e received from imestors, in the North and \\'est. Field-\York ,,ill be continued on this subject, at the earliest time possible; and the second bulletin uf the series, \Yhich shall cover more territory, \\ill be published. \'cr: respectfully yours, \\'. S. YK\TES, State Geologist. THE CLAYS OF GEORGIA CHAPTER I GENERAL REMARKS ON CLAYS Clays and clay industries may be conveniently discussed, from scientific, industrial or historical standpoints. Scientific considerations deal with the definition and classification of clays; their geological occurrence and distribution; their geographical distribution; their chemical and physical composition and structure; their origin and properties; and the composition, structure and properties of clay-products. Industrial considerations are those, dealing, specifically, with the manufacture of clay-wares, for all the various uses, such as structures (buildings, roads etc.), ornaments (architectural pieces and art-pottery), fire-proofing, heat and electricity insulating, utensils (pottery and porcelain), sewer-pipes, drain-tiles and miscellaneous products; also, with the use, or misuse, of clay, as an adulterant (for paints, foods etc.). They, further, deal with the methods of mining and preparing clays, and with the statistics, connected with all these subjects. Historical considerations are those, dealing with the history of (7) 8 DISCUSSION OF THE PROPERTIES OF CLAYS the manufacture of clay-products, and with the development of our knowledge of clays. Clay articles are among the earliest manufactured products of primitive man; and fragm~nts of clay utensils are among the most enduring records of mari's existence. The most ancient historical records refer to the art of pottery-making, as being then in an ad~ vanced stage. The Chinese claim, that glazed pottery was invented, by an Emperor, called H wang-to;, whose "legendary reign, of a hundred years, is said to have commenced in the year 2,697, B.C." It is claimed, that the potter's-wheel was known to the Egyptians, as early as 2,5.00 years, B. C.; and that a sort of porcelain was manufactured by them, during the Sixth Egyptian Dynasty, which is stated, by some authors, to have been as early as 3,700, B. C. From these early beginnings, the use of clay has gradually expanded, increasing rapidly, since the discovery of the art of making porcelain, by the Chine5e, at about the beginning of the Christian era; and, again, enormously, on the introduction of porcelain into Europe; and still more emphatically, since the art of making white porcelain was discovered by the Europeans, at the beginning of the Eighteenth century. At the present time, the uses, to which clay is put, have become so varied, and its application. to many of these uses, so universal, that this has been called, not unjustly, the "Age of Clay", as well as the "Age of Steel". In spite of the varied application of clays to the technical and fine arts, ranging all the way, in result, from the coarsest common brick to the most exquisite pieces of art istic pottery, there has been ah extraordinarily small amount of scientific research, concerning their nature and properties. What has been done, has b~en achieved largely by the Germans; though, at present, the importance of the pa DISCUSSION OF THE PROPERTIES OF CLAYS 9 subject is becoming recognized; and the Americans, English, French, Swedes and Russians are beginning to turn their attention to these scientific investigations. In this country, recognition of the subject is illustrated, by the number of States, which have finished, or are at present undertaking, the preparation of treatises on the occurrence, distribution, origin, nature, uses etc. of the clays, within their boundaries. Among these, are the States of New York, New Jersey, Maryland, Ohio, Kentucky, Iowa, Missouri, Indiana, California, Arkansas, Texas, Alabama and Georgia. The reports of some are already published. Those of others are in print, and the rest are unfinished, awaiting the completion of field-work. DEFIXI1'IOX AND CLASSIFICATION The term clay is a generic name, for a group of more or less consolidated secondary rocks, \vhich are composed of hydrous silicates of aluminum, usually associated with other minerals (present as impurities), which originate, chemically, as products, after the decomposition of various aluminum-bearing minerals, chiefly feldspar, and which occur, either at the place of their origin, from the maternal rock, or removed thence by geologic agencies, in foreign localities. Clays arc commonly classified, from a commercial standpoint, with reference, especially, to the uses, for which particular clays are adaptable. From a geological standpoint, the writer suggests, that they be classified into larger divisions, based on origin and mode of occurrence; and into minor subdivisions, according to 10 DISCUSSION OF THE PROPERTIES OF CLAYS their composition and properties. The larger divisions of such a classification would be somewhat as follows: - CLASSIFICATION OF CLAYS INDIGENOUS. A. Kaolins. a. Superficial sheets. b. Pockets. c. Veins. FOREIGN OR TRANSPORTED.- A. Sedimentary. a. Marine. I. Pelagic. 2. Littoral. b. Lacustrine. c. Stream. I. Flood-plain. 2. Delta. B. Meta-sedimentary. c. Residual. D. Unassorted. In this classification, the INDIGENOUS CLAYS, as the term implies, includes all those varieties, commonly called kaolin, which occur in situ, or in the immediate place of their origin, where feldspars or other aluminous silicates have been decomposed, and, in part, chemically reconstructed into clays. These are commonly called, by geologists, "residual clays", with the meaning, that they are left behind, upon the decomposition of the parent rock. But the process, completed, is one of reconstruction, and a greater percentage of the altering material remains, than is removed in solution. Further, as DISCU.'>~VON OF THE !'ROPER TIES OF CL4 YS I I there are other clay occurrences, which are more properly "residual", in the meaning of the word, the term has been reserved for its apparently more proper use. THE FOREIGN or TRANSPORTED CLAYS include all those, which have been moved, by aqueous or aerial agencies, to points, more or less remote, from the place of their chemical origin. This group of clays differs, among its members, in the manner of their occurrence, and the history of their migration, according to all the varied conditions of their origin and composition (including impurities or accidental elements), the location of their ultimate origin as clays, and the complex relations of transportation and deposition, which may alternate in sequence, and vary in detail, almost indefinitely. Especially is this last true, because of the indefinite term of life, under ordinary conditions, which belongs to the essential minerals of clay, inasmuch as they themselves are the product of the destructive chemical activities, commonly acting on rocks. The first group under the head of TRANSPORTED CLAYS is, by far, the most important; and it is termed Sedimentary, because the claybeds, classed under it, all have their immediate origin as sediments, as clay minerals, sorted out, in a large measure, by the differential, transportive power of moving water. The Marine Clays include those, deposited beyond the range of fresh water. They are subdivided into the deep-sea clays, and those bordering the shores. I The Lacustrine Group includes fresh-water lake deposits; and the Stream Group, those clays, which have been deposited, either on the borders, or at the mouth, of the streams, as parts of either flood-plains or deltas. I These clay formations, as they are now in process of development, have been exhaustively dis cussed, in the report on the Deep Sea Deposits, in the reports of the Scientific Results of the Voy age of H. M. S. "Challenger", I891. 12 DISCUSSION OF THE PROPERTIES OF CLAYS The subdivision, called Meta-sedimentary; is meant to include those, which are not transported as clays; but which are the chemical product, from the decomposition of other transported sediments, such as volcanic. tufas, pumice etc. That this process takes place, especially in the deep seas, is established by the results of the Challenger expedition. The subdivision, entitled Residual, includes those clays, which have, in their past history, been transported; locked up (in relatively small quantities) in calcareous formations, which have been elevated as land areas, and finally dissolved away, leaving, as a residuary mass, unweatherable clay particles. Our most plastic clays are of this sort, and occur in beds and pockets, in our limestone formations, and in the bottom of limestone caves. The basis of many of our soils is of this immediate origin. The subdivision, called Unassorted; includes those which are commonly called Till or Boulder Clays. They are transported by glacial ice, which has little or no sorting power, and, consequently, deposits them, without definite bedding-planes, and mixed with a heterogeneous collection of sand, pebbles and boulders. ORIGIN AND COMPOSITION Clays originate, as has already been stated, as products of the decomposition of various silicates of aluminum. These are chiefly members of the feldspar group, and, probably, are most largely orthoclase and microcline. The feldspars are essentially double !?ilicates of aluminum, and either potassium, calcium, sodium or DISCU,\~\10N OF TIIE PROPERTIES OF CJ,A YS I 3 barium, which often replace each other. \Vith these are usually small percentages of magnesium and iron, due to the presence of mineral inclusions. The exact state of combination of these elements is not known; and the nature of the change, which takes place, on decomposition, is not completely understood; but, in general, it may be said, that the feldspar molecules are broken up. A portion of the silica combines with the alumina, and these two unite with one or more molecules of water; the alkalies and other elements, present in the feldspar, pass into other combinations, usually soluble salts, according to the nature of the chemical solvent. At, or ncar, the surface of the earth's crust, it is probable, that this solvent is usually carbonic acid, in which case, the initial accessory products would be largely soluble carbonates. There are probably other methods, in nature, of decomposing the silicates of aluminum, and producing the essential minerals of clay. Some authors 1 claim, that this has been done, to a large extent, by the action of fluids, containing fluo-silicates, or fluo-borates, which act from below. Experiments ha\e been made, by Collins, 2 proving, that feldspars are converted into a hydrous silicate of aluminum, by hydrofluoric acid, and indicating, that orthoclase, of the feldspars is the most readily and completely altered, by this reagent, and labradorite, the least so. The occurrence of secondary minerals, containing fluorine, such as tourmaline, topaz, gilbertite etc., constantly associated with kaolin, the hydrous silicate of aluminum, have led the authors cited, and others, to the conclusion, that hvclrofluoric acid has been at 1 Von Buch ancl Daubt6s. 2 Cf. Min. ~lag .. \"ol. \'II. Ko. :);, p. zo;, on "The Nature and Origin of Clayo,'' by J. H. Collins. DISCUSSION OF THE PROPERTIES OF CLAYS least one of the important solvents leading to the production ot kaolin. The ultimate origin of clays is, then, involved in chemical processes, which result, in the production of the essential clay minerals, hydrous silicates of aluminum, associated with other products of chemical changes, and the residuary minerals and mineral fragments, which are undecomposed. Such a mass, if it remains in situ, is subject to further chemical changes; to the removal of all or part of the portions, soluble in surface water, and not at first removable in solution; and to the introduction of new material, by infiltrating waters. The additional chemical changes, under ordinary conditions, may consist, either in the continued destruction of the minerals, not wholly decomposed, before the mass becomes essentially clay; or, in the construction of new minerals from the elements, which are already present, or in combination with those, which may subsequently be introduced. Such clay will vary in character, according to the nature of the rock, from which it is produced; the nature and completeness of the processes; the nature of the chemical solvents; the action of surface water, either in moving or introducing new chemical elements; and, further, according as it may be subjected to the influence of heat or pressure, which tend to convert the clay into slates and other rocks. All clays have this ultimate origin. The transported clays have, however, a more immediate origin, determined by the conditions of transportation and decomposition, which have already been pointed out. These conditions may vary endlessly; and the endurance of the clay minerals enables them to survive indefinite cycles of removal and decomposition; and they pass from mountains to valleys, from continents to sea-floors, from region to region, until they are finally destroyed, by the metamorphic action of heat. pt D!SCUSSJDN OF THE PROPERTIES OF CLAYS I 5 The hydrous silicates of aluminum, which, according to the definition given above, are the essential minerals in clays, vary in composition, so far as they are modified, by varying amounts of combined water, and different ratios of silica to alumina. Much analytical work has been done, in connection with this problem, with disagreeing results, largely due, probably, to the lack of application, by investigators, of a systematic and uniform method, in making analyses, and to the want of care, by them, in ascertaining, whether the mineral analyzed contained impurities. Based on the work of various chemists; on that of investigators, using the microscope, with high powers; and on the physical experiments of Le Chatelier; 1 it may now be said to have been established, that there are various hydrous silicates of aluminum, which differ in proportions, in which the elements are combined, and in form and structure, some being colloid or amorphous, and others crystalline, in either the monoclinic or rhombohedral systems. The most important of these is kaolinite, the accepted formula for which is Al20:1, 2 Sio2, H 20, the percentages being, Silica, 46.3; Alumina, 398; and vVater, I 39 Pure clay consists, therefore, of alumina, silica and water, chemically united. The common mineral impurities are quartz, feldspar, m1ca, chlorite, pyrite, hematite, limonite, calcite, gypsum, alum, rutile, dolomite, opal, or hydrous silica, and organic matter. These minerals furnish, chemically, in the main, silica (hydrous and anhydrous), potash, soda, lime, magnesia, iron, in various forms, sulphur and titanium. These elements and compounds modify the properties 1 Lc Chatclier clas~itics the hydrous s1lic1tes ot aluminum, according to the amount of water. chemically combined in them, which he ascertains, by determination of \ariations in the rate of increase of temperature, broug-ht about by the clay yielding up its combined water, and detected, by means of his thermopyle pyroructer (which has been described in a number of scientific journals), so applied, as to record, photographically. along the scale, the rate of increase of temperature. See Bull. de Ia Societe de 1\Jincralogie, Nos. Sand 6, rS87, De l":Hcion de la Chaleur sur les .~rgiles. 16 DISCUSSION OF THE PROPERTIES OF CLAYS of clays, in v"arious ways, both as physical units and by chemical reactions. The size of the particles, composing the average clay, range from that of coarse sand, relatively small in quantity, and often wholly absent, down to the minutest microscopic particles. Beyond these, are an abundance of fine particles, which will render water opalescent, remaining suspended in it for an indefinite. time. As regards the composition, or mineral identity of the materials, which so remai.n indefinitely suspended in water, no chemical determinations have been made, so far as is known to the writer. Prof. Whitney includes all these ultra small particles, in what he terms his "clay group." An objection may be raised to this use of the word "clay", which is a term used for rock, consisting essentially of kaolinite. In the case of these minute particles, it has been shown, that they are, in greater part, fragments of this mineral. Theoretical considerations would indicate, that they are likely to be quartz, in as great, if not greater, measure than kaolinite; and, hence, the material might be considered sand, often, with more propriety than clay. The term clay should not be used on the grounds of fineness of material, alone, if this is the case. The actual nature of these particles being undetermined, their character may be inferred, as follows:- The great mass of fine grained, fragmental rocks will consist of those minerals, which are both extremely abundant and most highly resistant to the destructional forces, known as "weathering". In these respects, quartz and kaolinite vastly exceed all other minerals. The rate of abrasion of rock fragments diminishes rapidly, as they decrease in size. A point will, therefore, be reached, where the abrasion of particles suspended in, or transported by water, THECLA V$ Oft' GEORGIA C HARACTERISTI C VIEW IN A RAILWAY CUT THROUGH WHITE CLAY BEDS, NEAR G RJ SWOLDV ILLE, JONES COUNTV, GEORGIA. will practically cease. Such particles would naturally be in a well rounded condition. The great mass of particles, smaller than these, will originate 1n the minute condition, broken from the peripheries of larger bodies. It has been shown by experiment, that minerals, ordinarily insoluble in distilled water, will be found dissolved therein, after abrasion, showing, that blo\\s between masses, large enough for effect, wi 1I possibly reach, in tearing substance away, clown to the molecule of matter. From the fact, that the extent of surface increases relati,ely, as the mass diminishes, small particles are more readily attacked and destroyed by chemical action. So, that the sifting process, tending to preserve quartz and the kaolinite, as residuary materials, is heightened in productiveness. As to the relative amounts of quartz and kaolinite, among the extremely fine particles, the preference would seem to belong to quartz, unless it can be shown that kaolinite crystals occur with exceedingly small diameters. Minute products of abrasion will be most abundant, of the material, fragments of which occur in masses. large enough to give and receive, under the conditions of water erosion, effective blows. \Vhile this is universally true of quartz, it is only so of kaolinite, to a most limited extent; because the crystals of this mineral, being themselves small, are thus less likely to suffer from abrasion, than is quartz. Despite this fact, however, the presence of a perfect cleavage in the kaolinite needles permits them to suffer most extensive subdivision; but, with this difference from quartz, that, while the latter can furnish an unlimited number of particles, of varying size and shape, the kaolinite particles will rarely be smaller, by natural abrasion, than the cleavage scales, which separate from 18 DISCUSS'ION OF THE PROPERTIES OF CLAYS each other. Owing to the small size of these, they escape further destruction, and preserve, in the main, two of their dimensions intact. This seems generally true; for a microscopic study of clays reveals the essential mineral present, commonly, as small, thin scales, averaging about .003 of a millimeter in diameter, with most of their crystal angles still preserved. Original size of the fragments and molecular structure, then, seem to limit the smallness of kaolinite particles, and to determine their shape, while they lead to the production of quartz grains of any degree of fineness, and of any shape. PROPERTIES AND CHARACTERISTICS The properties and characteristics of clays depend upon, first, the kaolin minerals, and, second, the impurities. In the case of the former, the condition, in which their fragments are found is important; that is, whether their individual particles consist of prismatic crystals, minute plates or thin cleavage scales, resulting from either the simplest form of disintegration of the original crystal, such as is brought about by the action of frost, or from abrasion, suffered, during transportation from its place of origin to its home, as a sedimentary deposit. In the case of the impurities, much depends upon both the absolute and the relative quantities of each, present, and its state of fineness or subdivision. Clays are characterized by no special Color. The pure variety is white; but they commonly occur gray, drab and bluish, often mottled and variegated. They are, also, found of almost all colors, frequently being brilliantly tinted with reds, yellows and purples. p: IJ/SCUS'S/0,\- OF Tille' I'ROI'F!t' TIFS OF Cf./1~~ On~anic stains give a variety of colors, often brilliant in hue, purple and red being the most striking. Different compounds of iron, the most common coloring causes, give greenish, gray, yellow, br0\n1 and red tints. The colors are deepest, when the clay is moist, and they grow lighter, as it is dried. These color~ affect the usc of the clay in its ra\v state; as tor example, its use in the manufacture of wall-papers, the adulteration of foods etc. In most cases, its color, in the natural state, enables us to infer the color of the burned product. Organic stains, however, c!isapl'car on burning, while the iron stains are modified or developed, b: both the intensity of the heat employed, and the degree of oxidation effected in the process of burning. Clays are usual! y characterized by a peculiar Odor, or "argillaceous smell", which is not invariable, and by a smooth, unctuous hd, which is also frequently absent, being dependent upon the fineness of grain, and the absence of coarse impurities or grit. In Dmsit)'. llardncss, Tmacit)' etc., clays differ wide! y, being moditied. in these particulars, by their geological history. Among the crystalline rocks, where they originate, they are apt to be coarse and loosely coherent; but often transportation and secondary changes, \\ hich they may have undergone, following their accumulation as sediments, such as compression, the loss of water, infiltration of mineral matter etc., changes their general structure widely. They vary from soft, porous, incoherent masses, through tough, compact varieties, \Yhich arc often laminated or ha\c a fissile structure, on to exceedingly tough, and even to varieties, which are so hard, that splinters, flying from beneath the blo\\' of a heavy hammer, will cut the flesh of a \Yorkman. Such clays belong to the class, kno\Yn, commonly, a:; "flint clays"; and they are mined only by drilling and blasting. 20 DISCUSSION OF THE PROPERTIES OF CLAYS The degree of hardness varies, in the scale of I o, used by mineralogists, from I to 3 5; but this is hardness of the clay mass, technically a rock, and not that of the individual clay or kaolinite particles, the hardness of which has not been accurately determined, owing to their extreme smallness. The specific gravities range, from less than I to about 2. 5, pure kaolinite having a specific gravity of 2.60. The specific gravity, of course, varies with the state of compactness of the mass. One of the Georgia clays will float, for a time, in water; and, when coated with a thin film of paraffin, it floats like a cork. BEHAVIOR OF CLAYS, WITH REFERENCE TO WATER AND TO HEAT The most important properties of clays are those, developed by their behavior, with reference to water and to heat. Water Absorption, Plasticity, Sltrinkage and Consolidation on Dryi11g are the important phenomena, resulting from the relations of clay to water. The molecules, of which clay and water are composed, have a strong mutual attraction. As a result of this, a single dry kaolinite scale, exposed even to ordinary atmosphere, will rapidly absorb moisture, condensing it, as a film on its surface. This attraction is so strong, that experimental results, by the writer, have shown, that dried clay will absorb moisture, thus gaining in weight, even when enclosed in a chloride-of-lime desiccator. pt 2 D/SCC:SS/0~\' OF TilE 1'/WI'ERT/FS OF CLJ JS 2I :\n aggregation of kaolinite scales, constituting a mass of clay, may be looked upon as a labyrinth of capillary tubes. Owing to the tension, or pull, on the free surface of liquids, which is described by physicists as "surface tension", water will move in small tubes, indepenclentl.