UNIVERSITY OF CALIFORNIA EARTH SCIENCES LIBRARY LIBRARY =1 UNIVERSITY OF CALIFORNIA GIFT OF" Class Ul E 5C LI GEOLOGICAL SURVEY OF ALABAMA, EUGENE ALLEN SMITH, Ph. D., State Geologist. BULLETIN No. 6. PRELIMINARY REPORT ON THE CLAYS OF ALABAMA, BY HEINRICH RIES, F>ti. D. THE VANCE PRINTING CO., STATE PRINTERS AND BINDERS, JACKSONVILLE, FLA. 1900. To His Excellency, JOSEPH F. JOHNSTON, Governor of Alabama. DEAR SIR : — I have the honor to submit herewith, as part of my biennial report, 1898-9, a report upon the clays of Alabama by Dr. Heinrich Ries. While the investigations of Dr. Ries here recorded have been confined to the northern half of the State, and mainly to one or two formations, they yet embrace the most important and most accessible of our clay deposits. The kaolins of the granite re- gion lie at a distance from railroad lines, and the discussion of these and of the clays of the more recent formations, in the lower half of the State, will be taken up in a second bulletin. The present report shows that our clay resources include every variety, ranging from the best of china clays downward, and there seems to be no good reason why all these materials should not be turned into the manufactured products, chinaware, stoneware, fire brick, ornamental brick, paving brick, tiles, drain pipes, etc., within our own borders and upon our own ground. Very Respectfully, EUGENE A. SMITH. University of Alabama, March 15, 1900. TABLE OR CONTENTS. Page. Letter of Transmittal. Preface 1 I. GENERAL DISCUSSION OF CLAYS, BY HEINRICH RIES, PH. D 3 Origin of Clay 3 Geological Structure and Distribution of Clay Deposits 6 Residual Clays 6 Sedimentary Clays 7 Distribution 8 Properties of Clays 8 Chemical Properties 9 Alkalies in Clays 11 Soluble Alkaline Compounds 11 Insoluble Alkaline Compounds '. 12 Iron Compounds in Clays 13 Lime in Clays : 16 Magnesia in Clays 19 Silica in Clays 20 Titanic Acid in Clays 21 Organic Matter in Clays 22 Water in Clays 22 Moisture 23 Combined Water 24 Physical Properties of Clays 24 Plasticity 25 Tensile strength 26 Shrinkage 26 Fusibility of Clays 29 The Thermo-Electric Pyrometer 31 Segar Pyramids 32 Chemical Effects of Heating 38 Slaking 38 Absorption 39 Color of Unburned Clays 39 Mineralogy of Clays 40 Kaolinite 40 Quartz 41 Calcite 42 Gypsum 42 Mica 43 Iron Oxide 43 vi Page. Pyrite 44 Dolomite 44 Methods employed in Making Clay Analyses 45 Rational Analysis of Clay 60 Classification of Clays 57 Mining and Preparation of Clays 59 Prospecting for Clays 59 Mining of Clays 60 Mining of Kaolin 61 Washing of Kaolin 62 II. GEOLOGICAL RELATIONS OF THE CLAYS OF ALABAMA, BY EUGENE A. SMITH, PH. D 69 Archaean and Algonkian , 70 Cambrian and Silurian Formations 73 Subcarboniferous Formation 77 Coal Measures 80 Cretaceous Formation 81 Russell and Macon Counties '. 87 Elmore and Autauga Counties 88 Bibb County 90 Tuscaloosa County 92 Pickens County 97 Lamar County 98 Fayette County 101 Marion County 104 Franklin County 107 Colbert County 109 Lauderdale County Ill Tertiary 112 III. PRELIMINARY REPORT ON THE PHYSICAL AND CHEMICAL PROPERTIES OF THE CLAYS OF ALABAMA, BY HEINRICH RIES, PH. D 114 China Clays 115 Rock Run, Cherokee County 118 Gadsden, Etowah County 119 Kymulga, Talladega County 121 Eureka Mine, DeKalb County 122 « " " « 123 Fort Payne 125 Chalk Bluff, Marion County 126 " « " « ; 127 Near Chalk Bluff, Marion County 127 Pearce's Mill, Marion County 128 Pegram, Colbert County 129 Fire Clays 130 Peaceburg, Calhoun County 134 Oxanna, " • " 135 vii Pa*e. Rock Run, Cherokee County (Clays) 136 11 " " " (Bauxites) 142 Valley Head, DeKalb County 146 " " " " 148 Fort Payne " " 149 Bibbville, Bibb County 150 Woodstock " " 151 Hull's Station, Tuscaloosa County 152 J. C. Bean, '• '• 153 Pearce's Mill, Marion County 155 11 " 156 Pegram, Colbert County 157 FlintClay, " (< 158 Pottery or Stoneware Clays 159 White, Blount County 160 Rock Run, Cherokee County 161 Chalk Bluff, Elmore County 162 « « « «« 162 Edgewood, '« " 163 " " " 165 Coosada, " " 165 Cribb's Pottery, Tuscaloosa County. 166 J. C. Bean, " " 168 " « " 169 Roberts' Mill, Pickens County 170 Bedford, Lamar County 172 Fernbank, " " 173 W. Doty, Fayette County 174 « « 175 Shirley's Mill," " 176 H. Higgins, " " 178 S. E. of Hamilton, Marion County 179 Th. Rollins, Franklin County 180 Pegram, Colbert County 180 Brick Clays 181 Brick Shales, Birmingham, Jefferson County 184 Paving Brick Shale, Coaldale, " " 186 Pearce's Mill, Marion County 186 Ten-Mile Cut, Tuscaloosa County 187 Oxford, Calhoun County (Dixie Pottery) 188 Shirley's Mill, Fayette County 189 Chalk Bluff, Elmore County 190 Woodstock, Bibb County 191 Birmingham, Jefierson County 192 Argo, " " 193 Miscellaneous Clavs 193 W. D. Bagwell, Fayette County ..' 194 viii Pa«e. Bexar, Marion Couuty 194 " " " 195 « " " 196 Glen Allen, Marion County 197 W. J. Beckwith, Colbert County.. 