\' of graYity, falling below its normal position, when there is no attraction between the water and the walls of the tube, to counterbalance this surface tension; as, for instance, if the ,,alls \Ycre coated ,,ith a film of grease; and it will rise, above its normal height, acting against gravity, when there is an attraction between the \Yater and the substance of the given tubes. These arc known as capillary phenomena; and, in the case of clay, with its capillary labyrinths, water \Yill rapidly penetrate the mass, until the supply fails, or, until the weight of water in the tubes exceeds the other operative forces. It is in this manner, that clays absorb moisture, doing so, very rapidly, when the particles are loosely aggregated; and more slowly, though still effectually, when they have been compressed into ever so compact a mass. On exposing to water, dry clay powder, which has not been compacted by pressure, the former replaces the air in the interstices of the clay; and, owing to the strong attraction between the water and the clay, it draws the particles more closely together, and thus accomplishes a Primary Slzrinkagc of the mass. Clays, which have not been indurated, by the infiltration of silica, or other soluble mineral matter, or by some form of recrystallization, no matter how dense or hard they may be, will dissolve, when exposed to water, even though the whole mass be not in contact with it. This phenomenon is called "slacking", and is clue to the penetration of the water between the minute kaolinite scales, in the manner described above. If, then, an incoherent, dry clay powder be given an opportunity, 22 DJSCU~'SJON OF THE f'ROPFRT!ES OF CLI YS it will absorb a definite amount of water, dependent upon the fineness of grain and shape of the particles, and the compactness of the mass, and will shrink, in the ratios, also, of these same conditions. SHRINKAGE AND CONSOI,IDATION ON DRYIXG If, in a moistened or wet condition, clay be subjected to heat, but slightly above the boiling point, the moisture will be expelled, or, more properly, will be absorbed by the atmosphere. It departs, under these conditions, molecule by molecule, film after film, being removed from the exposed surfaces, which are those in the open ends of the minute tubes or fissures in the clay. But, as soon as a film of water is removed from one of these tubes, the weight of the column is diminished, and, by "capillary attraction", there is a tendency to elevate the water to its original height. This can only be accomplished, assuming a new supply of water from any source to be prevented, by a possible shrinkage of the whole; or by its breaking into parts, which shrink upon themselves. The completion of this process may be termed, for convenience, the Secondary S!trinkage of clay. It results in a more or less consolidated substance, the degree of consolidation depending upon the nature of the clay particles; and, essentially, upon their small size and peculiar shape; that is, that they are minute, thin scales. These remarkable characteristics, which are phenomena, so common and so apparently simple, that they seem never to have received more than superficial explanation, are produced by forces, brought into play by two physical processes, -nothing more than adding to, and removing water from, clay powder; and, but for the p part played by these forces, the material would again be an incoherent powder, at the close of the processes. This aspect of the case seems to have been, hitherto, overlooked by clay imestigators, who have explained shrinkage, by the mere statement, that it is due to the loss of interstitial \Yater; but, if this alone took place. unaccompanied by the action of other forces, the \\et clay, on drying, would, of course, fall again into its original state. The effect is, that, as the water is removed by evaporation, "surface tension", on the free surfaces of the \\ater, co-operates \\ith the attraction bet\\een the molecules of water and kaolinite, and a pull is inaugurated, which shrinks on the one hand, and consolidates on the other; the latter, by bringing the clay particles within the realm of mutual attraction, or to the point, where friction, or the interlocking of surfaces, of the particles gives strength to the mass. The amount of shrinkage, and the degree of consolidation, for clays of a given density, are largely dependent upon the fineness of grain and the shape of the particles, and the condition of the surfaces and edges of these; that is, whether they are relati\'cl\' smooth or rough. The coarse clays, or those with much impurity, shrink but little, and show but little tensile strength. Clays, mixed with enough water, to make them only plastic, shrink in amounts, ranging from about I to I o per cent. \Vhen dried, from a condition of self-saturation with water, they shrink in amounts, ranging from 5 to, at least, 30 per cent., linear measurement. The degree of consolidation, measured in tensile strength, varies enormously, the variation being from a few pounds, in the case of "flint" clays, to between three and four hundred pounds, in the most plastic clays, per square inch. The manner, in which shrink- 24 DISCUSSION OF THE PROPERTIES OF CLAYS age and consolidation on drying are brought about,.may be explained by reference to the following diagram, fig. I. Fig. I Diagram to Illustrate Shrinkage and Consolidation. This figure illustrates, diagrammatically, the beginning of evaporation of water from a mass of clay, which has been allowed to absorb the former, to the point of saturation, through perforations in the bottom of the containing vessel, the latter having now been removed from the water-supply. So long as water could be drawn up from below, while evaporation was going on above, there would be no change in the conditions, except the gradual movement of water upwards; and no necessary movement of the clay particles in any direction. When the supply of water is removed, surface tension at (a) still operates to elevate water to the original height. If there were no points of weakness in the mass, that is, if the conditions were uniform throughout, and each particle were fixed in its place, there would result, of course, only a gradual subsidence of the water. If the particles, however, be considered free to move in any direction, uniform as regards their size, shape and distribution, and if the affinity of water for the sides of the vessel be exactly equal to that for the clay, a vertical shrinkage will take place. The capillary attraction, capable, originally, of lifting water to the points (a), would still be operative; and water, to replace that D!SCC~SJ(Ji\~ OF THE f'ROI'ERT!ES OF CL/1~.<.; .evaporated, would be fed from those channels, the walls of which arc the most easily collapsible; and, with the given conditions, these would be the lateral ones, the downward movement being facilitated by gravity and the presence of the one free surface above. It must be borne in mind, that the tension, at the points (a), and beneath them, throughout the process, is of uniform value in each and every tube. If, as in the case of our experiment, the affinity of the clay for the water exceeds that of the walls of the vessel, a point will be reached, where the up-pulling at (a), between the clay particles, will remove the water from the columns adjacent to the sides. The mass is then free to shrink upon itself, in horizontal directions, as well as vertical. \Vater is fed to the exposed surfaces, so long as the particles can approach each other. Shrinkage has been accomplished. and consolidation results, from the bringing of the fine particles. within the realm of mutual attraction, and from intersurface friction. \Vhen this takes place in nature, the lateral tension is unable to contract the mass as a whole. Owing, however, to inequality of conditions, planes of separation are established along lines of weakness, and so-called "mud-cracks" result. The smaller masses, thus formed, may then shrink farther. In the arts, this phenomenon is called Clucking. The finer grained the material, the greater the amount of surface -of the particles, as compared with their mass. Consequently, there are more contacts; mutual attraction and friction is more effective; and the mass more completely consolidated. In the case of sand, the mass of the individuals so far exceeds the amount of surface, at which contacts exist, that the bonds are ineffectual, and the material remains incoherent. 26 DZSCU.S'.SZON OF THE PROPERTIES OF CLAYS The phenomena of shrinking and consolidating, on drying, are all-impo,rtant points in the economic use of clays, in a great variety of ways. They make possible the sun-dried brick, and most, if not all, of the wares produced from clay, by burning. In a larger way, these properties of clay effect great results in nature, and some of the facts, in this connection, are worthy of special discussion, from the bearing they have on agricultural problems; and, for thi'l reason, the subject is further amplified. The behavior of. clays, with reference to water, is of fundamental importance to vegetation. These properties, in conjunction with "surface tension," operate to retain water at the surface, where it is available to furnish the moisture needed by plant life; and, also, to draw up from the "water-table" below, supplies, to renew that, removed by evaporation and the requirements of vegetation. It carries, held in solution with the water, the mineral foods, which build the tissue, and support the growing plants. It also forms a crust produced through shrinkage, which retards evaporation. Prof. Whitney, in the introduction to "Some Physical Properties of Soils," states, that chemical analysis has not explained the relation of soils to plants, or the local distribution of the latter; that the general distribution of these is determined by temperature and rainfall, but the local distribution, by the relation of the soils to moisture. Prof. Whitney (whose works on Soils and Crop Distribution,' should be read by every person, interested in scientific farming), in discussing the circulation of water in soils, shows, that it is affected by the presence of salts and organic matter, in solution, and describes the practical results of this, on water and food supplied to 1 "Some Physical Properties of Soils in Their Relation to Moisture and Crop Distribution";. U.S. Dept. of Agri., Bul. No. 4,.1892. "Conditions in Soils. of the Arid Regions;" U.S. Dept. Agri. Yearbook, 1894. "Reasons for Cultivating the Soil"; Yearbook, U.S. Dept. Agri., x8g5. !J/S( '{ SS/0.\' OF !'/IF I'NOI'EN'J'f!:.\' OF CLI J .\ plants. as modified by the use of fertilizers. Great stress is laid by this author, on the relcttion of plants to the texture of the soil, ,rhich, of course, affects capillary circulation. If the statements, \\hich have been made, above, are true, can it not be reasonably claimed, that, without the properties of clay under consideration, together with the surface tension of water, the very existence of land vegetation, or at least the greater part of it, would be threatened~ But for capillarity, would not rain waters escape through or over the soib too rapidly, to be available': \Vould the film of water, directly attracted by each grain of soil, succeed in resisting evaporation ( and, if it did, how extensively would it support vegetation ~ \Vhere would plant food come from ( Another, more fundamental question:--- To what extent would the fine-grained materials, constituting soils, accumulate: In short, would land \egetation have a soil, permanent enough to grow in i From a consideration of the facts, it is evident, that the existence of the former and the permanency of the latter are largely interdependent, and that, besides this, each is directly dependent (the degree being the only question) on the conditions, as stated above. If, as has been shown, clays and soils should dry without their influence, they would dry into incoherent "powder", "sand" or "dust"; and no crust, more or less solid, would be formed. On the other hand, if they did not operate to elevate, in soils, water from below, they would dry, after wetting, in a much shorter time. In the former case, soils would be subject to erosion, to a vastly greater extent, than they are, owing to the absence of a crust, and the general consolidation, shown to result from drying. In the latter case, the presence of the water, obtained by capillarity, renders the soils somewhat tough and coherent, in a different fashion; and so, again, it tends to retard erosive agencies. 28 DISCUSSION OF THE PROPERTIES OF CLAY.'> Thus, in two direct ways, these materials are preserved from ero- sion by the wind, the impact of rain, and flowing water. Indirectly, a growth of vegetation is made possible, which further, and so largely, protects the soil from erosion. Moreover, this veg- -etation is a source of chemical decomposing agents, which accel- erate soil accumulation. The following generalizations are grouped together, here, as an outline of the featut'es of the circulation of water in soils:- 1 rst. The soils are composed of mineral matter of different sorts, chiefly -quartz, feldspar and clay (kaolin); and these occur in sizes, ranging from that of the particles in coarse gravel down to minute rock fragments, .ooor of a millimeter in diameter. 2 They are, also, of different shapes, the quartz grains varying in form, from angular to well rounded, while the clay or kaolin constituents are commonly present as thin, flat scales. znd. The state of aggregation of these, and the relative amounts of each, present in different soils, varies enormously. 3rd, The affinity of the soil particles for water varies with their chemi-cal nature; and particles of the same material have a varying affinity, un.der different conditions, not, now, well understood. 4th. Salts and organic matter, in solution, modify the value of the surface tension of the liquid, the former generally-increasing, the latter de-cr~asing it. sth. The circulation of water is of two sorts, viz., (a) flow due to hydrostatic pressure, or gravity, and (b) flow due to capillarity. 6th. The permeability of the soil to water, moving under the influence of gravity, depends largely on the size of the tubes. The smaller the tubes, the slower the rate of flow. 7th. The penetration of the soil by water, acting under the influence of capillarity, depends largely, also, but in a reverse way, upon the size of the tube. The smaller the tubes for a given total area of cross-section, -the greater the amount of water absorbed, and the higher it is elevated. 8th. For a given soil, the retention of moisture, when loss, from evap- 1 For general discussion, see Whitney, op. cit. 2 In this connection, Whitney states the interesting facts, that, on the average, about so per cent. -of the volume of soils is space, occupied by only air and water; that, in a cubic foot of soil, the grains have, on an average, at least so,ooo square feet of surface; and that soils, containing from ro .to 30 per cent. of clay, consist. respectively, of from four to twelve billion grains. DISCC\SJON OF THE I'ROPEII'TJES OF CL"i VS oration, is suffered, depends upon the size of the capillary tubes; the affinity of the soil particles for water; the amount of water-supply; and the length of the capillary tubes, or the distance of the "water-table" below the surface. 9th. Its retention of moisture, when suffering loss through escape below, depends, in a great measure, upon the size of the capillary tubes, the rate of flow, through these, for a given amount of pressure, varying, as the fourth power of the diameters. 1oth. Soils, subsoils, and the water reservoir, may all differ in texture. The rate of flow of water to the surface, depends largely upon the nature of the texture of these, and the relative positions, which they occupy. Further, the penetration of the ground, by meteoric waters depends largely upon these same conditions. IIth. Both the presence and circulation of wate!" in soils depend upon very complex conditions, such as, the nature, size and shape of particles,. their state of aggregation, or the texture of the mass, and the position and amount of water-supply. PLASTICITY Plasticity may be defined, as the capability of a substance for being moulded by a readjustment of its physical units, with reference to the moulding force. Strictly speaking, it is not a property of clay, though it is usually spoken of, as being, perhaps, its most important one. Perfectly dried clay is not plastic. A mixture of clay and water, in certain ratios, which vary within fixed limits, may be extremely plastic. Such a mass may be 'moulded at will, and readily retains the final shape, to which it is brought. This behavior is of the greatest use, of course, in manufacturing clay-products, so many of which are moulded, then dried (when they consolidate, as shown above), and finally burned. The cause of plasticity in clays has been a subject of conjecture and discussion, for many years, Cook being one of the earliest American investi- 30 DISCUSS/ON OF THE PROJ'ERTJES OF CL1l'S gators, to call attention to the question. He rightly inferred the relation existing between this property and the shape and size of the indiYidual particles. A number of observers have assigned plasticity, more or less remotely, to the chemical composition of the clays,- that they are aluminous and hydrous; and this theory, or rather conjecture, is, in a measure, correct. The chemical composition certainly participates in the cause, though, just how it is connected with the phenomenon, the advocates of the theory have not satisfactorily shown. The fact, that some clays, more impure than others, are the most plastic, has long been known. It has been suggested, that the presence of vermicular-formed crystals, and irregularly angular particles may have a bearing on the question of plasticity. Facts, however, show otherwise; and the suggestion does not deserve to be dignified with the title of "Theory of Plasticity." It has, also, been shown, by experiment, and has been long recognized, that fineness of grain, and, as Johnson and Blake have brought out, r the shape of clay particles are, also, factors; their researches show, that, when these plates occur in aggregates, instead of individuals, the clay is decidedly less plastic. Prof. Haworth has lately made researches along the same line, and has arrived at the same conclusion. The true explanation of plasticity can best be arrived at, by looking at the conditions involved. For the purpose of these considerations, clays may be conveniently divided into three classes:First, Those, which occur in their place of origin,- that is, the indigenous clays, which consist of plates, variously aggregated, and prismatic crystals; second, those, which have been transported, broken up into cleavage scales, and deposited in degrees of fine- 1 On Kaolinite and Pholcrite, Am. Jour. Science, II, \'ol. XLIII. pp. 35 and 36. r867; Johnson and Blake. DISCCS.SIOY OF THE PROPERTIES OF CL4 VS 31 ness. according to the sorting power of water, moving with different rates of flow; and t!tird, those, which have been indurated, either by cementation, recrystallization or some unknown cause, to the point. where they will no longer slack, in water. In order to make the clays of the last class plastic, they must needs be first ground. The other t\\'O classes are both plastic, the former the least so; while, of the latter, those, which arc the finest in grain, having been carried the farthest, or deposited in the quietest \Yater, are the most plastic of all. These clays differ, respectively, in a marked degree in plasticity, according to the amount of interstitial water, which they contain. A certain percentage of the latter. differing in the different clays, gives a maximum plasticity. These facts evidently tend to show, that Fineness of Grain is one of the necessary factors; but a comparison of clays with other finegrained substances shows, that fineness of grain alone is insufficient to account for the facts observed in the behavior of clays. As already mentioned, the microscopic examinations of Johnson and Blake have shown, conclusively, that Sltape of the particles is also a determining factor, and theoretical considerations, to be discussed later, accord with this assertion. Another factor, which is of supreme importance, is the Mutual "Jttractiou, already referred to, which exists between water and clay particles, under normal conditions; and it is here, obviously, that the chemical composition of kaolinite has its bearing, though, not in the manner, which has ever been assigned to it, as a cause. Of equal significance, and of necessity as a factor, is the Suiface TmSUJil, ' acting on the free surfaces of the water in the clay mass. 1 The term, "surface tension", is the familiar one, used by physicists to denote certain molecular conditions on the superficial film of bodies. Owing to the absence of cohesive attraction on the ont~ide ot such films, there exists a relatively greater stability of position among its molecules, with reference to movement outwardly from the mass. and a tendency to diminish the extent of surfaces, or a "('o~f(zce full,- a resultant of molecular forces acting alone from within. 32 DISCUSSION OF THE PROPERTIES OF CLAYS Compared with these factors, the questions of fineness of grain, shape of the particles etc. are insignificant; at least, they are very much less fundamental. To sum up the situation, we have, in any given suitable sample for demonstration, a mixture of innumerable, minute, thin, flat particles, separated from each other by films of water, the two attracting and holding to each other, with a force, often greater, than that, by which the water attracts itself. The water, which is a fluid, acts as a lubricant, and facilitates the moulding of the mass. For this purpose, enough water must be present, to perfect this property. Having been moulded, the mass has rigidity enough to maintain its shape, when too much water is not present. The difficulty, that seems to need explanation, is, that a heavy mass of particles, mixed with such a liquid substance, can retain almost any shape given to it. The explanation is, that a relative rigidity is given to the water itself by the pull, existing between it and the clay particles, over a vast extent of surface, permeating the whole, and co-operating with surface tension, which participates in holding the water, as does, also, friction, throughout the mass. The questions of fineness of grain and shape of the particles become, then, largely, but modifying factors, affecting degree, and being, within large limits at least, modifiers, rather than determinants of plasticity. For instance, coarse, angular quartz sand, when moistened, becomes plastic, to a considerable extent. It does not, however, on drying, consolidate; but the consolidation of a substance, on drying, and plasticity are, as thus shown, quite different matters, and should not be confused, as they seem to have been; because they are, to some extent, dependent upon similar conditions, and are associated phenomena. THE CLAYS OF GEORG!A PLATE !II WHLTE CLAY AND SANDS OVERLALD BY TERTIARY ROC KS, RICH HILL, NEAR KN OXVLLL~:, G IW RG IA. D!SC[:SSfO~V OF TJIE PROf'JUOiES OF CLAYS 33 The diminutive size of the particles acts as a factor, in two ways_ In the first place, the smaller the particle, other things being equal,. the more readily a number of them will move over each other. In: the second place, the smaller the particle, the greater the amount of its surface, as compared with its mass. Prof. \Vhitney, in the papers quoted, frc. I .. ' ~ DISCUSS/Oil! OF THl'; PROPERTIES OF CIA YS 35 .stance fuses, and complete readjustment of the molecules takes place; and the product, as it is ordinarily cooled, is a kind of glass. These processes, the loss of combined water, and different degrees of vitrifying, produce a third, or tertiary, shrinkage of the mass, known as fire-shrinkage. If the clay is free from impurities, .an enormous temperature is required, to bring about complete fusion; but, in an electric arc, where the voltage is high, it fuses .into liquid glass, more quickly, than wax melts in the flame of a candle. It will also fuse, but less readily, in the oxyhydrogen furnace. Clay, which IS comparatively pure, and fuses only at relatively high temperature, is called Refractory or Fire Clay. The processes, by which incipient and higher grades of vitrification are brought about, in the arts, are termed burning or jiri7lg, and .are conducted in kilns or furnaces of various sorts. Impurities of different kinds modify, in different degrees, respectively, the refractoriness of the clay. Two substances, which are, by themselves, highly refractory, will, when in intimate contact, unite chemically to form new compounds, and thus fuse, under these conditions, at comparatively low temperatures. This is the important principle, by which the effect of impurities, in lowering the fusing point in clays, is accomplished. Besides modifying the fusibility of the clay, the impurities affect the color of the burned product, as spoken of, in discussing the color of clays. The common coloring agent, in burning, is iron, which gives a variety of shades, ranging from buff artd salmon, to red, brown and black. The relative effect, of the different impurities on the fusibility .of clay, will be spoken of, under another heading. USES OF CLAY USES OF CLAy I Clay is used, in the raw state, chiefly, as sun-dried bricks; for the adulteration of various food and other products; and in the manufacture of paper, principally wall-paper. For the two latter purposes, fineness of grain, color, and freedom from grit are the essentials. The wall-paper industry is the most important use, to which clay, in its native state, is put; and it is this demand, which the Middle Georgia clays should seek to supply. Such clay brings from $8.oo to Sro.oo per ton, of 2,000 pounds, delivered in New York; or, on the average, about $5 .oo per ton, at the mines. It is used, to add weight to the paper, and to enable it to take clearer impressions, in printing. Originally, a variety of talc and whiting were used; but, at present, the manufacturers use almost wholly the fine-grained, pure-white clays, which slack easily in water, and which are found mostly in New Jersey, Delaware, Maryland, South Carolina, Georgia and Florida. Fifteen to twenty per cent. of clay is added to each r ,ooo pounds of pulp, though the latter usually retains not more than half of this, in its final state. Not less than ro,ooo tons, and probably much more, of this clay is annually consumed, by the wall-paper trade alone.2 The use of clay, in the raw state, constitutes but an insignificant part, in the total consumption of this material, in the world. Its chief use is in the manufacturing of burned products, of many I See list of publications in appendix. 2 A brief account of the use of these wall-paper clays will be found in the ,tfanufadurers Record, of Aug. I3th, I8<)7, p. 33, in an article, entitled" Southern Paper Clays," by H. K. Landis. CSES OF CLdY 37 sorts; and for this purpose, there is manufactured, at the present time, in the United States, alone, a product, valued, probably, at not less than S;o,ooo,ooo, annually. The statistics, compiled by the United States Geological Survey, show a valuation of our clayproducts for r8go, of $6;,77o,6gs, and for r8g4, of $65,389,784. These figures are, in all probability, too low; as a large number of the minor industries are, unavoidably, omitted, in the reports, which are made to this department. The burned products may, in a rough way, be classified into household wares, including porcelain and china wares, and art pottery of many kinds; structural materials, including buildings, bridges, culverts, road-beds etc.; drainage materials, such as sewerpipes and drain-tiles; and refractory materials, that is, products, which will withstand high temperature, and, in cases, the corrosive action of chemical agents. These latter are main!y structural, such as fire-proofing, now used extensively in large city buildings and factories; linings to retorts and furnaces; and utensils, in which glass is melted, fusions made for assays, etc. Following is a list, including, in a general way, most of the products made of burned clay:- Common brick; ornamental, pressed or front brick; paving-brick; enameled brick; washed brick; fire-brick; roofing-tile; encaustic, panel and floor tile; terra-cotta; terra-cotta-lumber; drain-tile; sewer-pipe; glass-pots; gas retorts; crucibles; porcelain, common and art pottery; plumbing articles; and electric insulators. For the methods of manufacturing these products, the manner of preparing the clay, etc., the reader should seek the general literature on the subject, a number of references to which are given, at the end of this report. DISTRIBUTION OF CLAYS GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION Clays are common to all countries, having the diverse distribution of fragmental rocks, as well as that of the feldspathic igneous rocks, from which they are being constantly formed. In the geological scale, clays occur among rocks of all ages; but the indigenous clays are, of course, more recent, than the rocks, among which they occur; and they may have been formed, at any time, subsequent to the solidification and exposure of the latter,. from which they are derived. The transported clays occur in all the geological formations, from the Paleozoic age, down to those of the present time; but, so far as they have been preserved in the older formations, they are more apt, to have become indurated by compression, or by the infiltration of mineral cements, or, doubtfully, by recrystallization; and many, of what were once clay-beds, in these formations, have been metamorphosed to slates, by the action of heat and pressure. In the more recent formations, they are less consolidated and more abundant. They are more abundant, here, because, up to a certain limit, the forces, which produce them, are more largely active, than the forces, which destroy them. Further, they are easily and quickly removed, by erosive action, from the older to the newer formations; and they lose nothing, destructively, in essential character, through the process of transportation. CHAPTER II METHODS OF SEEKING AND TESTING CLAYS Clays are located, chiefly by observation in the field; in cuts along highways and railroads; on stream banks; and in gullies, in the fields and forests. They arc found, also, in sinking wells, and by boring, and they may be systematically sought by trained geologists, who infer probable location and position, from a variety of observed geological facts. \Vhcn found, the expert can arrive at an approximate estimate of their possible utility, by a brief examination, known as macroscopic investigation, this meaning, merely, the hand study of a specimen. The color is observed; the taste and feel are noted; its structure and relative freedom from sandy impurities arc determined (by means of a pocket lens, if necessary); and its slacking quality and plasticity arc tested, by wetting with water. Such an expert will, also, note its manner of occurrence; probable thickness and extent; nearness to market, and to means of transportation; the amount of stripping or over-burden, etc. SAMPLING As a preliminary to laboratory tests, the clay occurrence should be carefully sampled; as it is useless, to undertake the expensive (39) 40 FROSFECTINC AND TESTING investigation of a clay, unless it is known, that enough of such material is available to warrant its development. Samples should, therefore, be so collected, as to represent, if not the average of the occurrence, at least a part of it, which can be profitably separated from the rest. This question of sampling is one, of the greatest importance, and it should only be undertaken, by some one, thoroughly familiar with clays and their uses, clay-bodies being very rare indeed, which are uniform in character, for any considerable distance, vertically or ateally. LABORATORY INVESTIGATIONS For more detailed and more perfect determination of the value of clays, a variety of means may be adopted, for testing the nature of the properties of samples. PREPARATION FOR TESTING Since much of the value of laboratory tests depends upon the comparative use of the results, a uniform method should be employed, in preparing the clays for these. It is, of course, necessary to vary the preparation, at times, for special purposes. In general, clays, which slack, need not be ground; but, that these may be compared with flint-clays, it is sometimes advisable to grind them to a state of maximum fineness, that is, so that all the largest particles shall pass through a sieve of given mesh, which may range from 20 to I oo, to the inch, according to the test to be made. As it is necessary to do this, usually, in an iron grinder, it is advisable to pass the clay slowly over an electro-mag- l'ROSPECTJKG AND TESTJKG 41 net; or, where this is not available, to remove the tron particles, introduced by grinding, by a thorough use of an ordinary magnet. In order to determine the possible use of some clays, it is necessary to wash them, thereby removing the coarser impurities; and, for some purposes, it is advisable to separate the clay into different parts, according to degrees of fineness. This may be done, by dissolving, physically, the sample in water, in some convenient vessel, agitating, and allowing the coarser particles to subside, and pouring the liquid, containing the finer, into another vessel, a process, which may be repeated indefinitely, ever subdividing the material, according to its fineness. The following is a brief outline, ll1 a general way, of the usual preparation of clays for laboratory examination, conducted by the writer:- The sample, which should weigh not less than thirty pounds, is first divided into two nearly equal parts; and, from these, a sufficient supply of specimens is set aside, for the description of the clay, as it occurs in the field; for the purpose of microscopic study; and for the determination of its specific gravity. The first division of the clay is then ground, until it entirely passes through the sieve, of definite mesh. The remaining part is then set aside, as a reserve. From the ground and sifted clay, a part is taken, and dried to constant weight, at I00 C., for plasticity and shrinkage tests. Another part is taken, freed from iron with an electro-magnet, and set aside for the fusibility tests, and to furnish material for chemical analysis. The laboratory study of the samples then begins, and is made, with reference to their chemical and physical composition; their useful or scientifically interesting properties; and the conditions, on which these properties depend. " 42 PROSPECTING AND TESTING SPECIAL METHOD FOR SEPARATION OF CLAYS In order to separate into classes, according to the shape and size of the particles, those clays, which can be physically disintegrated, Fig. z ..... . J~ .. 0. ~ a b Apparatus for the Physical Separation of Clays. by very gentle trituration, or which will slack, use is made of an apparatus, illustrated by figure 2. This apparatus was made, as an experiment only 1 ; but it has been found useful. The idea was 1 If the original plan is carried out, an apparatus will be constructed similar to this, but differing in proportions, having a much higher tube, and a longer box, containing a long train of cars, which it is proposed to move, at a regular known rate, by clock-work. PROSPECTiNG A,\'D TESTJKG 4J suggested to the writer, by Prof. N. S. Shaler, the plan being, in case of the successful working of this experimental apparatus, to. construct one, with such modifications, as would enable it to separate particles, of various shapes and sizes, in clays and soils, and to record, in a measure, the rate of subsidence of such particles, in different solutions. The apparatus, constructed, consists of a wooden, water-tight, rectangular box, about four and one-half feet long, and six inches in height and width, inside measurement. Inserted in the top of this box, is a glass tube, four feet high and two and one-half inches in diameter I. Immediately beneath the lower end of this tube, is a double rail track 2 , on which runs a train of zin.c cars, connected with the sliding rod shown in a of the figure. The bottom of the cars are perforated, and lined, when ready for use, with filter-paper. The front of the box, where the cars are inserted and removed, is made water-tight, by means of a sheet of soft rubber, which is compressed between the box and the end, by six thumb-screw clamps, omitted in the figure. A stop-cock, at a lower level than the cars, drains the water quietly from the box. The sliding-rod moves through a brass cylinder, made water-tight by packing. In preparing the apparatus for use, the train of cars IS inserted, and connected with the piston rod; and the front end 1s clamped firmly to the box. The apparatus is then filled with water, carefully run in, through a rubber tube, inserted down through the glass. one, so as not to wash out the filter papers, which lie in the cars. \Vhen all the compressed air in the box has escaped through the pores of the wood, and the level of the water has become stationary, at the top of the tube, the piston-rod is pushed gently in, until the front car is immediately beneath the bottom of the tube. The: I See fig. 2, a. 2 Sec fig. 2, band c. 44 FR0::,7'ECTJ}\'G AND TEST/XC piston-rod JS marked, so that each car may be brought, successively, into a similar position. The clay or material, to be separated, 1s rapidly sifted through a coarse sieve 1 upon the surface of the water, at the top of the tube, at which point it is constantly stirred, by means of a \Yire rod, having a circular motion, and so used as to prevent, as far as possible, the establishment of vertical currents; or the clay is introduced, already in the wet condition. The greatest difficulty, in constructing this apparatus, was in getting it absolutely water-tight, under the pressure exerted, when the tube is full of water. A very slight leak will destroy the results; as it is necessary to maintain the column of water, undisturbed, for many hours, in separating the finer clay materials from each other. The first experiments were conducted, by the use of a mixture of quartz sand, mica and clay, the sand and mica being of two grades of fineness; one, comprising that, which, while it passed through a 30-mesh sieve, was caught on a 40-mesh sieve, and the other, that, which passed through a 60-mesh sieve. The clay was ground, until it had all passed through a 1oo-mesh s1eve. At the first trial, these materials were remarkably well differentiated from each other. TESTS OF THE BEHAVIOR OF CLAYS WITH REFERENCE TO WATER Tests, along this line, have been made by the writer, for the purpose of throwing light on the nature and cause of some of the properties of clays. They are continued, in a modified way, for the more exact determination of such properties as have an economic bearing. In order to ascertain the water-absorptive power 1 An ordinary soap-shaker is Yery suitable. 45 of clays, and the shrinkage, on drying, of a self-saturated clay, dried samples \Yere taken, which had been ground and passed through a roo-mesh sie\e. The method employed was as follows: - Tin moulds were made, four and one-half inches long, by two and one-half inches \\ide, by one and one-half inches deep. the bottom being made of perforated tin.' These \\ere then filled with clay, by gently pouring it into the mould, obtaining, as nearly as possible, Fig. 3 the same densities, \Yhich were, how ever, determined in each case. After obtaining the weight of clay, by difference, the filled moulds were placed in a broad, leYel-bottom pan, containing water, rising just to the level of the clay in the moulds, a wide pan being necessary, in order to feed to the clays a sufficient amount of "ater, without materialh altering its leYel. \Vhen the moulds, filled with clay, are exposed to the water, there is a striking difference in the behavior of different samples, some taking much \'essels for \Yaler-absorption Tests, Etc. more water than others. The first effect, noticeable, is the down-pull 2 of the clay, the moment it is touched by the water, causing a vertical shrinkage, varying from almost nilzi! to nearly 50 per cent., and varying with the absorptive power of the clay, and with its clensit\. Following 1 See fig. 3. 2 Clay dried from the wet state, will, however, of course,exp.and on being a5ain wet, this question. depending ultimately on density. PROSPECTING AND TESTING the first down-pull, broad cracks form in the clay, sometimes one..eighth of an inch, or more, across, which are persistent, no matter how much water the clay absorbs; so that it becomes necessary, for further experiment, to slightly stir the whole to a homogeneous mixture. Such cracking is evidently due to the more rapid rising .of the water along the sides, whence it penetrates the clay laterally, causing the cracks, by the shrinkage produced. The results of a number of such absorption-tests are grouped in a table, further on. The samples are removed from contact with the water, at the end -of twelve hours' exposure, though, in practice, they are found to gain little, if any, after an hour's exposure; the water, adhering to the bottom of the vessel, is removed; the whole is immediately weighed; and the weight of the water, absorbed, is determined, by -difference. By use of this method, clays are found to absorb .amounts, ranging from 2 5 to 200 per cent. of their own weight. SHRINKAGE The samples, from the above process, are then allowed to air-dry, this being facilitated, by use of the steam-bath, in some cases. when perfectly dry, the shrinkage is determined, by difference, between the inside measurements of the moulds and the dimensions .of the resulting brick. Under these circumstances, shrinkages have been noted, running as high as 30 per cent. For the determination of the shrinkage of clays, on drying, from the practical standpoint, that is, under such conditions as are employed by brickmakers etc., small bricks were moulded, enough water being added, in each case, to make the clay thoroughly plastic, and marks were made near the edges of the brick, and on three sides. The distance between such marks, on the respective faces, were carefully measured, before and after drying, the difference giving the shrinkage. Such shrinkages vary from one to ten, and PROSPECTING AND TESTING 47 .average about eight per cent. It is impossible, to obtain accurate, comparative results, with this method, because of the difference in obtaining like results, and because of the necessity of using differ-ent quantities of water, to obtain the required plasticity, with different kinds of clays. DETERMINATION OF THE DEGREE OF CONSOLIDATION OF AIR-DRIED CLAY Since the strength of air-dried clay is an important factor in the manufacture of many clay products, it is deserving of attention among laboratory tests. It may be determined, in a variety of ways. Sticks of dried clay may be suspended by the ends, and the weight, which they will support without breaking, be ascertained. The crushing strength may be determined, as is done in the case of building-stones, bricks etc., by moulding the clay into cubes, and testing them in an ordinary crushing-machine. The resistance to penetration, by a needle or cone-shaped instrument, like Vicat's needle, used in testing cements, may be determined; or the tensile strength may be ascertained, by making brickettes in a mould, similar in shape to that of fig. 3, b, and testing with a tensile strength machine; also, of the kind, used in examining hydraulic cements. METHODS OF DETERMINING PLASTICITY The capability of being moulded, and of retaining any given shape, possessed by a mixture of clay and water, as has been shown in the description of plasticity, varies, according to a number of factors. For all practical purposes, it can be satisfactorily determined, in a direct way. A few experiments, made in as many minutes, will give the approximate amount of water, required to produce the maximum plasticity, which. it should be remembered, PROSPECTIKG AND TESTING is only the possibility in the substance of internal re-arrangements, sufficient to allow the whole to be modelled, while, at the same time, its rigidity is more than sufficient, to resist collapse or distortions, which gravity tends to produce. Any observer, of common-sense, can thus experiment with clay and arrive, very closely, at its limitations, with reference to its capacity to take and retain, while drying, such shapes as are commonly required in the manufacture of clay products. At the same time, its amount of shrinkage can be closely estimated, and degree of consolidation, noted. For purposes of comparison, and in the hope of obtaining some accurate and scientific results, experimenters have suggested, from time to time, various methods of procedure. Bischof, who was an eminent German investigator and the author of a work on Fire-clays,1 made a number of suggestions. One was, that a standard series be adopted, and comparison of other clays made with these, by noting the relative amounts of clay rubbed off on sheets of paper, the rubbing being done with the fingers. Another suggestion was, for a comparison of water-absorptive power of clays, based on the theory, that the more water a clay absorbs, the more plastic it is; and still another suggestion, by this author, was, that comparisons be made, by forcing pencils of the moistened clay samples through a die, in a horizontal position, and noting the rigidity, by measuring the maximum distance, in a horizontal direction, reached by the pencil, from the die. Another method of expressing the plasticity is, by means of the tensile strength of the dried clay. This was tried by the writer, in the preparation of a Ph. D. thesis, at Harvard, in the winter of 1893-'94 Of these methods, only two deal directly with the question of 1 D:e Feuerfesten Thone. Leipsic, r876. TilE CLA l"S OF GEORGIA PLATE IV f'ROSPECTJXG AXD TESTJX(; 49 plasticity; the others are the determinations of properties, essentially different from plasticity, and result, either from the confusion of properties (which seems to be the case), or the assumption, that the variations in t\\o properties are constantly the same; and, if this is the assumption, it does not seem to be justified by facts. One of the direct methods is that, recommended by Langenbeck,' that is, the penetration test, by the usc of Vicat's needle. But, in his application of the principle, he assumes, that the greater the plasticity of a clay, the larger the amount of \\ater, needed, to bring it to a definite degree of softness, at which it can be \\orked. He says:-- "In order to determine this point, an apparatus has been de\ised for pushing \Yith a fixed load a wire rod, or thin-walled cylinder, to a certain depth, within a certain time, into the softened clay. "The proportion of water, required to soften I oo parts of the dry clay, to the requisite emollescence is t::tken, as the direct measure of the plasticity." This method has certain advantages, when confined to the obtaining only of comparative results. But, according to the writer's experience, if employed, as it apparently is by Langenbeck, in the examination of all classes of clays, it is capable of leading to errors. For example, some slightly plastic clays would, \\hen little water is added, be almost as incoherent, as in the state of dry powder and would readily suffer the maximum penetration of the needle. Upon the addition of more water, they would reach their maximum toughness and plasticity; but, upon further addition of water, they \\"Ottld become rapidly softened, or fluid, in nature, and again, be readily penetr::tted by the needle. There seems no reason, why it should not be employed, for the purpose of determining so PROSPECTING AND TESTING maximum toughness; and it has the advantage of measuring, in a way, both the important factors of plasticity. The other direct method is that of Bischof, where the mixture of clay and water is pushed through a small cylindrical tube. This method, like the one just discussed, is capable of gi"Ving positive results, the only requirement being, that a number of tests be made, with each clay, using different amounts of water, in order to obtain the maximum plasticity of each. Of the methods, which have been employed by the writer, that of tensile strength of dried clay, as furnishing an index of plasticity, was abandoned, for reasons which will be explained later; but it has been used, for direct determinations, with wet clays. Tin moulds were used,' which had the perforated tin bottom, and were large enough at the center, to give a one-inch crosssection of wet clay. From this central portion the sides of the mould expand toward the ends, the whole being about three inches in length. The clays are weighed and allowed to absorb water, just as in the case of the absorption tests; they are then dried to different stages of wetness, and submitted to the tensile-strength apparatus. On account of the lining of filter-paper, the wet clay is readily removed from the mould; but, in most cases, it is too fluid, in the state of saturation, and must first be partially dried, when the diminished cross-section must be taken into account. This method usually permits of the ready determination of maximum plasticity. An adaptation of the penetration principle has, also, been tried. Experiments have been conducted, by means of the apparatus, illustrated in fig. 4, which consists of balances, suspended by a pulley, so as to be raised or lowered to any required elevation, supporting, 1 See fig. 3, b. 1'/WSl'ECTIXC A.\'D TFSIf,\'C 5 I at one end, a pan with weights, and, at the other, a steel-tipped plumb-bob, carefully turned, so that opposite lines, running to the point, include an angle of 40. The weight-arm is constructed, by a thread, passing through a pulley with an index finger, mov1ng .on a scale measuring degrees of a circle. In some expenments, this plan was Fi~. 4 modified bv attach- 1ing a mirror to the weight-pan arm, \\'hi c h reflected a beam of light upon a vertical scale. The operation 1s I .h~ performed, by bring- ring the clay beneath the plumb-bob, the balance being clamp- eel to prevent swing- ing. The balance is Apparatus for \.Jsc in Plasticity Experiments. then lowered, until, while the arms are still horizontal, the point of the plumb-bob just touches the clay. when the balance is undamped, a weight, is very gently removed from the pan, and the plumb-bob is allowed to settle in the clay for one minute. In all the experiments in each of these senes, the same weight of clay is taken, and the vessels used, are identical in shape and s1ze. \Vhen possible, a 200-gram weight is removed from the pan; but, in the case of the low-strength clays, it is necessary, to remove but roo grams, and sometimes only 50. The number of grams PROSPECTING AND TESTING removed is recorded; and, of course, it should be observed, in com- paring the relative strength of the clays. In addition to these, an original method was tried, by means of an apparatus, devised to test the tensile strength of clays, at different stages of wetness, up to and including that of self-saturation. The requisites for the apparatus were, that it should permit the absorption of water by different clays, under uniform conditions, and should be so constructed, as to grasp, in some way, very wet clay, and prevent, as far as possible, any flow, or change in cross-section, Fig. 5 Apparatus for Testing the Tensile Strength of \Vet Clays. while the breaking test was being made. The apparatus, found to best fulfill these requirements, is illustrated in fig. S It consists of two rectangular metal cars, with perforated bottoms, like the moulds above described. These cars have a cross-section, one inch wide and one and one-eighth inches high, and are about four inches, each, in length. The extra depth of the car is to allow approximately for the shrinkage of the clay powder, when wet, so that the final cross-section of the wet clay may be, as nearly as possible, one inch square. On the open ends, are flanges, a quarter of an inch wide, where the cars join. \Vithin each car is soldered a test-tube I'ROSJ'ECTIKG AKD 7ES7LYG 53 :brush, placed horizontally in the center of the car-box. These brushes are cut off, about a third of an inch from the open end of the car, and are slightly tapered at that end. An end view of one . of these cars is shown in fig. 6. One is mounted on clock \\heels, so as to run, with the least possible friction, and is connected \rith a pan, to receive weights, by a cord, \rhich passes over a pulley- ,wheel, at the level of the .center of the car. The other Fig. 6 .car rests upon wire legs, and ,js attached firmly to the ta- .blc, which supports the ap- paratus. \\'hen ready for usc, the .open ends of the two cars are brought together, being separated by a thin piece of .felt, cut to fit the flanges on the ends of the car, and are ;held in place by means of clamps. The bottom is lined with filter-paper, to prevent the escape of clay through End View of a Part of the Apparatus for Testing the Tensile Strength of \Yet Clays. the perforations. The apparatus, thus prepared for usc, is filled with dry, powdered clay, gently sifted1:into the cars, \rhich arc jarred sufficiently to insure the complete penetration of the clay .among the bristles of the brushes. After weighing, and ascertain- ing the density, it is placed in a pan of water, so that the surface .of the water just reaches the clay through the perforations. \\'hen .the clay has absorbed its maximum amount of water, the apparatus .is returned to its position on the table, the clamps are gently re- ~. l 54 PROSPECTING AND TESTING moved, and weights delicately, but rapidly, added, until the wet clay breaks, and the two cars separate. It is probable, that better results might be obtained, by substituting, for the weight-pan attachment, a spring apparatus, which. could be connected with the movable car, and which, on being pulled, until the cars separate, would automatically register the required strength; or, by using the cement tensile-strength apparatus,. as in the case of the dried clays. OBJECTIONS TO THE INDIRECT METHODS The objections to the indirect methods are, first, that it has not been shown, that the variations, in the properties actually tested, are in constant ratio with those in plasticity; second, that, in the preparation of the samples for testing, or in the process of conducting the experiment, the "personal equation" is as large, as in the simple, hand examination of the clay-worker; and, tlzird, that the results, attainable, have so large a limit of error, as to be insufficiently accurate, for scientific purposes. The dry tensile-strength test is based upon the assumption, that the plasticity of a clay is due to the interlocking and interlaminating of plates and bundles of prisms; but this involves a misconception of the nature of plasticity, as already shown. Moreover, according to the writer's experience, there is no constant relation,. between the properties of the clay, in the dried and wet states. As an illustration of this fact, experiments, conducted on two different clays, will serve. One of these is from Woodbridge, N. ].,. and is a soft, "plastic" clay; the other, a sample of the Christy washed pot-clay, from St. Louis, Mo. The accompanying table: shows the important facts:- FROSFECTJKC A_\'D TESTJXG 55 ,---Name of Clay-~ Woodbridge, N. J. Washed Clay, St. Louis Amount of Clay Base______ 9434 56.13 " " Sandy Impurities 1.92 38.32 Percentage of \Vater Absorbed _________________ 75.00 52.00 Tensile-strength Units, in Sat- urated Condition ________ _ 6o Tensile-strength Units, 7:3' of Absorbed Water Evapo- rated ___ --------- ____ 330 Tensile-strength Units,% Ab- sorbed \Vater Evaporated_ 6,8go 68 320 I ,800 Tensile-strength Units, Dried Condition _______________ _ 4,200 Shrinkage on Drying _____ _ r6 10,300 rg A study of this table shows the hopelessness of measuring the plasticity of clays, by their tensile strength when dried. \Vhat is shown is, that the Christy clay has about 20 times as much sandy impurity, as the \Voodbridge clay- in fact, more than one-third of it consists of quartz sand. It absorbs less water; it is less plastic, by the direct-weight tensile process, having a maximum of about one-fourth of that of the \Voodbridge clay; and it has a greater shrinkage. But, by the dry tensile test, it is more than twice as strong as the \Voodbridge clay. _By this method, then, it is more than twice as plastic as the \\'oodbridge clay, an absurdity and a contradiction of facts. Besides the results shown in the table above, experiments, made with the penetration apparatus, showed, that the ease of penetration of the two clays, the \Voodbridge and the Christy, in a state of saturation, 1s in the ratio of Go to 57; but, when the same quantity of water is ad dec! to each, the amount taken being the average of the amounts required to 1 'i E'ROSJ'FCTIJ\'G AND TEST/X(; produce a maximum toughness in each, they sho\Yed the ratio of case of penetrability of C) to 25; or, in other \\ords, that the \Yoodbridgc clay, under certain similar conditions of \Yetness, is more than two and one-half times as tough or rigid as the Christy clay. The last objection to this method, that is, that it is insufficiently accurate, for scientific purposes, is borne out by the admissions of one of its champions, frst, that a large "personal equation" comes in, in preparing the sample; and second, that one, without considerable experience, in employing the method, will get variations in results, of from 2 5 to :;o per cent. of the strength of each clay: and that the expert can only hope to keep the variation to within 20 per cent. SUl\DIARY OF RESULTS The experiments, conducted with reference to tltc bdlfrzior ol dt7J'S tocz,ard water, showed, naturally, results, widely varying among different clays. A brief summary of the more important of them is given bclow:- Clays absorb water, in amounts, varying, respectively, from 40 to 200 per cent. by weight. 2 Generally speaking, those, which were originally incoherent in nature, absorb the largest amounts of water: and, with little ,ariation, the less the dmsi!J' of the dried, pulverized clay, the higher the percentage of absorbed water. 3 The rate of drying varies directly \\ith the amount of water absorbed. 4 The amount of slirinlm,r;c of a clay varies according: to a complex of conditions, such as density, the size and shape of particles THECLA YS OF GEORGf A PLATE V NCONFOR~IITY IH:TWEEN SANOY CLAYS, IN A CUT ALONG THE GEORG IA RAILROAD, NEAR AUGUSTA, GEORGIA. l'RO.\'J'ECT!Xc,' AX!J TFSTll\'G 57 .0 f the clay-base, and their state of aggregation;' also, according to the amount of sand present, and the size and shape of its particles. 5 The percentage of secondary shrinkage Yaries in different directions, being /7(t7/cst for the smt7llcr dimtnsions, the reason for this being, probably, as follo\YS:- The tendency to establish equilibrium in the mass, due to the loss of water on an evaporating surface, is not followed by uniform results, O\\ing to greater friction, and a greater amount of mass, to be moved in the longer direction than in the shorter. Consequently, the movement and shrinkage is more successful, along the shorter dimension. J\Iore marked than this, however, as a cause, is the difference in the amount of friction, on the contact surface, at the bottom of the brick, along the lateral and longitudinal directions. A slender pencil of clay can be dried, without breaking, only by resting it on a series of rollers, or by some similar de\ice. G The tenacity of the clavs varies exceedingly, at different stages of wetness. 7 In general, clays, diminishing the most in bulk, through sec- ondary shrinkage, were, in the dried state, the most tenacious. For example, one clay, having a maximum shrinkage, in a single direction, of about 24 per cent., withstood a strain, per square inch, eleven times greater than another with a maximum shrinkage of less th;m 8 per cent. 8 l'lastici ty depends upon the amount of water present; on the ;,hape and size of the particles; and on the attraction of these for .water. 1 The kaolinite :-;cales arc sometimes grouped togdhcr into lar~er units. ss FROSFECTJXG A.A"D TESTL\;G EXPERDIENTS ON THE BEHAYIOR OF CLAYS WITH REFERENCE TO HEAT The effect of heat on clays is to drive out the combined water; to change the color (when certain impurities arc present); to consolidate, and, ultimately, to fuse them. The experiments, necessary to determine the valuable qualities of a clay, are to burn them to different degrees, noting the color, structure and strength of the burned product, and observing the amount of shrinkage suffered; and to observe the temperatures, required for burning to a desired hardness, and the point, at which fusion takes place. The burning tests are made, very conveniently, in an ordinary muffle furnace. The determination of fusibility, especially for the more refractory clays, requires the use of specially devised apparatus, and some instrument for determining degrees of heat, over as great a range of temperatures as possible, and the means of obtaining comparative results of temperatures, too high to be measured by any instrument. This recording of the higher temperatures is known as pyrometry, and a great variety of methods have been employed, by different investigators. A comprehensive study of the measurement of high temperatures will be found in a bulletin of the United States Geological Survey, by Dr. Carl Barus; 1 and the application of various methods to the determination of the fusibility of clays has been presented, in a paper by Hofman and Demond.2 1 On the Thermo-Electric ).Ieasurcmcnt of High Temperatures. U.S. Geol. Survey, Bul. S-1-, b~-" Carl Barus. 2 "Refractoriness ot Clays. T1aas., .\.I. :-1. E . \'ol. XX!\', p. 32. 59 Of the many methods, which have been advocated, the most reliable and convenient, according to the writer's experience, is the Fig. 7 Illustration Showing !low Seger Cone' Are ltberted in a Brick-kiln, for Regulating Tetuperature. Segcr-cone method, and the German modification of Le Chatelicr'' pyrometer. 6o This pyrometer consists of a hard porcelain tube about a yard long, within which is a thermo-electric coupling, of platinum and an alloy of platinum and rhodium. This tube is inserted in the fire, where it can l>e left or removed at will. The coupling is con- nected, by insulated wires, with a gahanometer, the deflection of which is recorded on a dial, by degrees of temperature. This in- strument records temperature, up to r ,600 C. Fig. S The Se<,.,rer- cone method is one which was propos- ed and dcvcl- oped by Dr. Scgcr,of Her- lin. lie pre- pared a series of \cry point- ed three- Illustration Showing I low Seger Cones Are lnserle-, ' ', ,,'' LEGEND F111/ Line ~ Building Brick, Fire Brick and 0 } --- Sewer Pipe Work.t. X 0 ...f0ol / '!filu . ( JO Map lndi cating th e Clay Deposi ts and Cte Location of the Clay ln dustries along the South ern F .lll-Line in Georgia. CEOLOG Y AND PJJYSJOCRAl'HY 8I the Cretaceous strata, eastward, across the State, thus necessitating a modification of the geological map of Georgia, which has hitherto limited the Cretaceous to a strip of territory, traversing the central western part of the State. Second, the di'scovery of white kaolin, some of which ranks with the valuable South Carolina deposits, as "paper clay." Third, the experimental proof, that some of these kaolins, suitable for fire-clay, are more refractory, than any of the noted fire-clays of the United States. GEOLOGY AND PHYSIOGRAPHY East and South of the Appalachian mountains, which consist of folded Paleozoic strata, extends the so-called Piedmont Plateau, consisting mainly of ancient metamorphic and eruptive rocks. This "plateau" is a northeast and southwest trending belt, having an undulating or rolling surface with hill-tops lying, almost uniformly, in a theoretical plane, which dips away toward the sea. Bounding this area, on the seaward side, is the Coastal Plain, which differs widely from the Piedmont Plateau, in the nature of its rocks, in age, and in general aspect. The rocks here are sedimentary, and range from Lower Cretaceous to Pleistocene. The Metamorphic schists and gneisses of the Piedmont Plateau are crumpled and distorted; and the beds, if they may be called such, appear to stand edgeWise. On the upturned edges of these rocks, are the almost horizontally lying, sedimentary strata, which make up the Coastal Plain. The boundary line, or the surface line of contact, between the Coastal Plain and the Piedmont Plateau is known as the Fall Line. Owing to the different geological conditions in the two re- 82 GEOLOGY AND PHYSIOGRAPHY gions, the rivers, traversing them, undergo a great transition 111 character along this Line. They cross the Piedmont Plateau, swiftflowing, often as cascades, and, still more frequently, as dashing rapids, the water tumbling over hard ledges and boulders of crystalline rocks. But, emerging from the gorges and comparatively deep valleys of the Piedmont belt, they begin a quiet, meandering journey, over the Coastal sediments, to the sea, the larger rivers becoming navigable at the Fall Line. A study of the geological map of the United States will show, that, from New York southward, almost all the large cities are situated along this Fall Line, that is, along the \Vestern margin of the Coastal Plain. In Georgia the important cities, so located, are, Augusta, Macon and Columbus, at the head-waters, respectively, of the Savannah, Ocmulgee and Chattahoochee rivers. The topography, or surface features, of the Piedmont Plateau has resulted from forces diametrically opposite, in large measure, to those, which have outlined the surface features of the Coastal Plain. In the case of the former, the operative forces have been destructive; in the case of the latter, they have been largely constructive, and in part only, destructive. The present surface of the Piedmont Plateau has been attained by the removal of a vast thickness of overlying rocks, and is, we know not how much, lower than the original one. The rocks, of which it is composed, were once probably largely sedimentary, or water-deposited. They were traversed and overflowed by masses of igneous rock; and all have been so modified by the forces, which have acted on them, in the long interval of geologic time, since their formation, that their original nature is largely lost, and they have passed into the category, known to geologists as Metamorphic rocks. They are composed largely of quartz, feldspar and mica; and they are cut by in- numerable quartz veins. These rocks, through the action of the atmosphere and surface waters, are constantly decomposed, and the rain and the streams are carrying the decomposed products to the sea. The diHerence between the rate of decomposition of the rocks and the rate of removal of the products, results in the surface zones, -soils at the top passing downward through less and less decomposed material, to the solid rock below, the latter being frequently stripped bare, and exposed in gullies and stream-beds. For a long time, even for a long geologic time, this process of lowering the surface of the crystalline rocks in the Piedmont belt, and the giving up of its material to the sea, took place, while the margin of the sea was far inland, with reference to its present position. The seashore may be considered to have been approximately along the line, which has been defined as the Fall Line. The products of the weathering and decomposition of the Piedmont crystallines, consisting of clay, sand and gravel, of varying coarseness, were emptied by the streams and rivers into the sea, and \\ere distributed according to varying conditions. They finally built, along with the limestones, which were formed, the stratified beds of the Coastal Plain. These consisted, besides the limestone, of clays, mz >....; NOTES BY LOCALiTIES 121 broken up and much slickensided, is exposed along the entire slope. It is at least 100 feet, in thickness. This bed of Tertiary materials rests unconformably on the "chalk," or Potomac clay, at the base. As mentioned before, the outcrops of the "chalk" are to be seen in gullies, in the lowlands, for miles around. At a distance, where the soil has been washed away, the effect is like that of snow-fields. The roads, too, are often colored white, by this material; and they make remarkable contrasts along-side of the red, vermilion and yellows of the sands and other clays, which are usually associated with it. The white clay, in these localities, is often entirely free from grit and sand particles. It is sometimes plastic and sometimes non-plastic, in the latter case, weathering into angular fragments. That, exposed on the Massey property, weathers and crumbles into dust. In other places, it becomes exceedingly hard on exposure, and rings under the blows of a hammer. This latter variety is characterized, when powdered, by a mealy, instead of the ordinary unctuous, feel. It contains, however, what seem to be nodules of a slightly different clay, as has been seen and noted at other localities. These so-called nodules are dark in color, and plastic. They are found in pear-like shapes, with slender necks, and look something like Prince Rupert drops, the largest part being nearly always the lowest. In places, this clay contains much iron, which is particularly common on the jointed surfaces, but which is sometimes contained in the clay, as aggregations of ochre. The occurrence of red ochre is specially abundant on the property of Mr. N. A. Whitehurst. On the north side of this ridge, the bluish clay, which overlies the white Potomac clay, is probably the same as that, exposed on the road-side, west of Mr. Baker's house, as described above. 122 NOTES BY J:OCAUTIES Samples of this clay, for lab01:atory purposes, were taken from four different localities. One of these may be described, macroscopically, as being a massive, fine-grained, white to buff-colored clay, which glistens brightly in the sun-shine, the light being reflected from numerous mica scales. l'\ o quartz is to be seen, under the hand lens. It absorbs water rapidly; and, when wet and moulded with the hand, no grit is felt. Under the microscope, a multitude of scales and prisms of muscovite appear, 99 per cent. of which arc exceedingly minute; but a few scales range, in diameter, to .003 of an inch. Quartz seems to be absent, and magnetite crystals are very rare. It varies in specific gravity, from 1.75 to I. 8 5. Briquettes shrink, on drying, less than one per cent. in length; and they have a tensile strength of 2 3 pounds per square inch. On burning, no further shrinkage is observable. It burns white, or to a fine pinkish color, crackling more or less intensely, according to the nature and temperature of the flame, to which it is exposed. \Vhen burned carefully, it makes a smooth, porous, substantial brick, with only a faint tendency to crackle. Its fusing point is between Seger cones 3 5 and 36. Another sample, taken a half-mile west of the locality, from which this clay was collected, has practically the same characteristics and properties, as do two other samples, selected at points half-a-mile apart. The fourth sample, spoken of above, resembles these in the hand specimen; but it contains, scattered throughout, round areas of another clay, slightly rusty in color, some of which are at least two-fifths of an inch in diameter, although they are usually smaller. This clay does not rapidly absorb water; and it requires considerable rubbing, before an emulsion is obtained for microscopic study. A high power shows considerable foreign matter, varying in size KOTI:S RY LOCALITiES 123 up to .005 of an inch. This mineral is remarkable and unusual. It occurs in little prismatic crystals, \\hich are sometimes straight, but often curved into semi-circles, or more complicated forms. Such crystals have a black border, and show a rather high single refraction; but the double refraction is very weak. They range in size from mere specks, which cannot be measured, up to .ooo6 of + an inch in diameter, .0003 3 being, perhaps, the average size. In color, they are usually gray, with a faint yellowish tint. Similar bodies have been described by Ternier.' They have been noted in Missouri clays by Haworth, \Vho identifies them as prochlorite. Those, which he describes, have a cleavage at right angles to the prism; while these have a cleavage parallel with the prism. The small rounded areas, spoken of, seem to differ from the rest of the day, in that these worm-like b?dies are less abundant and smaller. The clay, as a whole, is remarkably free from quartz grains; but it contains occasional needle-like crystals of rutile. A sample from a hundred-foot bed of clay, of which the mass of the hill is here constituted, appears in the hand specimen to be finegrained, massive, friable, and locally spotted with stains of iron oxide. No trace of foreign matter is revealed with the pocket lens. It absorbs water rapidly; becomes extremely plastic; and shows no traces of grit. Under the microscope, with a No. 3 objective, the only foreign matter appearing is an occasional scale of muscovite, or a grain of magnetite. ]\' o other impurities are revealed by a high power. It varies in specific gravity from 1.82 to 2.00. It shrinks, on drying, 9 per cent., and, on burning, an additional 2 per cent. It burns white, without crackling. 1 See Compte Kendus, T, C\-lll, 1SS9, p. I,07I. 124 }.;QTES BY LOC'ALJTIES THE R. S. S:\IITH PROPERTY On the east side of the road, and just opposite the :Massey property, on the estate of Mr. R. S. Smith, there are good exposures of the Potomac clay, as is also the case, on the adjoining property of Messrs. Smith and Sons. A sample, from the latter place, shows a white, fine-grained, friable clay, specimens from near the surface being more or less stained with iron oxide. Under the lens, practically no quartz or mica is visible. A microscopic examination proves it to be a remarkably pure clay, the only foreign matter being exceedingly small prisms of muscovite, and a few specks of magnetite. The largest of the muscovite scales are .001 of an inch in diameter. Briquettes of this clay shrink, on drying, 8 per cent. of their length, and, on burning, an additional 2 per cent. Its tensile strength is 5 I pounds per sc1uare inch. Its specific gravity varies from I. 55 to r.66. It burns, without crackling, to a cream color; and its fusing point is very high, standing between that of Seger cones 35 and 36. LOCALITIES SOUTH OF THE MASSEY PROPERTY Traveling south and southeast from the Massey property, all the way to Big Sandy creek, which flows in an easterly direction south of Irwinton, the white Potomac clays are frequently seen in the valleys and low lands. The overlying Tertiary strata become thicker, however, as the Fall Line becomes more remote, until finally the streams fail to cut through them, and these clays remain NOTES BJT LOCAJJTJES 125 hidden from sight, though they doubtless continue easterly and southerly far out beneath the waters of the sea and the gulf. Samples of clay were taken from the banks of the Big Sandy, and from the properties of Messrs. Vincent and Bridges and Mr. Z. T. Miller. THE Z. T. MILLER CLAY The Miller property is situated about a mile, or a mile and a half, south of the Massey property. The road approaches it, by descending a steep slope, where a bed of fine clay, I 20 feet thick, similar to those described at Massey's, is exposed, overlaid by orange and vermilion sands. Unconformably underlying it, is the Potomac clay. This is exposed on the Miller estate, in gullies, and at the surface in low-lying fields. The thickest exposure, yet seen, is at this locality, where at least thirty feet of the white clay is visible. It is remarkable, here, for the abundance of the pearshaped cavities and areas, which have been spoken of above. These would seem to have originated, by the boring of worms or insects, were it not," that they permeate the whole mass, throughout its thickness, and yet do not seem to be connected, one with another. This clay is also noteworthy, on account of a property, it possesses, of hardening, on exposure to the atmosphere. Often, for several feet beneath the surface, it is exceedingly hard and tough, and is penetrated by a pick with difficulty. This property leads to a considerable use of the material, in the construction of chimneys. The soft clay is trimmed into blocks with an ax, and exposed to the weather, whereupon, they become hard and strong. Nothing, revealed by the chemical analysis, or the microscopic examination, explains 126 NOTES BY LOC'ALITIES this phenomenon, which may result, however, from the deposition, on drying, of an exceedingly thin film of soluble silica, among the clay particles. A hand specimen, from the average sample collected, is creamcolored, very fine-grained and friable. The cavities, spoken of, have occasionally a dark lining of a carbonaceous material; and this suggests, as a possible explanation of their occurrence, that they originated by the decomposition, and removal by solution, of organic remains, either animal or vegetable. \Vith the hand lens, neither quartz nor mica are discernible; and, under the microscope, no quartz can be distinguished; while muscovite is of extreme minuteness, and rare. A chemical analysis of this clay gave the following results:- Hygroscopic :.Ioisture. . . . . . . . 0. 2 I Combined Water, Carbon Di-oxide Etc. Combined Silica . . Free Silica, or Sand . Alumina ... Ferric Oxide . Potash Lime Soda . Total I4. 52 42.79 .82 40-42 -70 trace 00.37 .83 . I00.45 Clay Base Fluxing Impurities 97 73 I. 90 This clay absorbs So per cent. of its weight of water. Its specific gravity ranges from r.Sg to 1.94. Briquettes shrink, on drying, 8 per cent. of their length, and an additional 4 per cent., on burning. They have a tensile strength, dried, of less than I o pounds per square inch. It burns snowy white, with a strong tendency to c\'OTES BY J:OCAJJT!ES 127 crackle. Its fusing point is very high, nearly equal to that of Seger cone 36. THE YIXCE~T .\XD BRIDGES PROPERTY This property is one mile south of Irwinton. Clay occurs here, in much the same manner as at Miller's. It is massive, fine-grained; and, under the lens, it shows only a trace of muscovite. The microscope shows it to be one of the purest of clays. Quartz grains are very scarce. Mica, however, appears, though in small quantity; and magnetite cannot be detected. Briquettes of this clay shrink, on drying, about 9 per cent. of their length, and, on burning, an additional 4 per cent. Its tensile strength is 28 pounds per square inch, and its specific gravity varies from 1.64 to 1.73. It burns to pure white; but it cannot be utilized alone, on account of crackling. Its fusing point shows it to be one of the most refractory of clays, nearly equal to that of Seger cone 36. THE BIG SANDY DISTRICT Irwinton, the county-seat of \Vilkinson county, is separated from Jeffersonville, the county-seat of Twiggs county, by a valley, fifteen miles broad, which is drained by Big Sandy creek. The two towns stand on ridges, of practically the same elevation; and the low land between them is much broken and dissected. The two clay localities, last described, are typical of the many "chalk" deposits, found in this low-lying district. On Big Sanely 128 NOTES BY LOCALITIES creek, the clay has a thickness of twelve feet, the lower six feet being almost white and free from grit. The upper part of the bed is sandy and drab-colored. Overlying it, is a bed of mottled purple-and-red clay. The white variety is very hard and brittle, resembling flint, though not so hard. It can be scraped with a knife into a soapy-feeling powder. A hand specimen from an average sample of the white clay is fine-grained, compact, and breaks with a conchoidal fracture. It absorbs water quickly; but little clots seem to remain unaffected. Under the microscope, a low power shows, rarely, a small quartz grain and an occasional muscovite scale. A high power reveals only the invariable accessories- scales and prisms of muscovite. Briquettes of this clay shrink, on drying, 6 per cent. in length, and an additional 3 Yz per cent., on burning. Its tensile strength, dried, is 21 pounds per square inch. Its specific gravity averages 1.66. It crackles slightly, on burning, and retains its white color, which becomes creamy, in an intense heat. It has the same high refractory quality, as that at Vincent and Bridges, and other localities. THE MciNTYRE LOCALITIES The southwest limit of the outcrops of the Potomac clays passes Irwinton, in a northeasterly direction. Mcintyre is situated on the Central Railway, about half way between Gordon and the Oconee river. In its vicinity, there are again exposed, in the low-lying lands and at the bases of the hills, the red-and-white mottled clays, which appeared so abundantly, in the general region under discussion. The following section, in descending series, is exposed, in the nu- "\~OTic'S BY LOCAJJTI!OS 129 merous gullies, with vertical walls from 50 to 60 feet high, on the Irwinton-Gordon road, three and a half miles from :\Icintyre:- Red and Vermilion sands, massive, and without bedding-planes ________________ ------25 to 30 feet 2 Bright gold and yellow, extremely plastic clay, with thin seams of sand ______ ---~-~-- __ . ___ 3 3 Orange and white fine sands ----------25 to 30 4 \Yhite Potomac clays ______________ ---~ ___ _ 3 feet The laboratory examination of the yello\Y, plastic clay has not been completed. It is doubtless of Tertiary age. Two and a half miles northwest of 1\Icintyre, at the base of the eastern slope of a ridge, there is an exposure of about forty feet of white and somewhat sanely clay, in many respects closely resembling that on the l\Iiller property, the upper part being hard, and containing numerous areas of dark-colored, plastic clay, shrunken away from the walls of cavities. Above this, is a coarse fire-clay, overlying which are many feet of a characteristically faulted and slickensided fire-clay (the same as is described, in the notes on the Massey property), of reddish and purplish color. Overlying this fire- clay, are 6o to 75 feet of sands. The entire thickness of the section, exposed here, is I 70 feet. Just west of l\Icintyre, on the estate of Mr. L. A. Snow, are some outcrops of the Potomac clay, similar to other occurrences, except that, where exposed, they are somewhat discolored and sandy. East of Mcintyre, is a series of ridges and terraces, extending to the valley of the Oconee. The valley here is five miles wide, and largely occupied by low, rolling hills, similar to those in the Big Sanely valley. At frequent intervals, the chalk-like Potomac clay may be seen. On the John Davis farm, one and a half miles east of Mcintyre, 130 1\'0TFS lJ}' IOCUJ7JES it occurs with a thickness of thirty feet, the upper part being sandy. It is overlaid by a mantle, spreading down the slope of the hill, or ridge, of red and yellow Lafayette gravels, which contain numerous balls and boulders of the underlying clay. A.t the base of the section, the clay is almost wholly free from grit and sand; but it is largely stained with brilliant colors, red, yellow and purple. This clay would not be suitable for the demands of the paper industry; but it could be manufactured readily into paving-brick, pottery or sewer-pipe, there being plenty of fine sand, ancl, also, very ;Jlastic clay in the vicinity, making possible any required mixture. Beyond this exposure, is a broad, flat-topped ridge, maintaining the general elevation, as seen at Irwinton, Gordon and Le\\iston, and in the neighborhood of Griswolclville. Laboratory experiments with this clay show, that it absorbs water and disintegrates, readily. It shrinks, on drying, 5 per cent., linear measurement, and an additional 2 per cent., on burning. Its specific gravity varies from I. 73 to I .C)U; and it has a tensile strength, dried, of 21 pounds per square inch. It is apt to crackle, on burning, and it assumes a buff to fine reddish color. It fuses at about the same temperature as Seger cone 28. On the property of :\Ir. August Pennington, on the flank of this ridge, there is, also, an excellent exposure of the same clay, which again out-crops in the low land at "Chalk Hill," one of the foothills on the west side of the Oconee ri\Tr. The clay, at the latter place, where exposed at the surface, docs not indicate a high grade. It has a velvety appearance, is gray-colored, and contains some grit. In one gully, it is seen to grade downward into the sand. It contains, also, beds of red and yellow ochre, and is stained these colors, in many places. It contains, also, the pseudo-nodules, which have been so frequently referred to. ;H! TFS E Y J:OCJLJ'l'ILS I 3I An average sample, collected for laboratory study, shows that briquettes shrink, on drying, 4 per cent. in length, and an additional 2 per cent., on burning. Its specific gravity ranges from I.74 to I.90; and it has a tensile strength of 2I pounds per square inch. It burns, \Yith little crackling, to a fine pinkish color, at temperatures obtained in ordinary kilns. It is friable and easily broken, a fact, in general, of all these Potomac clays. On the Central Railway, a half-mile west of Mcintyre, a deep red, very plastic clay is exposed in a gully. Three feet of this bed can be seen; but it is doubtless much thicker. An average sample, examined under the hand lens, reveals the pearly-lustered cleavage faces of mica plates; and, under the microscope, magnetite grains become visible, the largest of \Yhich are .ooo6 of an inch in diameter. Quartz is almost wholly absent. Briquettes of this clay shrink, on drying, 5 per cent. of their length, and an additional 4 per cent., on burning. Its specific gravity ranges from I./4 to r.Ss. It is almost impossible to dry it, without crackling; and its tensile strength, dried, is, therefore, not satisfactorily determined. It burns to a deep-red color, and crackles. Its fusing point has not yet been determined. It is probably low, owing to the large amount of iron oxide contained. --- XOTES !JY LOCIJJT!ES LOCALITIES XEAR THE ::'llACOX A:'\D DUBLIX RAILROAD, TWIGGS COUKTY The northern half of Twiggs county \Yas carefully explored for l'otomc and other clays, characteristic of the Fall Line belt. In addition to trips from l\Iacon into this county, the dirt roads \\ere traversed, \Yith many side trips, from Griswoldville, south\Yesterly to Dry Branch, southeasterly, along the line of the l\lacon and Dublin Railroad; and thence southwesterly to Bullard's Station on the Southern l~aihYay, and in the valley of the Oconee. From Bullard's Station, practically all of the roads were traversed north to Dry Branch, again, \Yhich is on the boundary between Bibb and T\Yiggs counties. In this area, just as in the northern part of \Vilkinson county, there are abundant outcrops of Potomac clay, which disappear southward, under the overlying Tertiary strata. There are also some interesting clays, in the latter formation. THE PAY::-JE AND XI-<:UoOX CLAY PIT One and a half miles south of Dry Branch, and about half-a-mile northeast of the railroad, a bed of the Potomac clay has been worked by the firm of Payne and ~elson. The works, here, are of the same nature as those at Lewiston, except that operations are, at present, conducted on a smaller scale. The clay is taken from an open pit, and is classified and stored in drying-sheds for shipment. As at Lewiston, it is generally shipped in casks, although sacks are employed for this purpose to some extent. XOTFS Hl. !OCA/JT/FS I ,1) ,o) The stripping consists of from one to two feet of soil and gravel, and from two to six feet of the Potomac clay, which is stained with iron oxide. The total thickness of the clay is fifteen feet, the lower three feet varying from gray to drab in color, and being rather coarse and containing an abundance of magnetite crystals. The best of the clay is pure white, and resembles !lour in appearance. The one defect is the occasional presence of ferruginous stains, along the joint planes, which necessitates careful sorting, and the trimming of the blocks of clay. This clay disappears, in the neighborhood, beneath the Tertiary strata, which consist of finegrained, laminated clays, aheacl\ described, as occurring at other points. A chemical analysis gave the following results:- Hygroscopic f\Ioisture. Combined 1\'ater, Carbon Di-oxide Etc Combined Silica . . Free Silica, or Sand . Alumina ... Ferric Oxide . Lime .. ::\Iagnesia Potash Soda . Total I 3 39 4308 I. 94 40.63 I.OI o. r6 0.00 0. 27 Trace !00.48 Clay Base Fluxing Impurities 97-00 !.44 A hand specimen, from the average sample collected here, resembles the Lewiston clay. It is very friable, and varies from white to a pale-cream color. It contains an abundance of muscovite scales and some grains of magnetite, readily detected by aid of the hand lens. Under the microscope, a high power shows XOTFS Ill~ LOCAIJ7/ES it to be a very pure clay, containing rare grains of quartz and magnetite, along with the muscovite, which characterizes all these clays. Briquettes of this clay shrink, on drying, 8 per cent. of their length; but, on burning, no further decrease in size is perceptible. It has a tensile strength, dried, of from I 2 to I 5 pounds per square inch. Its specific gravity varies from 1.72 to 1.89. It burns white. and, sometimes, to a faint pinkish color, and shows the tendenc\ to crackle, observable in all the clays of this class. Its fusing point lies between Seger cones 33 and 36. THE DRY BRAl\CH. FITZPATRICK. "NAPIER'S ~llLL. BOND'S STORE AND Bl:LLARD'S DEPOSITS Going south from The Payne and Nelson Clay \\'orks, and following the railroad, a variety of Tertiary clays may be seen in the cuts and gullies. Striking occurrences are exposed in the railroadcut at Dry Branch, and along the highway at several places near Fitzpatrick. i\ half-mile northwest of Fitzpatrick, on the Hornsby road, there is an immense gully, where the following sections are seen, in descending series:- Yellow soil, grading downwards into red sand _____ ~ ______ ~ __ . __ ~ ~ _______ ~ I o to I 2 feet 2 Laminated clay_~ _ 5 3 Fine sand, with carbonaceous layers (2 to 3 inches thick)~- ------ ------------- ___ G 4- Grayish,laminatedcla\----~-- ---------- 4 XOTES Jl r IOC.IJJTJES 135 5 \\"hite to cream-colored clay, which dries to a hard, punky condition, is exceedingly tough, and can be cut and carved, to a remarkable extent, e\en \\hen perfectly dry. It breaks with a conchoidal fracture, and the joint planes are concentrically arranged. These are stained with iron oxide, and the bed is permeated with veins of greenish-colored sands __ ____ ____ __ r 2 feet 6 Green laminated clay, very plastic and containing black carbonaceous layers _____ _____ __ S About a mile \Yest of Fitzpatrick, in a gully, by the railroad side, the clays of the above section may also be seen, to good advantage. They contain here, as at many other points in this vicinity, a few small fossil casts. The white variety \\as sampled for analysis and tests. The result of the chemical analysis is as follows:- Hygroscopic l\J oisture 8.70 Loss on Ignition-Combined Water, C02 Etc. r r. 2..1- Soluble and Combined Silica. 5-1-39 Free Silica, or Sand . 6. 89 Alumina I-1- 6-t Ferric Oxide . o. 28 Lime . . . . 7.08 :Magnesia . . I. 7I Potash and Soda 4-23 Total . Clay Base Fluxing Impurities So. 2 7 I330 A hand specimen shows a white to grayish clay, with sometimes a yellow to greenish tint, and occasional stains of iron oxide along the joints. \Vhen dry, although exceedingly hard and tough, it cuts easily; and, when cut, it shows a smooth, glossy surface, which I 36 XOTFS h'Y IOC-/IJT!loS takes a good polish. In spite of its toughness, it IS porous and almost as light as cork, floating readily on \\ater, although, \Yhen placed in the water, it slowly moistens, becomes pasty, and, after a few minutes, sinks. Some scales of muscovite may be seen with the naked eye. The clay is not very plastic. Under the microscope, there appears a large amount of foreign material, perhaps from fifteen to twenty per cent., which consists largely of rounded grains of quartz, the largest being .or of an inch in diameter. Occasional magnetite grains occur, and also plates and prisms of muscovite and angular fragments of feldspar. There are also a few small areas of a yellow-colored mineral, which seems to be titanite, but which was not identified with certainty. In adclition to these impurities, there occur occasional fragments of an isotropic, colored mineral, most likely basal sections of biotite. The clay particles are more or less bound together, in little aggregates. Its specific gravity varies from o.go to I.20, averaging near the former amount. Experiments, with the dry, powdered clay, prove it to have an enormous absorptive-power, the clay taking up over 200 per cent. of its own weight of water. It shrinks, on drying, 2 5 per cent., linear measurement. A dried briquette shows an average tensile strength of 2 I 3 pounds per square inch. On burning, the dried brick shrinks an additional 6 per cent., and burns from a buff to a pale-yellow color, easily crackling and fusing, at a temperature of 1,330 C. At a comparatively short distance east of the above locality, and in the vicinity of Napier's Mill, the white Potomac clay is again encountered, underlying the Tertiary beds. A hand specimen from this locality shows a beautiful white, friable and fine-grained clay, containing an abundance of muscovite scales, with numerous quartz grains, which may be distinguished THE CLAYS OF GEORGIA PLATE XIV VI EW lf.LUSTRATI NG SOME METHODS OF CLAY TESTING. In the background, are brickettes, for tests of tensile strength, and shrinkage on drying and burning. On the s ides, are types of vessels, used in testing cl::tys and checking temperatures, in furnaces and kilns. In front, are the vessels and covers, used in testing the highest g-rade refractory clays. Behind these, are some, which have been through the test, and are now broken open, exposing the cones, some of which have been partially or wholly fused. In the immediatt foreground, is a series of Seger cones, after a test. The unfused cone, on the left, is one inch high . NOTES BY LOCALITIES 1 37 with the pocket lens. Under the microscope, muscovite, magnetite and quartz are all visible, with a low power. A high power shows further, only, that these impurities occur in great abundance. This clay shrinks, on drying, about 8 per cent., linear measurement, and but slightly more, on burning. Its tensile strength, dried, is 22 pounds per square inch. Its specific gravity varies from 1.70 to 1.8 5 It burns to a faint pinkish color, crackling slightly, and has a fusion point nearly equal to that of Seger cone 36. West of Fitzpatrick, and between there and Bullard's station, there is a similar occurrence of the Potomac clay in gullies near the foot of the hills. It is here best seen at the road-side, near Bond's store, where it is in all respects similar to that at Napier's Mill. Going east from Bond's store to Bullard's, one travels over the Tertiary uplands, and finally down steep slopes to the Columbia beds of the upper river bottom (Ocmulgee river). THE STEVENS' POTTERY LOCALITY Stevens' Pottery is situated in Baldwin county, on a branch of the Central Railway, running from Gordon to Milledgeville. It is so named, on account of the clay-manufacturing plant of Messrs. Stevens Brothers and Co., situated there. This firm is the largest producer of fire-clay and pottery in the State, and one of the largest producers of sewer-pipe. For a general view, see Frontisptece. This plant consists, in part, of one pipe-machine, one semi- NOTES BF LOCALITIES dry brick-machine, three turning-wheels, two grinding-and-tempering-machines, clay-washing apparatus and compressor, two tall updraft kilns (for sewer-pipe, flues and some grades of pottery) and four circular and one rectangular down-draft kilns. The clay, used, consists of a mixture, according to the product desired. In part, Ocmulgee alluvium from Macon is employed; and in part, red clay from the Lafayette beds on neighboring hilltops; and, further, the white fire-clay, probably Potomac, which is obtained at a number of different points on the extensive lands of this company; but chiefly, that found along the line of the railroad, for a mile or more from the works. About three quarters of a mile west of the railroad, on the slope of a low hill, a large pit has been opened, where fire-clay is found, near the surface, and covered with but little stripping. The clay is white, as a whole; but it contains more or less iron, and is stained in places a deep red. The Lafayette gravels overlie the clay, resting unconformably on its very irregular surface. The average thickness of the latter is fourteen feet. It is somewhat sandy and micaceous. Underlying it, there is a stratum of white sand, three feet in thickness. Beneath this, in turn, is another bed of fireclay, the thickness of which could not be determined. An average sample of the best grade of fire-clay from this locality is very fine-grained and pale buff in color. Under the hand lens, a few scales of muscovite may be seen; but they are not abundant. Under the microscope, with the highest power, only an occasional grain of quartz can be detected; and there are no quartz grains, over .oo 5 of an inch in diameter. A chemical analysis gave the following results:- NOTES BY LOCALITiES I39 Hygroscopic Moisture Loss on Ignition-Combined Water, C02 Etc. 13.64 Combined Silica . . 43.85 Free Silica, or Sand . 2.77 Aluminum 38.28 Ferric Oxide . r. 02 Lime .. 0.18 Magnesia 0.00 Potash o.os Soda . o.o8 Total Clay Base. Fluxing Impurities 9577 !.33 This clay absorbs roo per cent. of its weight of water. It has a linear shrinkage of 8 per cent., and an additional shrinkage, on burning, of 2 per cent. Its specific gravity varies from r.6g to r.7 5; while its tensile strength is 24 pounds per square inch. It burns to a fine pinkish color, and gives a moderately firm brick. It does not crackle, if burned carefully. Its fusing point is about that of Seger cone 3 5. The Lafayette, at this point, contains, in places, a clay, some of which is used, in the manufacture of brick and sewer-pipe. It has a rusty color; is porous and sandy; and contains grains of quartz, ranging up to one-sixth of an inch in diameter; also, fragments of feldspar, which have been altered to clay, since their deposition. Fully 50 per cent. of the mass consists of quartz. It seems to have been an original sandy layer, made up of quartz and feldspar, and the feldspar has in time decomposed, and furnished the clay portions, in situ. It is all permeated with yellow iron oxide, and it contains some large grains of magnetite. South of .the works and adjacent to the railroad track, there are 140 XOTLS l!l- LOCUIT!ES several pits, or quarries, where a variety of clays may be seen. These occur at intervals, the farthest being a mile, or more, away. At many of these Localities, the clay occurs at approximately the same level. At intermediate points, however, it is cut out and replaced by orange sands of the Lafayette formation. At the first of the clay pits, going south along the railroad track, there is evidence of two unconformities. The section exposed, here, in descending series is as follows:- Orange sand, containing clay in some places, and in others, coarse, water-worn pebbles. It is often indurated, and much stained with Iron - __ - ___ __ ____ _ ____ __ ____ __ __ 3 to 8 feet C n co nfornz ity. 2 \Vhite sand, which contains much kaolin re- sulting, in part, at least, from the decomposition of fragments of feldspar. It is indurated in places, and is often cut out by the overly- ing orange sands, as is also the underlying clay, which, in turn, is partly unconformably replaced _____ . __ _ __ _ _________ _ ______ __ o to 6 feet Unconformity. 3 \Vhite and gray clay, which contains some sand, and is much jointed, but not so much so, as that, seen in other localities in this vicinity. It contains considerable iron oxide near the upper surface _________________________ 3 to 6 feet 4 Cross-bedded sand, iron-stained, and both fine and coarse. It contains many thin seams of limonite, which often lie in the plains of the cross-bedding ____________________________ (?) Resting on the irregular surface of the clay, number 3 of the section, are some interesting pebbles and boulders of clay,' some 1 See Plates VII and Vl!I. 141 of which are several feet in diameter. They arc partly, and sometimes wbolly, surrounded (except at the contact surface with the white clay beneath) by an orange sand. These balls are irregular in shape, and as variable in size. They arc apparently made up of small fragments of clay, water-worn, but not disintegrated, which have been re-cemented by clay. The color contrasts are sharp and the fragments stand out from the matrix beautifully. The origin of these clay-conglomerates, as they might be called, is as hard to explain, as is their present position. The writer has seen a clay breccia, where a hard flint-clay seems to have been crushed and resolidified by infiltrating clay, deposited by water; but, in the case at hand, there is too little angularity in the fragments, to suggest, that these masses, have been formed in this way, in their present position. They seem certainly to have been brought or rolled there, by currents, which cut out more or less of the clay-bed, already deposited, and which, later, deposited the surrounding materials. They arc certainly younger than the clay stratum, and older than the gravels; for a stream, that could deposit such masses, would hardly deposit sands and clay. In Plate VII, the unconformity is plainly seen, being pointed at, by the boys standing. along the face of the exposure. In Plate VIII, a cross-section of the fragments of one of these boulders, three feet in diameter, is illustrated. At the second pit, going south, a quarter of a mile, along the railroad track, still other interesting phenomena may be seen. The nature of the surface drift of orange sand changes, here, somewhat. It contains more clay and less sand; but it is remarkable for a considerable percentage of fragments of clayey shales, which it contains, a shale resembling that described, as occurring on the Gordon road, between Lewiston and Gordon, south of the Southern Rail- I 42 XOTES !JY LOCUJT!ES way track. In addition to these masses of shale, it contains very many irregular fragments of a white clay, evidently belonging to the older beds, lying beneath it, in the section, which is additional proof, if that were necessary, of the unconformity existing here. The white sand, found at the first pit, is wanting at the second; and, in its place, are beautiful orange sands and a bed of two varieties of clay, curiously mixed. It is difficult to understand the relation of these two clays to each other. The one is hard and white, rubbing into a soft, flourlike material, between the fingers. It is very much broken up, and the surfaces arc universally slic kcnsided and stained with oxides of manganese and iron. Included in, or associated with, this white clay, in the same bed, are irregularly shaped masses, some a yard in diameter, of a different kind of clay, the general color of which, at a distance, is bluish. On close inspection, it appears mottled, as though some segregating action had taken place. It is quite hard, and absolutely free from grit. It cuts, with a knife, with extreme smoothness; and it is so tough, that thin, curling shavings, of considerable length, can be whittled off. It is waxy, in nature, but a little harder than wax, and submits to carving, perfectly. It would seem, therefore, to be perfectly homogeneous. Some of these masses arc, however, coarser and more porous in nature. In general, on weathering, this variety breaks up, somewhat concentrically, so that, on the surface of the bed, the fragments arc as small as an acorn, or smaller. As the result of this tendency, these pockets, or the masses of this particular clay, fall out from the face of the pit, faster than the white clays, surrounding them; so that they leave cavities, in the face of the latter, which is present in much the greater amount. The phenomenon, here, is the exact opposite of that in the case XOTES I!}. LOCdLJ71ES 143 of the clays, which have a nodular appearance, and which occur south of here, as described on the l\Iiller estate, and elsewhere. In the latter case, these peculiar masses, which are, however, very different in nature, become indurated on weathering, and project above the surface. It is difficult, at present, to account for these phenomena. It might be suggested, that the blue clay had been washed into cavities of the white, made by springs or streams of water; but it should be noted, that the white clay next to the blue clay, which is completely surrounded, is thoroughly jointed and slickensided by compressive forces. The blue clay, however, does not penetrate these cracks. It is evident, therefore, that the crushing and slickensiding of the white clay must have been later, with regard to this hypothesis, than the infiltration of the blue variety, the blue being harder, and \\"ithstancling the crushing, which broke up the white. There are veins of the white clay, which cut across the blue masses; and this would seem to indicate, that the white clay is the younger of the two; but it is impossible to conceive, how waters, free from masses of ice, could deposit large boulders of the hard, compact clay, while it was depositing, grain by grain, the minute particles, which constitute the white clay. It is possible, of course, that the veins of white clay are secondary and comparatively recent, being subsequent to both the blue and white varieties. Near the bottom of the white clay, there seems to be a more intimate mixture of the two kinds. If these widely different clays are, then, phases of one original sedimentary bed, how can we account for the great difference in character, and, especially, that one is wholly free from grit: Different stages of induration, or the presence of varying amounts of impurities, or infiltrated mineral deposits, might easily be imagined, as occurring in different places in I44 XOTES BY LOCUJT/ES the same bed. Physical segregation, or flocculation, could be conceived, as bringing about striking differences in the character of such deposits in different parts of the bed. But it cannot be seen, how the phenomena here could be thus explained. An additional matter of interest, in connection with these phenomena, is the presence, in the blue clay, of thin veins, which ramify through the boulder-like mass, but which do not penetrate the white clay, and arc older than the veins of white clay, above referred to. These veins consist of what seems to be a new mineral, judging by a preliminary analysis. It is a transparent hydro-silicate of aluminum, having a yellowish color and a soft, waxy consistency. Beneath this blue-and-white clay bed, comes in the white clay, or "chalk," where it lies at a considerably lower elevation, than at the other pits. It is highly micaceous, and is used for fire-brick and for pottery, when properly mixed with other clays. The section, here, is as follows : - Orange sands, very clayey and full of fragments of shale and "chalk" ____ _ __ _ I 2 to I 5 feet 2 Blue-and-whiteclaybeds _____________ 8 3 white micaceous fire-clay _________________ 3+" A hand specimen of the fire-clay, from bed No. 3 of this section, shows a friable, white to pale-yellow clay, containing a large amount of muscovite and some small crystals of magnetite. Under the microscope, many basal sections of muscovite and magnetite, along with a few crystals of calcite, which show the planes of the rhombohedron, and are about .oo I of an inch in diameter, are observable. There are also present many prismatic sections of muscovite crystals; while quartz grains are wholly absent, even those, with a diameter as small as .0002 of an inch, being rare. This clay has a specific gravity, varying from r.7o to r.So. It .., :::: 1'1 '."..). :,_ ~ Cl ": .t.',l > ";";"': r r 0 r NOTES BY LOCALITIES 145 shrinks, on drying, about 6 per cent.; but, on burning, no additional shrinkage is observable. It has a tensile strength, dried, of 24 pounds per square inch. It burns, with little crackling, to a white, and sometimes faint pinkish, color. SUl\Il\1IT About six miles northwest of Griswoldville, and north of the Fall Line, is an outlier of Tertiary strata, unlike any of those seen at other points in the State. They are exposed in the railroad cut, at a point known as "Summit," where they reach an elevation of 2 50 feet above the Macon bridge. These beds are limited in extent, and are surrounded by decomposed schists and diabase dikes, belonging to the Piedmont Plateau. On the eastern extension of this railroad cut, they may be seen to lie directly upon the decomposed schist, which is here cut by a dike of the fine-grained diabase rock, thirty feet in thickness. This outlier consists of bluish and greenish, more or less laminated clay, which, in several horizons, is densely packed with shells and shell fragments. About thirty feet of clay is exposed in the railroad section; and it is capped by gravel beds of the omnipresent Lafayette. An average sample of fossil-free material was collected and analyzed, with the following results:- ;'\'OTES BY LOCAIJTIES Analysis of an average sample of workable clay, collected at Summit, near Roberts station, Jones county. Hygroscopic Moisture Loss on Ignition, Combined Water, C02 Etc. I9.4I Combined Silica . . I 3 62 Free Silica, or Sand 36.8o ~\lumina I I. 56 Ferric Oxide . 2. 20 Lime .. I3.89 :\Iagnesia Potash I. 73 trace Soda . 1.36 Total I00.57 Clay Base Fluxing Impurities 4459 I9. I 8 Hand specimens, taken from this bed, show a slate-colored massive and tough clay, more or less filled with remains of gastropods. It contains, also, a few visible scales of muscovite; and it has a coarse, gritty feel. Under the microscope, an abundance of small black specks, of what seems to be carbonaceous matter, possibly mixed with magnetite, is apparent. These vary in diameter, from .o I of an inch to .002 of an inch. Quartz grains, which range, in size, up to .007 of an inch in diameter, are seen to be present. Samples, taken from the top and bottom of this bed, respectively, show, under examination, almost identically the same characteristics, as appeared in the test of the above described sample. This clay, when dry, absorbs g8 per cent. of its weight of water; and the dried, powdered clay, instead of shrinking and settling in the vessel, as it absorbs water through the perforated bottom,, ,\'07l:S lJ l. D!C.i!ITJES swells- in some cases, projecting an eighth of an inch, or n1ore, above the top of the vessel. It shrinks, on drying, I 8 to 20 per cent., and, on burning, an additional 2 per cent., or even less. The tensile strength of an airdried briquette gave results, varying as follows:- Sample from base of beds, I 43 pounds per square inch. 2 Sample from middle of beds, 304 pounds per square inch. 3 Sample from top of beds, 2) j pounds per square inch. The specific gravity varies from I .So to 2.00. Owing to the large amount of lime present, the fusing point of these clays is unusually low. The most refractory sample completely melted, at a temperature of I ,280 C. An average sample fused at I, I 00. \\'hen burned, at a moderate heat, the product is a substantial, pale-buff-colored brick, without cracks or Haws. This clay would make an excellent material, to mix \\ith the white l'otomac cla\s or the alluvial clays of l\Iacon, for the manufacture of vitrified paving-brick. .\IILLEDGEYILLE :-Iilledgeville is situated just above the Fall Line, on the red hills, capped \\ith the soils of the decomposed Piedmont crystallines; and it overlook,; the Oconee ri\er from the western side. The sedimentary rocks begin to disappear, about six miles south of :\Iilledgeville, \\here the decomposed, upturned, micaceous schists, with their numerous quartz veins, begin to appear. For some distance north of here, however, the latter are still capped, in places, with 148 NOTES BY LOCALITiES layers of drift. In many places, the soil has lost its red color, especially near the surface, and becomes a gray or "mulatto," the change being due, apparently, to the solution of the iron stain by organic acids. The prevailing reds, in the gneiss and schist regions, are probably due to the presence of iron-bearing minerals, which furnish a constant supply, through their decomposition, of the iron, which is oxidized and stains the soil. In the city of Milledgeville, there IS but one industry, utilizing clays, namely, The Milledgeville Brick and Pottery \Yorks, the property of Mr. J. \V. McMillan. These are the only clay-works in Baldwin county, except those at Stevens' Pottery. They are situated on the second river-bottom of the Oconee, near the footbridge, which crosses that river. The clay, which is worked here, is doubtless of Columbia age. It is a plastic alluvium, which varies in character, as all alluvial clays do; but it is workable, at this point, to a depth of ten feet from the surface. \Vith the clay, obtained locally, is mixed, to some extent, for the manufacture of bricks, the white, micaceous Potomac clay, obtained at Carr's station, in Hancock county, where it occurs in a cut on the Georgia Railroad. The clays arc mixed, according to the desired texture and color of the burned product. The product consists of common building-brick, re-pressed faceand ornamental-brick, and, also, tiles and a variety of pottery, such as garden urns, fancy vases, and large jugs and flower-pots, the latter being of exceptional high-grade. About 2,000 bricks per day are made. The plant, as illustrated on Plate XII, consists of an office, store-house, drying-house, Penfield brick-machine, hand re-press-machine, turning wheels, flower-pot machine, with a capacity of 3,500 per day, five rectangular brick-kilns, one circular, up-draft pottery-kiln, divided into vertical compartments, one rec- 11-0TES BY LOCALITIES I49 tangular, down-draft pottery-kiln, one steam-engine and boilers, and a tram and tram-cars. The works were established in I 88 7; and the product is shipped all over the South, even to points in Texas. \Vood is used in burning; but, at the time of the writer's visit, it was the intention of the proprietor to use coal, and put in new and improved machinery. THE RECIO~ WEST OF MILLEDGEVILLE \Vest of Milledgeville, along the Fall Line towards Macon, the character of the crystalline rocks varies rapidly; and they pass from coarse gneisses, resembling granite, but with a true gneissic, banded structure, to laminated schists, the planes of schistosity being folded, clipping downward, here and there, and giving the rocks the appearance of standing on edge. They are decomposed, to a depth of from I 5 to 20 feet, but not completely so; as there are, usually, in a decomposed mass, cores of solid rock. The color of the soil varies, as already stated, from red to gray; and there is often a sudden transition in color, corresponding to the kind of crystalline rock below. Among the sedimentary formations south of the Fall Line, there are also reel and gray soils, sharply separated from each other, in just the same way; though the sudden transition in this case is the result of a different cause. KOT/o'S JJJ' J:OCAL/T/ES THE AuGUSTA REGION AND EASTERN EXTENSIOX OF THE FALL LI~E CLAYS OF GEORGIA East of Baldwin county, the Fall Line, as stated on preceding pages, crosses and re-crosses the Georgia Railroad, on the whole averaging south of it. The white Potomac clay occurs, as described in the l\Iilledgeville notes, at, or near, Carr's station on the Georgia Railroad, in Hancock county, and at other points, on this road, near "\ugusta. South of here, its occurrence becomes rare, until it finally disappears, as usual, beneath the Tertiary strata. It may be found, at intervals, along the lines of the Augusta Southern Railroad, between Sandersville and Augusta, and crossing parts of \\'ashington, Glascock, Jefferson and Richmond counties. THE \\'ORTHEN LOCALITY The most important exposures, along the line of the Augusta Southern Railway, are near Chalker and \Vorthen, in \Vashington county. It occurs, in large quantities, at Magnolia Plains on Floyd's creek, and at the \Vorthen and Upper Mills on Keg creek. At the first of these three places, it is pure white, and contains but little grit. At the other, it is coarser and more siliceous. \Vashington county, in which these occurrences are situated, has a number of small potteries, operated in a manner, similar to those in Crawford county. The wares are made, at intervals during the year, and are disposed of, by peddling through the country. KOTES Bl' LOCALITIES The leading potteries are those of ]. M. Bussell, John Redfern and Andrew Redfern. The business has been carried on, for the past 75 years, or more. At Chalker, the white clay, which seems to be Potomac, is exposed in the railroad cut, and has a very irregular surface, showing a maximum thickness of twelve feet, and being unconformably overlaid by the following series of Tertiary and Lafayette material:- Lafayette, sandy loam, } feet covering the slope ----I 5 to 20 2 Coarse, micaceous, laminated clay, varying in color from drab to yellow, weathered into small cubical and angular fragments _______ G 3 Fossiliferous, sandy clay, indurated and siliceous in places ______ __ __ _ _____ _ _ ____ 4 to 6 4 Hard, siliceous layers, undermined by the stream in the immediate vicinity, where beds are exposed thirty feet in thickness and resembling a quartzite. It contains many fos- sils _______________________________ I to 2_Yz" 5 Dark-drab and brown, iron-stained, sandy clay __ __ __ _ _ ____ _ __ _ ____ ___ _____ ________ 8 THE AUGUSTA CLAYS The geological conditions, seen at Augusta, which is situated at the head of navigation on the Savannah river, are very much like those at l\Iacon and Columbus, more especial!y Macon, where the Potomac formation is not observable in the immediate vicinity of the city. NOTES BY LOCALITIES \Nest of the city, however, and at a considerable elevation above it, in Richmond and Columbia counties, are exposures of what is doubtless the white Potomac clay. In this region, there are, also, observable numerous sections of Tertiary strata; abundant sections of the Lafayette, resting unconformably on the strata beneath it; and frequent sections of the decomposed crystallines, showing the unconformable contact between them and the overlying sediments, which contain, at their base, numerous fragments of the crystalline rocks, and immense quantities of muscovite and other minerals derived from it. THE CLAY INDUSTRY OF AUGUSTA The clay industry of Augusta is confined chiefly to the manufacture of building-brick, although a small amount of tiles, ornamental ware and terra-cotta is produced. A part of the industry, really belonging to this community, is across the river, in South Carolina. The clay, used, is Columbia alluvium, occurring in the plains, on which the business portion of Augusta stands. The maximum production on both sides of the river, in any one year, has been 30,ooo,ooo bricks; while the average annual production is about 20,000,000. THE AUGUSTA BRICK CO:\IPA:::-fY This company is said to have the largest brick-yard m Georgia. It was established by a man named DeLaigo, a refugee from the San Domingo massacre. The product consists of common and THE CLAYS OF GEORGI A PLATE XVI GENERAL VI EW OF THE FALL L INE, OPPOS ITE COLU~ I BU S, GEORG IA, S H OW ING RECENT EROS ION. THE UPTURNED CRYSTALLINE ROCKS ARE OVER LAID BY C RETA CEOUS AND CO L U~ I B I A FOR~ I AT I ONS. ( Fo r D etail Vi ew, See Plate XVII .) NOTES BY LOC/1LITIES 1 53 ornamental brick (hand pressed). The average annual production is said to be about 14,ooo,ooo, most of which is common brick. The bricks are made by 3 Sword machines (stiff clay process), having a capacity of Io,ooo per day. They are burned, in four ordinary clamp kilns. Wood, at the average cost of $3.00 per cord, is used in preference to coal, for burning. The plant is situated on the southeastern edge of Augusta, on the flood-plain, and about 30 feet above the surface of the river. The clay used is excellent in quality, and free from any excess of sand and mica. A sample of alluvial clay, a fair average of that used by the various companies, was collected for physical examination, the results of which were as follows: - Its specific gravity is approximately 2.00. It shrinks, on drying, 8 per cent., linear measurement. Its tensile strength, dried, is 148 pounds per square inch. It burns to a fine, strong, red brick; but, owing to the impurities present, it is, of course, not a refractory or fire brick. It fuses, at a little less than 1,300 C. THE WILBUR BOSWELL PLA~T Mr. Boswell produces, annually, with a Sword machine and four or five clamp kilns, a large number of common- and a few facebrick. His plant has a capacity of Jo,ooo per day. THE McCOY BRICK AND TILE COMPANY This company has an elaborately equipped and thoroughly modern brick-yard. The plant consists, in part, of one continuous kiln, of the Youngrens pattern, with a capacity of 30,000 per day of twenty-four hours; one Swift kiln, changed from an original Morrison, with a capacity of soo,ooo; one Phillips dryer (with ten 154 1\'0TFS BJ' J:OCAIJTILS racks), heated by exhaust steam from the engme, which is run through 16o,ooo feet of pipe, the air, thus heated, being agitated by 26 fans. The bricks are dried, in the last named apparatus, in about 24 hours. They arc introduced and removed, on cars. It has a capacity of 20,000 per clay of ten hours. There are also open-dryers, consisting of covered racks, which carry I 20,000 bricks, and are capable of turning out 20,000 per day. The system of operating, at these works, is interesting. The clay is brought from the dump, in cars holding a little less than a cubic foot each. These are elevated, on cables, by a winding-drum, and are emptied into an immense granulator, which crushes and mixes the clay with sand. This granulator delivers the clay, at an angle of 45, into a machine, which is crusher, pug-mill and auger brick-machine combined, and which delivers, upon an apron, side-cut brick, with the "flats," rough, and the exposed edges, smooth. The machine is made by E. l\I. Freese & Co., of Galion, Ohio. It has a guaranteed capacity of 40,000 per clay, and can be made to produce 6,000 per hour. The company has, also, a I oo horse-power engine, with I I o horse-power boilers, and a 55,ooo-gallon water-tank, elevated on a 72-foot tower. The yard is equipped for re-press work; but, with the brick-machine, now used, this process is not necessary. The clay is obtained from the river bottom, about Ys of a mile from the works, to which it is drawn, on a tram, by mules. KO TFS B V LOCALITIES I 5J THE GRO\'ETO\\'~ DISTRICT Gro\etown is about 20 miles west of Augusta, on the Georgia Railroad, near the southeastern boundary of C5Jl umbia county. Here, as also in Berzclia on the west, Belair on the east, and the adjacent territory in Richmond county on the south, there occurs a great abundance of clays of many varieties. The white clay, ol" "chalk," has been shipped from a number of points in this region, for a variety of uses. The only developments of clay, in these two counties, except that of the industries, already described in Augusta, is that of a small pottery at Grovetown, where, convenient to the railroad and an excellent bed of clay, a high grade of common pottery is produced. In a railroad cut, just east of Grovetown station, there is an exposure, for a considerable distance, of the upper part of a bed of clay, only three feet of which can be seen, which is remarkable in character. \Vhen fresh from the bed, it is from gray to buff in color; but it is sometimes stained with yellow and reddish tints. It seems to be wholly free from grit, and is carved readily with a knife; but it will not disintegrate in water, although it can be crumbled with the fingers; and, when ground up, it becomes exceedingly plastic. It is a soft clay; but it breaks, on weathering, concentrically. Although soft, neither rains, nor the waters, which constantly seep through its joint-planes, and flow down into the railroad ditch, make any appreciable impression on the bed, as regards the removal of material. In spite of its seemingly favorable properties, it cannot be used, at least without the addition of other clays, in the manufacture of burned products, owing to its tendency to pop and fly to pieces, NOTES BY LOCALITIES with explosive violence, on being heated, regardless of the care, with which this is done. The cause of this has not yet been investigated. Fossils are said to have been found in this bed; but none were seen by the writer. It may be of Cretaceous age; but it is probably Tertiary. A hand specimen of this clay may be described as being from buff to gray in color, with yellow iron-oxide stains, along the joints. It is compact and very fine-grained, and has a conchoidal fracture. Under the pocket lens, it shows traces of mica, but no quartz. Under the microscope, with a high power, minute scales of muscovite appear in great abundance; also quartz grains, ranging up to .oo I of an inch in diamerer, and an occasional minute crystal of magnetite. The specific gravity of this clay is found to be very uniform throughout the bed. The determination of many samples gave 1.30 as aresult, with no appreciable variation. It shrinks, on drying, about I 6 per cent., and, on burning, an additional 4 per cent. It is one of the lightest clays examined. The tensile strength of dried briquettes is 144 pounds per square inch. It burns to a buff color; but, however carefully burned, it bursts into many fragments, at a comparatively low temperature. It is overlaid, with a bed of Lafayette red clayey gravel, which would make an excellent road material, and might be profitably used for that purpose in Augusta. SILAS REED'S ESTATE On the property of Mr. Silas Reed, near Grovetown, a small stream, resulting from springs, has caused a "break," a quarter of a mile in length, along the hillside. The water moves on the surface of a bed of dark-colored, tough clay, known in this locality, as NOTES BY LOCALITIES I 57 "umber," and once worked for a paint material. It 1s simply a clay, which contains a large amount of carbonaceous material, in places becoming so far lignitic in character, that it will burn, although with difficulty. Sometimes the clay resembles that, described as occurring in the railroad cut at Grovetown; and, also, the exceedingly light variety found at Fitzpatrick. Dr. Hatton, of Grovetown, stated to the writer, that fossils have been found in this horizon, where it has been penetrated by wells. This bed of lignite and clay is exposed to a depth of from I 5 to I 8 feet. Its color varies from cream to brown and black. A deep shaft was sunk here, by prospectors in search of umber; but a record of the beds passed through could not be obtained. This clay does not absorb water, at least until crushed and powdered. Under the microscope, small amounts of muscovite, occasional grains of quartz, and large quantities of organic matter are visible. Overlying it, is an enormous mass of red, deep-orange, and goldenyellow sands, with, here and there, a seam of clay, evidently of Tertiary age. THE MARY INGLETT PROPERTY This property is about three miles south of the Georgia Railroad, near Grovetown. There is here, in a gully, on the edge of a sandy plateau, an exposure of white clay, known locally by the usual name, "chalk." It is almost wholly buried, and hard to examine. Its thickness could not be ascertained. The clay and conditions in general suggest strongly the occurrence on the VanBuren estate in Jones county, as described above. The clay bed is overlaid by a sand, mostly quite coarse, and consisting of fragments of white and smoky quartz, and containing partings and occasional isolated NOTES BY LOCAIJTIES masses of clay, derived from the bed beneath. The surface of the country, about, is covered with just such sand, the smaller grains of which are sharp and angular, while the larger are well rounded. This formation is many colored; contains, throughout, seams of clay; and is doubtless Lafayette. On the extreme surface, many of the quartz pebbles have been carved by wind-blown sand to a remarkable extent. Among these, have been found good imitations of octahedrons; and those, showing pyramids on one side, are of frequent occurrence. The clay itself is not all white; but it is occasionally pink and mottled. The pocket lens reveals an abundance of quartz grains and many scales of mica. Some of the quartz is smoky. There may also be detected many distinct cleavage fragments of partially kaolinized feldspar. Under the microscope, the quartz grains appear in great abundance, and many scales and prisms of muscovite are visible. There may, also, be seen a few remarkably shaped bodies, the dimensions of which vary from .o I to .02 of an inch. They are probably organic, and most likely, the remains of diatoms. Prisms of zircon, also, occur. The clay has a specific gravity, varying from r.S to r.g. It shrinks, on drying, 8 per cent., linear measurement, and an additional 2 per cent., on burning. It has a tensile strength, dried, of 20 pounds per square inch. It burns to a pinkish or cream color. Its fusing point corresponds to that of Seger cone 30; and it is therefore highly refractory. BELAIR There is an excellent opportunity at this place, to study the relations between the decomposed crystalline rocks and the overly- KOTES JJ Y LOCALITIES 159 ing sediments, which are so largely derived from them. It is well illustrated by a section in the railroad cut, just east of the station. The exposure, here, is about 20 feet in height. The fissile structure of the decomposed schists, at the base of the section, is very pronounced; although the decomposition of the rock, as a whole, is almost complete; and the resulting material is, at least in many places, homogeneous, fine-grained and plastic. It is beautifully vari-colored,- chocolate, red, golden-yellow, white and gray being the predominating colors. In some localities, this rock seems to have been a fine-grained chloritic schist; but, in other places, it resembles shale. The dip of the schistose planes varies from 45 to 60. This crystalline rock is cut by prominent quartz veins, which, although broken, have remained hard and unaltered, while the rock about it is decomposed. The quartz veins project above the irregular surface of the crystallines, showing, that, during the process of erosion, which went on, when this was a land surface, the surrounding rock was worn away, further than the quartz veins. Another feature, which tells the same geological story, is the distribution, at the contact of the sediments with the upturned crystallines, or along the whole irregular surface of the latter, of large irregular-shaped boulders of quartz, which are evidently residuary from quartz veins, once resting in the crystalline rocks, but which were left behind, as surface boulders, while the bed-rock itself was decomposed and removed. About these, but of course unconformably resting on the crystallines, is a bed of coarse angular sand and gravel. Since the clays, which have been studied, have been largely de- rived, with their impurities, from the decomposed crystallines, a sample of the latter, from this place (where, although it has not been removed and sorted out by the running water, it is neverthe- r6o NOTES BY LOCALITIES less thoroughly decomposed), was selected and submitted to physical tests, similar to those employed in the case of clays. The results of a physical examination of this material were as follows:- A hand specimen shows a massive mixture of kaolinite, muscovite, quartz and feldspar, and also numerous bright crystals of magnetite. It is, therefore, seen to contain exactly the same minerals, that are found in all the clays examined along the Fall Line, except that the latter consists more completely of the finergrained material, kaolin, the coarse particles, quartz, magnetite, feldspar and muscovite having been removed by the differential carrying capacity of moving water. Under the microscope, with a low power, a large amount of sericite, in minute crystal plates, and occasional crystals of calcite are seen. The specific gravity of this material varies from 2.03 to z.og. It shrinks, on drying, 4 per cent., linear measurement; but, on burning, there is no additional shrinkage. The tensile strength of the dried mass is very low, being not over five or six pounds per square inch; and the dried mass crumbles readily between the fingers. It burns to a porous, friable substance, and would make good brick material, with the addition of a little plastic clay. It is not refractory, but fuses completely, at a comparatively low temperature. H. F. CAMPFIELD'S PROPERTY A section, somewhat similar to this one at Belair, may be seen on the property of Mr. H. F. Campfield, about three quarters of a mile east of Lula station, on the Knoxville road. About ten yards northwest of the exposure in the railroad cut at Belair, there is an occurrence of sand and gravel, sometimes white, but often red and yellow, and containing occasional thin seams of TI-lE CL A rs OF GEO RGI A PLA TE XVII VIEW OP POS IT E COLU~ I IlUS, GEO RG IA, S HOWING TH E UPTU RNED C RVSTALLIN E ROCKS OF TH E PI E DM ONT PLATEAU, OVERLAID BV C RETA CEOUS AND COLU MBIA FO RMATI ONS. ( For a Generol View of thi s Locality, See Pbte XVI. ) . NOTES BY LOCALITIES I6r limonite; while, here and there, it is cemented into a solid conglomerate by iron oxide. Contained in these gravels are, also, irregularshaped pockets, sometimes several feet in thickness, of fire-clay, which dries white, although it is frequently colored with iron-oxide stains. It is fine-grained. Beds of fire-clay, similar to those occurring in the gravels at this locality, are found at other points in this region, notably at a point on the railroad, near the I 2-mile post (between Belair and Grove- town), and, also, at a point 2Yz miles south of Belair, where there is a bed of it, excellent in quality. Partially buried beneath this gravel, which may be either Ter- tiary or Lafayette, is a comparatively hard rock, which seems to be a partially decomposed gneiss. The structural planes are, however, horizontal; and it may consist of slightly re-arranged arkose, derived from gneisses, which contain an abundance of quartz and fe,ldspar crystals, the latter, in this case, being thoroughly kaolinized and consequently soft. Such beds as this need be observed critically, to distinguish them from many of the sedimentary gravels, which overlie them. A hand specimen of the decomposed gneiss, shows a white to gray, porous-looking material, stratified or laminated, and very friable. It is gritty and possesses little plasticity. In a strong light, it glitters, with a white, satin-like luster, caused by an immense number of minute scales of some micaceous mineral. Under the microscope, grains of quartz are visible, ranging up to .o I of an inch in diameter. Fully 50 per cent. of the mass is seen to consist of prisms and plates of a pale-straw-colored mica, the plates rang- ing up to .003 + of an inch, in diameter. These plates, or scales, appear to be muscovite, and the prismatic sections give very high interference colors. It might be classified as sericite. The material contains also a little magnetite and masses of kaolinite scales. 162 1\'0TES BY LOCALITIES DEPOSITS EAST OF BELAIR, ALONG THE GEORGIA RAILROAD East of Belair, at the eight-mile post, on the Georgia Railroad, are thick and massive beds of clay, sand and gravel, the clay, or kaolin, being often intimately mixed with the gravel, in a manner hard to explain, as it would seem, that water, depositing such coarse sand and gravel, which is often cross-bedded, thus showing the presence of strong and varying currents, would entirely wash away the fine-grained clay. On both sides of the cut, striking unconformities are observable. An illustration of the better of these is shown in Plate V. The irregular surface of the lower-lying series seems to have been carved beneath flowing waters, which, subsequently, under changed conditions, deposited the overburden. The contours of the surface of the former are too sharp and irregular, to have been developed on a land surface. There is probably represented, here, a deposit of Lafayette on the Lower Cretaceous mixture of sand and gravels, the former consisting of materials derived from the latter, which is apparently a continuation of the sands occurring in Jones, Baldwin and other counties, under similar conditions. In the high slope, above this exposure, are coarse beds of residuary gravel, lying on the extreme surface. They are mostly composed of smooth, well-rounded pebbles. The fields, too, are often covered, after a heavy rain, with very coarse, white and transparent c1uartz sands, which produce a glittering effect like that of snow. NOTES BY LOCALITIES NINETEEN-MILE POST, GEORGIA RAILROAD RICHMOND COUNTY At this locality, there is a clay, almost white in color, which is very plastic, and contains isolated grains of c1uartz, scattered through the mass. It has been crushed, and again cemented together, by the infiltration of a finer clay. The upper layer of the bed, two feet in thickness, is full of areas of clay, with the peculiar nodular effect, characteristic of the variety found on the Miller estate, which has been described above. These areas are somewhat indurated, as in the case of the Miller clay; and, where the bed has been weathered, they project beyond the surface. Unconformably overlying this clay, is a bed of grayish and yellow, very hard, but rather porous, clay, containing sand, in patches and isolated particles, in all, I 5 to I 8 feet in thickness. It is vari-colored, being gray, yellow and pink in different places, and frequently mottled.. The quartz grains, contained in it, are rounded. It contains the same filled cavities, or nodules (?), as in the bed below. Overlying it, are massive beds of incoherent bands, which, however, in places, are strongly crossbedded and full of water-worn pebbles, some of which are rounded fragments of limonite. These sands carry, also, much clay, scattered through them, and as numerous vari-colored partings. A hand specimen from the lower bed shows grains of quartz, some of which are as much as a sixteenth of an inch in diameter. Under the microscope, grains of magnetite are visible, and some quartz, although small grains of this mineral are rare, the larger ones being such as could be easily removed by washing. Muscovite is in abundance, there being only an occasional prism, but what is over .oo I of an inch in length. The kaolin is in aggregates, which do not NOTES BY LOCALITIES readily disintegrate. Zircon needles are observable, averaging .003 of an inch in diameter. The little aggregates of kaolin vary in size from .oor of an inch to .0002 in diameter; and they are usually stained a pale-brown color. A hand specimen, selected from t!ze upper bed, is of a beautiful pink color, with numerous parallel partings, varying in color, and showing a thin seam of iron oxide deposited along the planes of separation. Considerable mica can be recognized with a pocket lens. The study of this clay, under the microscope, reveals a considerable amount of foreign matter, consisting mostly of angular quartz grains, the largest of which are .ooo6 of an inch in diameter. With a high power, the double-refracting clay particles are numerous; but nearly all are so small, that their thickness is insufficient to produce an interference color of the first order. The finest material is often stained a pale-yellow color. Muscovite is present, in basal sections, in prisms up to .ooo8 of an inch in diameter. The specific gravity of this clay varies from 1.53 to 1.76. It shrinks, on drying, about ro per cent., linear measurement, and an additional 5 per cent., on burning. Its tensile strength, dried, is 2 5 pounds per square inch. It assumes a pink to reddish color, on burning, and makes a porous, friable brick, when burned without admixture of other clay. THE SE\-ENTEEN-MILE POST, GEORGIA RAILROAD COLUMBIA COUNTY At the 17-mile post, there occurs a white to yellow friable clay, with comparatively little grit, and free from impurities of any kind .. NOTES BY LOCALITIES It resembles the best clay, seen in Jones and adjacent counties. Its specific gravity is 1.70. It shrinks, on drying, 8 per cent., and a small additional per cent., on burning. Its tensile strength, dried, is 2 5 pounds per square inch. It is highly refractory, and has a fusing point between that of Seger cones 35 and 36, and is, therefore, one of the best fire-clays, as regards refractoriness, which has been examined. ALONG THE GEORGIA RAILROAD, WEST OF GROVETOWN Traveling westward on the Georgia Railroad from Grovetown, days are observed in cuts, much like those already described, in this vicinity, being colored red, white and yellow. They are seen, also, near Boneville, just east of the station, and, again, some little distance west of it. The layer of sediments near Boneville, becomes very thin, and the underlying schists are exposed, in all the stream-beds. Near Thomson, granitic rocks occur; and, from Thomson to Camack, the nystalline rocks alone are exposed. CHAPTER IV A COMPARISON BETWEEN A GEORGIA CLAY AND OTHER WELL-KNOWN CLAYS OF THE UNITED STATES The localities of a series of widely-known clays, which the writer has selected, and which are here placed in comparison with one of the Georgia clays examined, were personally visited by him, in connection with a study of the Clays of the United States, begun several years ago; and the samples, from each locality, were personally and carefully collected, with the view to obtaining, as nearly as possible, an average, for the given locality, of the workable part of each clay-bed, under consideration. The experiments and analyses were, also, personally conducted. THE DEFINITION, OCCURRENCE AND DISTRIBUTION OF FIRE-CLAY The term, fire-day, is generally used, from its commercial significance, as a name for clays, which have refractory qualities, sufficient to enable them to resist the high temperatures, used in the technical arts, mostly in the construction of furnaces and of vessels, in which glass is to be made, zinc smelted, ores assayed, etc. ( r66) A CONPARJSOX OF CLA 1'S A pure clay is highly infusible; and the clays, selected for comparison with the Georgia clay, are those, which contain such small quantities of fluxing impurities, as to enable them to withstand high temperatures. As the clay occurs in nature, the lack of these impurities, detrimental to it as a fire-clay, may be due, either to their original absence, or to the fact, that they have been dissolved and removed, by natural processes. All clays probably originate, in the presence of these impurities; and transported clays may have, deposited with them, more or less of such; and it is probably due, in most cases, at least, to a final removal of deleterious compounds, that clays of high refractoriness exist. The conditions, favorable for the removal of the impurities, are largely, that the clay-bed shall be exposed, for a long time, to the influence of comparatively pure waters, charged with some solvent reagents, and shall be sufficiently porous, at least in some period of its existence, to allow the free percolat:::m ancl escape of these waters. GEOLOGICAL AND GEOGRAPHICAL OCCURRENCE Clays, which have been so situated, occur in many parts of the world, and have been commercially developed, largely in Great Britain, Germany, France and the United States of America, -less extensivelv in Sweden and other countries. -' In the United States, they occur in localities, scattered over the length and breadth of the country. Geologically, they arc practically confined to the Coal Measures, where they are most largely developed, and to the Cretaceous and Tertiary formations. The most extensively worked of these is the Allegany Coal Measure 168 A COMPARISON OF CLAYS basin; and, within its boundaries, the greatest development of the fire-clay industries is in Pennsylvania, Ohio and Maryland. The Illinois Coal basin is worked, in a number of localities, over a wide area. The outlying portion of this basin in St. Louis county, Missouri, is enormously developed within the city-limits of St. Louis, mostly in the vicinity of the suburb, Cheltenham. The coal basin, which extends southwestward from Iowa, furnishes an abundance of good fire-clay, and is most largely worked within the limits of Missouri. The Cretaceous formations furnish high-grade refractory clays, which are worked very extensively in the State of New Jersey, and in the neighboring portions of New York, on Staten and Long Islands. Beds of the Cretaceous are also worked very successfully in the States of Colorado and Georgia. The Tertiary formations are worked for fire-clays in the States of Texas, California and Florida. In one district, namely, that developed on the Kentucky and Ohio sides of the Ohio river, near Portsmouth, Ohio, a bed of fireclay is worked, which belongs to the Lower Carboniferous period. Fire-clays in the United States are worked, and form the basis of important industries, in New York, New Jersey, Pennsylvania, Ohio, Maryland, Georgia, Kentucky, Tennessee, Illinois, Indiana, Iowa, Missouri, Texas, Colorado and California; and it is probable, that, if fire-clays are not already mined in many other States, they soon will be. Among these are Michigan, West Virginia, North and South Carolina, Alabama and Arkansas. A COMPARISON OF CLAYS 169 CLAYS SELECTED FOR SPECIAL STUDY The clays, discussed in this chapter, were selected, on account of their significance, as furnishing, to some extent, typical samples from the most important fire-clay beds, when considered from the point of view of their commercial value, geological age, and geographical position. They come from the following localities:- Woodbridge, New Jersey Woodland, Pennsylvania Mount Savage, Maryland Canal Dover, Ohio Sciotoville, " St. Louis, Missouri Athens, Texas Golden, Colorado Carbondale, California Griswoldville, Georgia NEW JERSEY This State has long been noted for its clay industries. The center of development of these is in Middlesex county, I which lies just west of Staten Island Sound and Raritan Bay. The clay-beds in the Middlesex district belong to the Cretaceous formation, and occur at the bottom of the New Jersey Cretaceous series, where they are known as the Plastic Clays, a synonym of " Potomac," "Tuscaloosa" and "Trinity," terms used along the southwestward continuation of this formation. The Cretaceous strata occur, in surface distribution, as a broad belt, stretching I The geology of this region, the nature and origin of the clays, and the industries based on them, ' have been most admirably studied and described by the late Professor George H. Cook, State -Geologist, and his assistant, Mr. John C. Smock, since State Geologist, in a report, already referred to, which was published by the Geological Survey of New Jersey in 1878. A COMPARISON OF CLAYS across the State from Sandy Hook to Delaware Bay, having a northwesterly strike, and dipping gently to the southeast, beneath the Tertiary strata, and out under the Atlantic ocean. The Plastic Clay beds are lowest down in the series; and, consequently, they outcrop farthest west. There are but comparatively few places, where these clays actually outcrop at the surface, since they are often buried under many feet of sand and gravel drift. South of the region under discussion, within New Jersey, the claybeds are so completely covered by drift, as to be little exploited, or worked. Clays, belonging to this same formation, extend northeastward, and are worked, for commercial purposes, on Staten Island and Long Island, New York, and on Martha's Vineyard at Gay Head, in Massachusetts. In the two former places, they are mined for the manufacture of fire-brick; but, in the latter, for pottery and tile-making. The Southern extension of these clays furnishes material for many clay industries in a number of States, particularly in South Carolina and Georgia. In the Plastic Clays, there are three beds, which, although they are used commercially, for various purposes, are designated as "fire-clay," and furnish excellent material for the manufacture of refractory wares. These are the South Amboy, the Woodbridge and the Raritan fire-clay beds. A sample of clay from the bed at Woodbridge, was taken by the write~, as before stated; and the results from his study of it may be seen in the several comparative tables, near the end of this chapter. A COMPARISON OF CLAYS 171 MARYLAND 1 Maryland is the seat of numerous and important clay industries. Brick, terra-cotta, tile and pottery are manufactured largely, in the viCinity of Baltimore, where the clay is furnished by the Potomac and Columbia formations. Fire-clay is also mined, from these formations, at Baltimore, and at North East, in Cecil county. The most important fire-clay locality is, however, in the western part of the State, where the clay is obtained from the Coal Measures. The development of the clay is confined to Allegany county; and the locality, in general, is known as the Mount Savage Fire-clay district. The general geology of this district is closely related to that of Western Pennsylvania and Eastern Ohio. The Mount Savage Fire-clay district is situated in the western part of Maryland, and southwestern part of Pennsylvania. It is one part of the Carboniferous field, which extends, as already outlined, from Northeastern Pennsylvania, through Eastern Ohio, Maryland, West Virginia, Kentucky and Tennessee, into Alabama. Within this broader area, a large number of fire-clay beds are worked. Few of them, however, are continuous over any great extent of country; and none of them approach uniformity, in character and quality, throughout any considerable distance. Some beds are more persistent than others, in all these respects; and, among them, a few furnish exceptionally good clay. These have been developed mostly in Western Pennsylvania, Eastern Ohio, the northern part 1 The geological literature and notes of these fire-clays are confined essentially to various reports of the Pennsylvania and Ohio Geological Surveys; to a paper by the late Professor George H. Williams and others, in a book entitled "Maryland, Its Resources, Industries and Institutions," published for the Chicago Exposition; and to a paper on the manufacture of fire-brick at Mount Savage, Maryland, by Robert Anderson Cook, in Vol. XIV, Trans. Am. Inst. Min. Eng. 172 A COMPARISON OF CLAYS <>f Central Kentucky, and in Allegany, Maryland. They have been slightly developed in West Virginia, Tennessee and Alabama. The " Mount Savage bed," proper, is worked in Allegany {;Ounty, Maryland; in Bedford and Somerset counties, Pennsylvania, immediately north; and, it is said,1 in Cambria county, Pennsylvania, at Johnstown. The numerous other fire-clays worked, north and west of this region, appear to be in other beds in the geological scale. The fire-clays belong to the group, originally designated, in the Paleozoic formations, as No. XII, by Rogers, and known as the Pottsville or Seral Conglomerate. It belongs, geologically, in this region, at the bottom of the Coal Measures, just beneath the Lower Productive Measures, and above the Mauch Chunk Shales. The earliest and best known of the fire-clay works, in this region, .are those at Mount Savage. Other works; which mine the same bed, are at Frostburg, Maryland, and Hyndman, Bedford county, and Keystone Junction, Somerset county, Pennsylvania; possibly, also, at Williams station in the last named county. As before mentioned, the writer visited Mount Savage, and selected, from its day bed, a sample for study, the results of which may be seen in the tables of comparison, near the end of this chapter.. PENNSYLVANIA Pennsylvania is one of the leading fire-clay-producing States in the Union. Kaolin, in situ, is mined in the southeastern part of the State, and the transported clays, of several geological ages, in a 1 See report H H, 2nd Geol. Surv. of Penn., r875, p. 99 A COMPARISON OF CLAYS great many localities. The best known fire-clays are those, occurring in the Coal Measures, in the western part of the State. Beds, occurring at different horizons, are worked at different places. The clay, underlying the Freeport Upper Coal, exists in numerous places, as an excellent fire-clay, and has been mined extensively at numerous localities, the best known of which is Bolivar. It is also worked at several places in Fayette, Indiana, Beaver and Westmoreland counties. The Lower Kittanning Coal is often underlaid by a fire-clay, which is also extensively mined for a high-grade refractory material, at a number of places, both in Pennsylvania and Ohio. The workable part of the bed is usually six or seven feet thick, and thewhole bed varies in thickness, from ten to fifteen feet. It is mined in Fayette and Westmoreland, and, probably; in other counties. In some counties, it is said, that the Ferriferous Limestone Clay is worked as a fire"clay. The plastic clay, occurring immediately below the Clarion Coal-bed, is mined at Bolivar, on the Conemaugh river, and is used in admixture with non-plastic clays, in the manufacture of refractory materials. The Brookville coal under-clay(?) is mined at several places in Clearfield county; and, among other localities, at Brookville, in Jefferson county; Queen's Run and Farrandsville, in Clinton county; and Johnstown, in Cambria county. The two best known fire-clay districts are the Clearfield and the Mount Savage, which, as was stated in the notes on Maryland, extend into Pennsylvania. The results of the writer's investigation of the sample, taken from the clay bed at Woodland, Clearfield county. are to be seen in the comparison tables, near the end of this chapter_ 174 A COMPARISON OF CLAYS OHIO The clays of this State have been carefully studied by Professor Edward Orton, State Geologist of Ohio, and Mr. Edward Orton, Jr., who have made elaborate and comprehensive reports on their distribution, origin, nature and uses. I Clays for pottery, tile, sewer-pipe and brick-making are mined from the beds, belonging to several geological periods, at many different points in the State. The Clays of the Coal Measures, however, vastly exceed in importance those of all the other formations, and the so-called Kittanning Clays and Shales are the all-important clays of this series. The beds, which furnish the highest grade fire-clays, and are accessible, are limited, with few exceptions, to two districts- one, in the northeastern part of the State, covered largely by Tuscarawas county; the other, in the central part of the southern margin of the State, in Scioto county, which, considered as a clay district, extends across the Ohio river into Green and Carter counties, Kentucky. In the Tuscarawas county region, the fire-clay, worked, is the Lower Kittanning Under-clay, previously mentioned in the 1 notes on the Pennsylvania fire-clays. The occurrence of this clay has been admirably described by Mr. Orton, as follows:- "The first district of Kittanning clays, met, on entering this State from the east, is the yellow-ware beds of Liverpool and Wellsville. The vein, here, is plastic and easily mined, and is reached mainly through drifts. It underlies the Kittanning Coal, directly. The next district is the Jefferson County pipe-works, which line the Ohio river, for twenty miles, from Wellsville nearly to Steuben- I Vol. V, Geol. Surv. of Ohio, Report on Economic Geology. Ibid., Vol. VII, Part I, t893 A COMPARISON OF CLAYS 175 ville. The clay is here regularly excellent in quality, easily found, and at convenient levels for mining. It is rather sandy, or siliceous, quite hard at first, but quickly slacking on exposure; and it is plastic and readily moulded, after grinding. The clay extends up Yellow creek, beyond Irondale, where it still is of good quality, and is in constant use. In the northern part of Tuscarawas county, at Mineral Point, the Kittanning clay appears, in a new and valuable pha~e. It is found, as a very hard and fine fire-clay, suitable for making any refractory material. It is used for retorts, glasspots, brick of finest special grades, etc. It is found, about three feet below the Kittanning coal, separated from it by worthless clay. There can scarcely be a more beautiful or faultless stratum of clay, than the hard clay of this place. It lies in a band, three and one half feet thick, showing faces smoother, than the most regular coal; it is so hard, that chips from a pick-blow will cut the hands of the mmer. It is of a light-drab tint, burning to a light-cream color; it shows the blue, concentric venation of organic matter, noticed in the flint-clay of Sciotoville. The mining of this clay is carried along with the mining of coal, both being taken out of the same pit-mouth. The coal is usually worked first, and then the clay. There is enough plastic clay occurring with the flint, to allow its perfect working. This bed of hard clay marks the Kittanning horizon from Magnolia." The Scioto county clay belongs beneath the Maxville, or Subcarboniferous Limestone, coal (?), and is the lowest fire-clay bed, in the Geological scale, worked in this country. This clay has been described by Mr. Orton/ as follows:- "The deposit is first found in the tops of intersecting ridges near Portsmouth, occasionally overlain by nodules of limestone, but no 1 Economic Geology of Ohio, Vol. V, "Clay Deposits," page 661. 176 A COMPARISON OF CLAYS coal; at Sciotoville, eight miles eastward, the hills are all high enough to hold it, and its best development is here; at Webster, thirteen miles further on, it is at drainage-level; and, shortly after, dips under the surface. On the Kentucky shore, and for forty miles to the southeast, it has a very heavy development. The clay runs, from one foot to five feet thick, averaging two feet, six inches. It is benched, where practicable; drifted, where necessary; and all is mined by powder. It is grayish-drab in color, full of blue organic stains, but of remarkable purity and excellence. It is very hard and flinty; but it runs soft in places, so that plastic clay need not, as a rule, be imported. "Another small development of this clay is found near Logan, Hocking county, where it supports the manufacture of a good firebrick." Two samples of clay from this State were investigated, by the writer. They were taken, respectively, from Canal Dover and Sciotoville. The results may be seen in the tables of comparison, near the close of this chapter. MISSOURI Missouri completes a quintette of States, with those already aiscussed, remarkable for their clay deposits. These abound within her borders, in endless variety, and are suitable for nearly all the uses, to which clay is put. Her fire-clays are wide-spread and varied, in manner of occurrence. They may be grouped for convenience of study, according to their geological occurrence, into three classes, which may be designated as the St. Louis, Crawford and Audrain Clays. A COMPARISON OF CLAYS 177 The first and most important of these classes includes those, which are mined in the city of St. Louis, and which belong geologically to the Coal Measure basin, lying in St. Louis county and city, with the exception of a small area in St. Charles county, just across the Missouri river. This Coal Measure basin may be considered as an outlier of the Illinois Coal basin, since it is geologically nearer that basin, than the one lying west of it. It will be discussed more in detail, below. The next class, the Crawford clay, includes a large number of more or less isolated pockets of fire-clay, occurring, unconformably, in cavities and along old valleys, among the Silurian and, possibly in some cases, Devonian and Lower Carboniferous rocks. These pockets of fire-clay are distributed over a number of counties, occupying about the center of the eastern half of the State, its northern boundary being but a few miles north of the Missouri river. They are of uncertain geological age, and are possibly the remnants of a once very extensive formation in this region. They are to be found mostly in the minor lateral valleys, along the borders of the greater ones, and apparently always near the tops of the valley sides. They sometimes occur in shallow pockets along the top of the divides, this being especially noticeable in Gasconade county, where they occur over a wide area. The greatest thickness of the clay, seen by the writer, was at Regina, Jefferson county, where a pocket had been opened, to a depth of sixty feet. Borings have been made in pockets, seeming to belong to this class, which penetrated the clay to a depth of 12 5 feet. The clay is usually of a cream-color; but it is often mottled with purple and reddish tints, which are organic stains, and which readily disappear, on ignition. It is hard and brittle; breaks with a conchoidal fracture; and weathers concentrically, breaking up indefinitely A COMPARISON OF CLAYS into sharp, angular fragments. It is mined (as a fire-clay) mostly in Montgomery, Warren, Franklin, Crawford and Phelps counties, for shipment only, going to fire-brick works in St. Louis, Chicago and eastern cities, where it is used in connection with more plastic clays, to diminish their shrinkage. In one locality, near Union in Franklin county, the upper four or five feet of this clay is plastic. In a great many other places, it occurs as white clay, brilliantly mottled with reddish tints, and sometimes stained very dark purple. It is comparatively soft, and free from sand, and has a smooth, soapy feel; and it is cut with a knife, in an indescribably smooth, soft way. The third class, Audrain clay, most highly developed in Audrain and Callaway counties, belongs in the Coal Measure basin, extending southwestward from Iowa, across Missouri, and occupying the greater part of the northwestern half of the State. The workable fire-clays of this class are confined, largely, to the southeastern border of this area. They were developed at the time of the writer's study of this region, in I 890, only at Fulton, Mexico, Ladonia and Vandalia. The Fulton clay (in Callaway county) may possibly belong to the second class, described above. At Mexico, this fireclay is largely developed, as it is, also, at Vandalia; but it is not certain, that the clay at these two places belongs to the same bed. S'l'. LOUIS, MISSOURI The St. Louis fire-clays are, by far, the best known m Missouri. They are the only ones from the State, that are represented in this comparative study. The following descriptive notes of the St. Louis locality and its A COMPARISON OF CLAYS 1 79 clays are reproduced, largely, from a report, published by the writer in 1891.1 Geologically speaking, St. Louis has three local sources of clay. These are the Coal Measures, the Quaternary deposits, and the residuary product of decomposing limestone. Of the two latter, the Quaternary deposits only are of much value; and these, not being used as fire-clay, will not be discussed. THE CoAL MEASURE CLAYS The Coal Measures, which have an area, approximating two hundred square miles in St. Louis county and city, carry practically an inexhaustible supply of potter's, sewer-pipe and fire clays, of which the best of the latter have long been noted for their high refractory qualities. The mining and manufacturing of these clays has been carried on, for many years, and, to a large extent, in the immediate neighborhood of St. Louis. The fire-clays occur in beds, ranging from a few inches to seven, or more, feet in thickness. They are occasionally so near the surface, as to be mined by drifts; but usually they have to be sought by shafts. The deepest of these in St. Louis is I 20 feet, from the surface of the ground to the bottom of the clay bed. These clays, even in the same bed, vary largely, in character and composition. They are, usually, grayish in color, and very hard, when mined; but, after exposure to the weather for a variable time, the clay softens, or slacks, and falls into a loose mass of finely divided particles. Pyrite occurs in the clay, generally in aggregations, and either close to the top or bottom of the clay bed, so that it may be avoided, to a great extent, in mining. The best grades of clay, those suitable for making glass-house pots, in a raw and 1 Bulletin No.3, Geological Survey o[ Missouri. ISO A COMPARISON OF CLAYS unwashed condition, are of limited occurrence, and are not continuous in the bed, in which they are found. They may be considered as existing in "pockets"; but the transition, from the best clay into the poorest grades, is gradual. The fire-clay is mined in chambers, which are kept well timbered, until they have been carried as far as possible, when the timbers are removed, and the roof is allowed to drop in, the debris forming a wall for a new chamber, which will be run along the side of the old one. There are probably several miles of these chambers within the city of St. Louis. Immediately overlying the clay, is, generally, a hard shale or a bed of sandstone, which makes a very good roof. At some of the mines a bed of coal lies just above the fire-clay; but it rapidly thins out, and almost quite disappears, at other mines. The use of powder is a necessity in the mining, on account of the hardness and density of the clay. Two samples from the St. Louis fire-clays were taken, respectively, from the Evens & Howard mines and the factory of the Christy Fire-clay Co., the sample from the latter being of their washed pot-clay. The tables of comparison, near the end of this chapter, show the results of the writer's investigations. COLORADO The Colorado clays are representative, in a general way, of the clays, occurring in the Eastern Rocky Mountains. They belong mainly to the Cretaceous and Paleozoic formations, the best and most used being the Upper Cretaceous. These clays have been so little prospected and developed, in other regions in this part of the country, that no comparison can be made; and it cannot be asserted, A COMPARISON OF CLAYS 181 although it is probable, that clays, belonging to the same horizon as those worked for refractory materials in Colorado, occur of equal purity elsewhere. The fire-clays of this State furnish, largely, the refractory material for the furnaces in the Rocky Mountain region. They are taken from the Dakota member of the Upper Cretaceous formation, which flanks, with its upturned strata, the eastern margin of the mountains, and makes the "bordering reefs," locally known as "hog-backs." The sample taken from the fire-clay bed at Golden, was studied by the writer, and his results are included in the tables of comparison, near the end of this chapter. CALIFORNIA Clays are mined in a number of places, in different parts of the State; but little has been published, concerning their geological occurrence and age. They, probably, are mostly from the Tertiary formations, which are distributed in the Sacramento and San Joaquin valleys and the minor valleys of the Coast Range. These clays are used largely, for the manufacture of pottery, sewer-pipe etc.; and but one locality has been found to produce a refractory clay. This is in Amador county, along the foot-hills, and near the eastern border of the Tertiary strata, which occupy the great valley of California, and which are thought to be of Pliocene age. The clay is mined, in the vicinities of lone and Carbondale, part of it being locally manufactured into pottery, but most of it being shipped to Sacramento and San Francisco, where it is manufactured into fire-brick and various other products. 182 A COMPARISON OF CLAYS The sample, taken by the writer, from the clay banks at Carbondale, was submitted to investigation, the results of which are given in the comparison tables. TEXAS Texas, like California, has geological formations, furnishing an abundance of clay material, which has been but little worked. The most important of the clay-producing formations, omitting from consideration the possible value of kaolin deposits among the granitic rocks, are the Cretaceous and Tertiary, which occupy the greater part of the State. The most valuable clays, however, are confined to eastern localities, and belong to the Miocene, or Fayette, division of the Tertiary. While beds, from this geological horizon, are mined at a number of places, for pottery and the commoner uses, there are only three localities, where they are worked as fire-clay. These are in Henderson, Limestone and Fayette counties, the beds worked in the two latter counties being assigned to the so-called Timber Belt beds. I The Fayette clays are referred to, in a report by the State Geologist, as follows:- 2 "The Fayette beds contain light-colored clays, many of which are pure white. These beds of clay not only underlie and overlie the middle beds of Fayette sands; but they are also found interbedded with that series." Many analyses have been made of clays of various portions of I Second An. Rep . State Geologist of Te:~. 0'" v b/) '" '""@ 'uii 'b..!..J 0 .0 0 E-< ... >., . s:: ;: ~ 0 0u if) ------~ v b/) "> ' J (;j Alumina, Al 0 23 39 13 36.g8 28.q 37 27 2 I. J6 3 I.75 31.72 23.26 40.04 20.7 I 38. I4 a ~ Free Silica, or Sand . I. 23 I. 92 26.81 o.6I 3832 I7.00 5 22 31.82 0.3I 3706 59 ~ Ferric Oxide, Fe 0 2 3 Lime, CaO . 0.45 0.99 I. 67 1.48 2. 72 O.I8 O.IS 0.49 o.s8 o.6I 1. o6 0.36 324 0.87 0.36 o.6s 2.40 O.IS I.OI 1.3 I o. 22 trace ~:... Magnesia, MgO . 0. I I o.83 0. 28 0.62 0.30 0.04 0.23 0.42 0. I7 0.39 o.q ~ Potash, K 0 2 Soda, Na 0 . 2 Total o.sl 0. 2I o.IS o.89 0.86 0.16 0.48 054 0.30 o.69 0.49 - -o.6-3 - 0.28 -- - 0.46 -- -O-.I9 - 0.88 --3 , 0.48 --- 0.45 --- 079 - 0.38 -- - -03-9 - 0.42 -- I00.45 g8. 75 IOO. 25 9937 99.82.100.15 98. I I g8.484 IOO. 14 9946 1oo.g8 Clay Base 2 9734 9437 7039 95-00 s6. 13 8o.s4 91.01 6r. 02 9643 59 7 92.69 Fluxing Impurities . I. 88 2.46 345 1 Based on Clay, dried at 10o C. 3 Contained, also, Sulphur, .12, and Sulphur Trioxide, .56. 374 5 37 2.58 2. 27 564 340 2.70 2-39 2 Approximate. 00 4 Contained, also, Sulphur, .31, and Sulphur Trioxide, 35 I86 A COil1PARISON OF CLAYS TABLES OF COMPARISON CLAY BASE PRESENT Griswoldville, Georgia ______ ---- 9734 per cent. 2 Sciotoville, Ohio ___ ------------- g6.43 " " 3 Woodland,Penn.. _____________ 95.00" 4 Woodbridge, N. ]. --------- - 9437 " " 5 Mount Savage, Md. _ ---------- 92.69 " " 6 Golden, Colo. ------------ .... 91.0I " " 7 Carbondale, Cal.. __ - -- . --- . - -- So. 54 " " 8 Canal Dover, Ohio--------- -- 70.39 " " 9 Evens & Howard, St. Louis, Mo. 61.02 " " IO Athens, Texas ------- -- -- -- 59-70 " " I I Christy, St. Louis, Mo . . --. ---- 56. I 3 " " SAND PRESENT Sciotoville, Ohio______________ 0.3 I per cent. 2 Woodland, Penn.. _____________ o.6I " " 3 Griswoldville, Georgia--------- 1.23 " " 4 Woodbridge, N. ]. ___ --- _____ . 1.92 " 5 Golden, Colo. ________ ------- 5.22 " 6 Mount Savage, Md. ----------- 5.90 " 7 Carbondale, Cal. ________ .. ____ I7.00 " " 8 Canal Dover, Ohio------ _____ 26.8I " 9 Evens & Howard, St. Louis, Mo. 31.82 " " IO Athens, Texas--_------------ 37.06 " " II Christy, St. Louis, Mo.-------- 38.32 " " A COMPARISON OF CLAYS FLUXES PRESENT Griswoldville, Georgia ________ _ 1.88 per cent. 2 Golden, Colo. ________________ _ 2.27 " " 3 Mount Savage,Md. ___________ _ 2.39 " 4 Woodbridge, N.J. _____________ 2-46 " 5 Carbondale, Cal. ______________ _ 2.58 " " 6 Athens, Texas--------- __ ------ 2.70 " " 7 Canal Dover, Ohio 345 " " 8 Sciotoville, " ____ _ _______ 340 " " 9 Woodland, Penn. _____________ _ 3 74 " " 10 Christy, St. Louis, Mo. _______ _ 537 " " I I Evens & Howard, St. Louis, Mo. " " SCALE OF RELATIVE DENSITIES (No. r, LEAS'!' DENSE) Griswoldville, Georgia 2 Woodbridge, N. J. 3 Athens, Texas 4 Carbondale, Cal. 5 Canal Dover, Ohio 6 Golden, Colo. 7 Mount Savage, Md. 8 Sciotoville, Ohio 9 Woodland, Penn. 10 Evens & Howard, St. Louis, Mo. I I Christy, St. Louis, Mo. I90 A COMPARISON OF CLAYS TENSILE STRENGTH (WET) Christy, St. Louis, Mo.- Strongest 2 Woodbridge, N.J. 3 Athens, Texas 4 Woodland, Penn. 5 Evens & Howard, St. Louis, Mo. 6 Griswoldville, Georgia 7 Carbondale, Cal. 8 Sciotoville, Ohio 9 Canal Dover, " 10 Golden, Colo. I I Mount Savage, Md.- Weakest TENSILE STRENGTH (DRY) Christry, St. Louis, Mo. ------ I 56lbs. per sq. in. 2 Evens & Howard, St. Louis, Mo. I28 " " " 3 Athens, Texas _____________ I I 5 " 4 Golden, Colo. __________ -- - 6o " " " " "" 5 Mt. Savage, Md. ______ 49 " " " " 6 Canal Dover, Ohio _____ - 47 " " " 7 Sciotoville, Ohio __ - ___ . _____ 38 " 8 Griswoldville, Ga. ________ -- -- - 32 " " "" 9 Woodland, Penn. ________ --. 3I " " " " IO Woodbridge, N.J. - - ------ 24 " I I Carbondale, Cal. _________ - _ I6 " " "" A COMPARISON OF CLAYS 191 ScALE OF PENETRABILITY (WET) No. I, Least Penetrated Mount Savage, Md. 2 Athens, Texas 3 Christy, St. Louis, Mo. 4 Woodbridge, N. J. 5 Golden, Colo. 6 Griswoldville, Georgia 7 Carbondale, Cal. 8 Evens & Howard, St. Louis, Mo. 9 Canal Dover, Ohio 10 Sciotoville, Ohio I I Woodland, Penn. ScALE OF RELATIVE HARDNEss (AS CLAY OCCURS IN THE FIELD) Carbondale, Cal. - Softest 2 Athens, Texas 3 Griswoldville, Georgia 4 Woodbridge, N. J. 5 Christy, St. Louis, Mo. 6 Evens & Howard, St. Louis, Mo. 7 Golden, Colo. 8 Sciotoville, Ohio 9 Canal Dover, " IO Woodland, Penn. I I Mount Savage, Md. -Hardest 192 A COMPARISON OF CLAYS The foregoing tables show, of the Georgia fire-clay, that, of the whole series, it is the most refractory, and contains the largest amount of clay base, the smallest amount of fluxing impurities and nearly the smallest amount of sand. It is one of the softest clays in the series; is the least dense; and absorbs the largest percentage of water. As regards shrinkage on drying, it stands intermediate in the series; but there is no further shrinkage on burning, which is true of only one other sample in the series, namely, that from Athens, Texas. In tensile strength, both dry and wet, and in penetrability, it is intermediate. In most of the important properties for a fire-clay, it is remarkable. There are few fire-clays, however, which have such a range of properties, as makes them suitable for manufacture, without a mixture of other clays; as, for instance, to make them more plastic, less plastic, more refractory, shrink less, or possess a greater tensile strength and "body." Its one defect is, that it crackles, on burning; but this can be easily remedied. -- APPENDIX BY W. S. YEATES, STATE GEOLOGIST Dr. Ladd having failed to furnish the "list of publications," referred to, on page 36, I have compiled a bibliography of such publications on the subject of Clay and its manufacture, as seemed desirable for this work. For an excellent and very extensive bibliography, the reader is referred to the work of Dr. ]. C. Bran- ner, mentioned in the list below. BIBLIOGRAPHY Anderson, F. Paul. Paving Bricks. Tested for Compressive Strength and Absorption. The Digest of Physical Tests and Laboratory Practice, Vol. I, No. 2, pp. Io8-I33 Philadelphia, April, I 896. Barber, Edwin A. The Pottery and Porcelain of the United States. New York, I893 Barus, Carl. Thermal Effects of the Action of Aqueous Vapor on Feldspathic Rocks (Kaolinization). School of Mines Quarterly, Vol. VI, No. I, pp. I-231. Kaolinization (in Geology of the Comstock Lode and the Washoe District, Mont.) U. S. Geol. Surv., Vol. III, pp. 290-308. Washington, I882. Subsidence of Fine Solid Particles in Liquids. Bull., U. S. Geol. Surv., No. 36. Washington, 1887. (193) iJiBLI6Ci?APliY Becker, G. F. Geology of the Comstock Lode. Mon., U.S. Geo1. Surv., Vol. III, Washington, 1882. (Decomposition of Feldspar, p. 385; Kaolinization, p. 388; Clays, p. 394; Thermal Effect of Kaolinization, pp. 397-400. ). Bischof, C. Die Feuerfesten Thone. Leipzig, 1895. Blatchley, W. S. A Preliminary Report on the Clays and Clay In- dustries of the Coal-bearing Counties of Indiana. 2oth An. Rep. (1895) of the Dept. of Geology, Indiana, pp. 24-179. Indianapolis, 1896. Blue, A. Vitrified Bricks for Pavements. 3rd An. Rep., Ontario Bureau of Mines, p. 103. Toronto, 1893. Branner, J. C. Bibliography of Clays and the Ceramic Arts. Bull., _U.S. Geol. Surv., No. 143, pp. 1-114. Washington, 1896. Brewer, W. H. On the Suspension and Sedimentation of Clays. Am. Jour. Sci., 3rd Ser., Vol. XXIX, pp. 1-5. 1885. Abstr., Jarbuch fur Mineral., Vol. I, p. 414. 1888. Calvin, Samuel. Geol. of Allamakee County, Iowa. 3rd An. Rep., Iowa Geol. Surv., 1894. Des Moines, 1895. (Clays, pp. 94-96.) Geology of Jones County, Iowa. Iowa Geol. Surv., An. Rep., Vol. V, 1895. Des Moines, 1896. (Clays, pp. 107-109. ). Chamberlin, T. C. Color of Milwaukee Bricks and Analyses of Clays. Geol. Rep. of Wisconsin, Vol. I, p. 120; Vol. II., pp. 235. 236. --------and Salisbury, R. D. The Driftless Area of the Upper Mississippi. 6th An. Rep., U. S. Geol. Surv., for the year 1884-85, pp. 199-322. Washington, 1885. (Analyses of Residual and Glacial Clays, p. 250.). Chase, Charles P. Paving Bricks and Brick_Pavements. Engineer- ing News, Vol. XXIV, July 19, p. 55; July 26, p. 70, r89o. Clarke, F. W. (Analyses of Eight) Clays, etc., from Martha's Vine yard, Mass. Bull., U. S. Geol. Surv., No. 55, pp. 89-90. Washington, r889. Collett, John. Kaolin (in Owen County, Indiana). 7th An. Rep., State Geologist, p. 358. Indianapolis, r876. Clays (of Indiana). IIth An. Rep., State Geologist, p. 2r. Indianapolis, r 882. Clays and Kaolin (in Indiana). r 2th An. Rep., State Geologist, p. 24. Indianapolis, r883. BIBLIOGRAPHY 195 Cook, Geo. H. Clays of New Jersey. Geol. Surv., New Jersey, pp. 48-69. 1878. Cook, R. A. The Manufacture of Fire-brick at Mt. Savage, Md. Trans., Am. Inst. Min. Eng., Vol. XIV, p. 701. Eng. News, Vol. XV, p. 227, April 10, I886. Eng. and Min. Jour., New York, March I3, I886. Cox, E. T. Porcelain, Tile and Potters Clays. Indiana Geol. Surv., p. I 54 I878. Davis, Charles Thomas. A Practical Treatise on the Manufacture of Bricks, Tiles, Terra-cotta etc. Philadelphia, 1884; 2nd ed., I889. Day, David T. Pottery. Mineral Resources, U. S., 1889-90, pp. 44I-444 Day, Wm. C. Structural Materials. Mineral Resources, U. S., I886. (Bricks etc., pp. ss6-s8o.) Structural Materials. Mineral Resources, U. S., I887. (Bricks etc., pp. 534-551.) Structural Materials. Mineral Resources, U. S., I888. (Bricks etc., pp. 557-575-) Engle, G. B., Jr. Enameled Bricks. Am. Arch., Vol. XLIII, p. I29. I894 Ferry, C. Fire-clays in New Jersey. The Iron Age, Vol. LV, p. 332. High Silica Fire-brick. The Iron Age, Oct. ro, 1894. Value of Practical Tests of Refractoriness. The Iron Age, Oct. 3 I, 1894. Griffiths, H. H. Clay Glazes and Enamels. Indianapolis, I89S Harden, E. B. Report on Fire-clay. An. Rep., Geol. Surv., Penn- sylvania, I88s, pp. 239-249. Hay, Robert. The River Counties of Kansas. Trans., Kan. Acad. Sci., Vol. XIV, 1893-'94. Topeka, 1896. (Clays, pp. 243-245 ; 252-253; 258.). Henderson, J. T. Commonwealth of Georgia, Atlanta, r885. (Clay, p. 132 ). Hill, Robert T. Clay Materials of the United States. Mineral Re- sources, U.S., 1891, pp. 474-528; the same for I892, pp. 712- 738; the same for 1893, pp. 6o3-6J7. Washington, 1893, I893, 1894 Hofman, H. 0. Further Experiments for Determining the Fusibility of Fire-clays. Trans., Am. Inst. Min. Eng., Vol. XXV, 1895; also Separate, 15 pp. 196 BIBLIOGRAPHY Hofman, H. 0., and Demond, C. D. Some Experiments for De- termining the Refractoriness of Fire-clays. Trans., Am. Inst. Min. Eng., Vol. XXIV, pp. 42-66, 1894; also Separate, 25 pp. Holmes, J. A. Notes on the Kaolin and Clay Deposits of North Carolina. Trans., Am. Inst. Min. Eng., Vol. XXV, pp. 929-936. New York, 1896. Irelan, L. Pottery. 9th An. Rep., California State Mineralogist, pp. 240-261. Sacramento, 189o. Irving, R. D. The Mineral Resources of Wisconsin. Trans., Am. Inst. Min. Eng., Vol. VIII, pp. 502-5o6. x879-'8o, (Bricks, Clays and Kaolin.). Johnston, W. D. Clays. 9th An. Rep., State Mineralogist of Cali- fornia, pp. 287-308. Sacramento, 189o. Kennedy, W. Texas Clays and Their Origin. Science, Vol. XXII, No. 565, pp. 297-300 Dec. I, 1893 Kennicutt, L. P., and Rogers, John F. Fire-clays from Mt. Savage, Allegany County, Maryland. Jour. Analyt. and Applied Chemistry, Vol. V, pp. IOI, 542-544, October, 1891; Abstr., Jour. Iron and Steel Inst., Vol. I, p. 306, 1892. Kerr, W. C. Geology of North Carolina, Vol. I, pp. 296, 297. 1875 Ladd, G. E. The Clay, Stone, Lime and Sand Industries of St. Louis, Mo., City and County. Bull., Geol. Surv. of Missouri, No. 3, pp. 5-37. St. Louis, 189r. Notes on the Clays and Building Stones of Certain Western Central Counties, Tributary to Kansas City. Bull., Geol. Surv. of Missouri, No. 5 Jefferson City, 1891. Langenbeck, K. Chemistry of Pottery, p. 198. Easton, 1896. Lesley, J. P. Kaolin Deposits of Delaware and Chester Counties, Penn. An. Rep., Pennsylvania Geol. Surv., p. 571. x885. Leiber, 0. M. Clays. 1st An. Rep., Surv. of South Carolina, pp. 97-99. Columbia, 1858. McCreath, A. S. Analyses of Clays and Fire-bri~ks. Rep. MM., 2nd Geol. Surv. of Pennsylvania, pp. 257-279. .Harrisburg, r879. Analyses of Fire-clays. Rep. l\f3, 2nd Geol. Surv. of Pennsylvania, pp. 95-97. Harrisburg, 1881. McGee, W J Brick and Pottery Clays of the Columbia Formation. Report of the Potomac Division, qth An. Rep., U. S. Geol. Surv., 1892-'9-J, Part I, pp. 2_JI-2_J2. Washington, 1893 BIBLIOGRAPHY 197 Mell, P. H. The Southern Soapstones, Kaolin, Fire-clays and Their Uses. Trans., Am. Inst. Min. Eng., Vol. X, p. 322. (Fire-clay in Alabama). Abstr. in Trans., North of Eng. Inst. Min. Eng., Vol. XXXIII, p. 22. 1883-'84. Orton, Edward. The Clays of Ohio, Their Origin, Composition and Varieties. Rep., Geol. Surv. of Ohio, Vol. VII, Part I, Economic Geology, pp. 45-68. Norwalk, 1893. Orton, Edward, Jr. The Clays of Ohio and the Industries Estab- lished upon Them. Rep., Geol. Surv. of Ohio, Vol. V, pp. 643-721. Columbus, r884. The Clay Working Industries of Ohio. Rep., Geol. Surv. of Ohio, Vol. VII, Part I, Economic Geology, pp. 69-254. Norwalk, 1893. Periodicals. Thonindustrie Zeitung, Berlin, Germany. Ries, H. Clays of Hudson River Valley, roth An. Rep. of New York State Geologist. 1890. Notes on the Clays of New York State and Their Economic Value. Trans., N.Y. Acad. Sci., Vol. XII, pp. 40-47. December, r892. Clay. The Mineral Industry, 1893; Vol. II, pp. r65-2ro. New York, 1894. Technology of the Clay Industry. r6th An. Rep., U. S. Geol. Surv., 1894-'95, Part IV, pp. 523-575. Washington, 1895 Clay Industries of New York. Bull., N.Y. State Mus., Vol. III, No. 12. Albany, March, 1895 Pottery Industry of the United States. I 7th An. Rep., U. S. Geol. Surv., Part III, p. 842. The Clays of Florida. qth An. Rep., U.S. Geol. Surv., Part III, p. 871. Clays of Alabama. Bull., Ala. Geol. Surv. 1897. - - - - The Clay Working-Industry in 1896. 18th An. Rep., U. S. Geol. Surv., Part V, p. 1,ros. 1897. The Ultimate and Rational Analysis of Clays and Their Rel- ative Advantages. Trans., Amer. Inst. Min. Eng., Vol. XXVII. Russell, I. C. Sub-aerial Decay of Rocks. Bull., U.S. Geol. Surv., No. 52, pp. 39-43- (Characteristics of Residual Clays.). Shaler, N. S. The Brick-making Clays of Massachusetts. 16th An. Rep., U.S. Geol. Surv., 1894-'95 Part II, pp. 324-326. Washington, r895. 198 BIBLIOGRAPHY Smith, E. A. The Clays of Alabama. Extr., Proc. Alabama Indus. and Sci. Soc., Vol. II, pp. 33-42, 1892. Smock, J. C. Mining Clays in New Jersey, Trans., Amer. Inst. Min. Eng., III, p. 211. 1874-'75. Fire-clays and Associated flastic Clays, Kaolins, Feld- spars and Fire-sands of New Jersey. Trans., Am. Inst. Min. Eng., Vol. VI, p. 177 el seq., 1877-'78. Eng. and Min. Jour., New York, Vol. XXV, pp. 185, 2oo. 1878. , New Jersey Clays, Ibid., Vol. VI, p. 177 1879. Spencer, J. W. Clays. Paleozoic Group of Georgia, Geol. Surv. of Georgia, p. 276. Atlanta, 1893. Stokes, H. N. Analysis of Kaolin from Georgia Side of Savannah River, near Augusta. Bull., U. S. Geol, Surv., No. 78, p. 120. Washington, 1891. Struthers, J. Le Chatelier Thermo-electric Pyrometer, School of Mines Quarterly, Vol. XII, p. 143, and Vol. XIII, p. 221. Tarr, Ralph S. Economic Geology of the United States. New York, 1894. (Clays, pp. 399-402.). Thompson, Maurice. The Clays of Indiana. 15th An. Rep., State Geologist, pp. 34-40. Indianapolis, 1886. Tucker, Thomas. American Porcelain. Jour. Franklin Inst., Vol. XXV, p. 43 1853. Vulte, H. T. Method of Analyzing Clays. Bull., N.Y. State Mus., Vol. III, No. 12, pp.- 141-143. Albany, March, 1895. Watts, W. L. Placer County (Cali.) 1Ith Rep., State Mineralogist, pp. 319-322. Sacramento, 1893. (Clay Analyses.). Wheeler, H. A. The Calculation of the Fusibility of Clays. Eng. and Min. Jour., New York, Vol. LVII, pp. 224-225. March 10, 1894. Abstr., Jour. Iron and Steel Inst., Vol. LXV, pp. 43D- 432 I894 The Fusibility of Clays. Paving and Municipal Engineering, Vol. VI, pp. 200-204. May, 1894. Vitrified Paving Brick. Indianapolis, 1895. Clays of Missouri, Missouri Geol. Surv., Vol. XI, pp. 57-67. 1896. Clays and Shales on the Bevier Sheet. Report on the Bevier Sheet. Missouri Geol. Surv., Vol. IX, pp. 57-67. Jefferson City, 1896. })JiJilock.APiiY Willis, Arthur W. Fire-clay. Watt's Dictionary of Chemistry, Vol. II, pp. 65 r-653. London and New York, I869. Williams, Samuel G. Applied Geology. New York, 1886. (Fie- tile Materials, .PP 3 I 9-333) Winchell, N.H. Geol. and Nat. Hist. Surv. of Minnesota. Miscel- laneous Publicatio~s, No. 8, pp. 26-3 I. St. Paul, I88o. (Cream Colored Brick, p. 28.) Winslow, Arthur. Report on the Higginsville Sheet. Missouri Geol. Surv., Vol. IX, Jefferson City, I896. (Clays and Shales, pp. 92-95) Worthen, A. H. Economic Geology of Illinois, Vol. I, pp. 278, 453, 470, 496; Vol. II, pp. 55, 303, 3 I 6; Vol. III, p. 235. Young, Jennie J . . Ceramic Art. New York, 1878. INDEX A Butler, Clay Openings at, .. 96 Advisory Board, The, . ---District, The, ...... 3 .. ... 95- 97 Analyses of Georgia Clays, c 108, 115, 126, 133, 135, 139, 146, 185 Anderson, George, The Brick-works of, . 105 California, General Remarks on the Clays ~~~x .......... . ..... ~.m of, ... 181- 182 Augusta Brick Co., The Brick-yard Campfield, H. F., Geological Section on the of the, . .152- 153 Property of,. .. ..... 160 ---- Clays, The,..... .151- 154 Carr's Station, Potomac Clay at,... .148, 150 ----,Potomac Clay near,. 150 Central of Georgia Rail way, Clay Deposits ---- Region, The, . . . . ... 150 along the,. . . . . . . ...... 103, 105, 111, 128, 131, 137 - - - - Southern R. R., Clays along the,. 150 Chalker, Clay Exposures near,. 150 ----,The Clay Industry of, ......... 152- 154 ---,Exposure of Clay at,.... 151 chalk Hill. . . . . . . . . . . . . .13o- 131 B Chemical Analysis of Clays, The, . . . . 78- 79 - - - - Analyses of Georgia Clays, Baldwin County...... 137 108, 115, 126, 133, 135, 139, 146, 185 Barns, Dr. Carl, Cited . . . . . . . . . . . . . . 58 - - - -Analyses, Comparative Table of, . 185 Becham, J., The Pottery of,. 100 Chemisches Labo..atorimn filr Thonindustrie, ----, S., The Pottery of, . . . . . . 100 Clay-testing Furnace Manufactured by ----, W., The Pottery of,.. 100 the, Described. . .. 61- 62 Behavior of Clays with Reference to Heat, Classificatiorf of Clays . . ..1o- 12 Experiments on the,... . .. 58- 78 Clays, Geological and Geographical Occur- rence of, .. . .. .. . .. . . ...... 167- 168 The, .. .. .. .. .. .. .. .. .. .. 34- 3.~ Clay Research by Various States.. 9 Behavior of Clays with Reference to Water, Clays Selected for Study and Comparison .. 169 Summary of Results ........ 56- 57 Coastal Plain, The, . . . ........85- 91 Colorado, General Remarks on the Clays Tests of the, . .44- 57 of,..... ..186- 181 Columbia Formation, The,... . ........ 88- 91 The,.. .. .. 2o- 34 Columbus .. ... .. .. ... 91- 94 Belair, Clay Deposits along the Georgia -----,Clay Industries at,.... .93- 9! Railroad East of,.... . ...... 162 Comparison between a Georgia Clay and ---, Description of the Crystalline Rocks Other Well Known Clays of the United at,. . . . .. 159- 160 States .. . .166- 192: ---,Fire-clay Deposits between Grove- , Tables of,.. . .186- 191. town and,.. .. .. 161 Composition of Clays.. ..15- 18; Berry's, G. 0., Works. 94 Cook, Prof. Geo. H., Cited.. . . 75, 169 Bibliography. . .193- 199 Crawford County Localities, The,.. 97- 100 Big Sandy Creek.. 127 , The Small Potteries ----- District, The,. Bischof, Cited ....... . .. 127- 128 in,. .74-75, 76 Cretaceous Period, The, . .99- 100 .86- 87 Blake, G. J., The Brick-works of,. 105 Bond's Store, Potomac Clay near,.. 137 D Boswell, Wilbur, The Plant of, .. 153 Davis, John, Potomac Clay on the Farm Burned Clay Products, List of,. 37 of,. .129- 130 Bussell, J. M., The Pottery of, ... 151 Definition and Classification of Clays .... 9- 12. (2o1) 202 .INDEX Degree of ConsOlidation of Air-dried Clay, Determination of the,. 47 Dent, The Small Potteries near,.. 100 Dickson, Thomas, The Pottery of,. 100 Dry Branch, Occurrence of Clay at,. 134 E Earnest & Co., A. C., The Brick-works of,. 105 F Georgia Railroad, Clay Deposits West of Grovetown along the, ... 166 -'------, Potomac Clay along the,..... . . 148, 150 Glascock County, Potomac Clay in, ........ 150 Gordon Road, The Clays along the, .116- 118 Griswoldville . . . 108 Grovetown District, The, .. . .155- 158 , Fire-clay Deposits l!etween Belair and,. . ..... 161 :Fall Line Belt, General Aspect of the, ... SQ- 91 H ----Clays, Eastern Extension of the,. 150 - - - - - - - - - , O r i g i n of the,. . .. 8!- 85 ---------,The,. .80- 165 Fire-clay, Definition of,.. . .. 35, 16!1 Fitzpatrick, Analysis and Description of Clay from the Vicinity of,.135- 1B6 -----, Clay Exposures in Gullies Hancock County, Clay Deposits in, . .. t. 148 Harris, Peter, The Brick-works of,. 105 Hatton, Dr., Cited. 157 Haworth, E., Cited. 123 Hofman and Demond, Cited .. .58, 76, 77- 78 Huckabee, J. W., ..... 111 near, . . . . . .134-13~, 137 Floyd's Creek, Clays along,. 150 Fort Valley Plateau, The,.. . .97- ~8 Inglett, Mary, The Clay Property of, .... 157-158 Fusibility of Clays, Description of the Elec- Irwinton. . ..... 127 tric Furnace t:sed for Testing,.. . .66- 67 , Description of the Oxy- J Hydrogen Furnace James, G. W., Potomac Clay on the Estate t:sed for Testing the,... 67 of, Described. . . . . . 110 --------, Indirect Method of ---, Mrs. Sally, Potomac Clays on the es- Testing.the,. . .. 74- 78 tate of, Described. 110 ---------,New Experiments on Jefferson County, Potomac Clay in,.. 150 the,... . .. 66- 74 Jeffersonville. 127 --------, llse of the Electric Fur- ------Road, Occurrence of Fossilif- nace in Testing the, 6B- 73 erous Tertiary Strata ---------, llse of the Oxy-Hydro- N