198 Utilization of Clay for Portland Cement 199 PREFACE, Clay is one of the most abundant materials found in the earth's crust, and occurring as it does in every country, in almost every geological formation from nearly the oldest to the youngest, and frequently in positions easy of access, it is not to be wondered at that these conditions, aided by the peculiar properties which it possesses, have caused this material to be- come one of the most useful and valuable products of the earth. The value of clay is still more readily understood when the statistics of Hs production are known. Thus in 1897, the total value of clay products made in the United States alone was $60,911,641.00, distributed as follows : Common brick $ 26,353,904 Pressed brick 3,931,336 Vitrified paving brick 3,582,037 Ornamental brick 685,048 Fire brick 4,094,704 Drain tile 2,623,305 Sewer pipe 4,C69,534 Terra cotta 1,701,422 Fire proofing 1,979,259 Tile other than drain 1,026,398 Miscellaneous 1,413,835 Pottery 9,450,859 Up to the present time the rank of Alabama as a clay producing state has not been very high, owing largely to the lack of information concerning its clay resources, and in the following report an endeavor has been made to furnish as much information as possible concerning the characters of many of the Alabama clays. HEINRICH KIES. March 1, 1900. I • GENERAL DISCUSSION OF CLAYS, BY HEINRICH RIES. ORIGIN OF CLAY. Clay is to be met almost every where, and while it varies in form, color and other physicial properties, nevertheless it always forms a pasty or plastic mass when mixed with water, by virtue of which it may be molded into any shape, which it retains when dried; furthermore when exposed to a high temperature it hardens to a rock like mass. These two properties, the plasticity and the hardening when burnt are what make clay of such inestimable value tio man. Pure clay or kaolin is composed entirely of the min- eral kaolinite, which is a hydrated silicate of alumina. It rarely happens, however, that clay is perfectly pure, for owing to the nature of its formation from another rock as will be explained later, it is very apt to have other minerals mixed in with it. These foreign min- erals may sometimes be present in such quantities as to completely mask the character of the kaolinite. We can therefore define clay as a mixture Of kaolin- ite with more or less quartz and other mineral' frag- • ments, especially feldspar and mica, the whole posses- si ng plasticity when mixed with water, and becoming hard when burned. The so called flint clays form an exception to the above, for while they often approach pure kaolin in composition, still they are almost devoid of plasticity when ground and mixed with water.' Kaolinite is a secondary mineral resulting from the decomposition of 'feldspar. The feldspars are a group of silicate minerals of Bather complex composition, 4 GENERAL DISCUSSION OF CLAYS. with orthoclase, the potash feldspar, serving as the type of the group, as well as being the commonest species. Under the influence of chemical action, which may be the result of weathering or in some cases probably of acid vapors ascendning from the interior of the earth, the feldspar becomes decomposed, and the result of this is that the potash of the feldspar is removed partly in the form of solube carbonate, or perhaps silicate, or even fluoride, while the alumina and silica remain and unite with water to form the hydrated silicate of alumina, kaolinite, whose composition is expressed by the formula A12 03, 2S102, 2H20., or in the proportion of silica, 47.30 per cent.; alumina, 39.80 per cent. ; water 13.90 per cent. The change can be illustrated still better by the fol- lowing in which the first column indicates the com- position of the feldspar, the second the amount of water taken up in the process of decomposition, the third, the amount, of matter removed in solution, and the fourth the relative amounts of the three ingredi- ents of kaolinite. Feldspar. Added. Dissolved out. Kaolinite. Alumina 18.3 0.0 18.3 Silica 64.8 .... 41.8 23.0 Potash 16.9 .... 1«.9 Water 6.4 .... 6.4 Many clays approach quite closely to kaolinite in their composition, and in some the percentage of alumina even exceeds the theoretic amount, by one or two per cent., and is evidently not due to errors of an- alysis. It has been suggested by some that this may be due to the presence of a certain amount of pholdrite, the amorphous variety of kaolin,* and while this is pos- sible the same composition might be shown by a cer- tain amount of bauxite or alumina hydrate mixed in wit'h the clay. Wheeler, Clays of Missouri, Missouri Geological Survey, XI. ORIGIN OF CLAYS. 5 None of the Alabama clays thus far analyzed indic- ate this exceptional composition. Knowing the mode of origin of kaolinite it will at once be seen that the purity of the kaolin depends on the nature of the parent rock. Feldspar often forms large veins of considerable purity, and nearly free from other associated minerals, and its decomposition in such cases would give rise to deposits of pure or nearly pure kaolin. In point of fact the purest clays known have with few exceptions been formed in this manner. More frequently quartz and mica are com- mon accessory minerals, and remain intermixed with the kaolinite, both of them being more resistent to weathering than the feldspar. When these or other minerals occtir in the kaolin they have to be separated from it as much as possible by washing. Clays, which occur at or close to the locality in which they have been formed, are called "residual clays". They represent some of the purest types of clay known as well as the most impure. The upland region of the Southern States is underlain by a great area of feldspathic, granitic and gneissic rocks which have decomposed to a ferruginous clay of residual nature, and one that is used extensively in the South for the manufacture of common brick. In the general wearing down of .the land surface which is continually taking place the particles of residual clay are washed down into the lakes and oceans and deposited there as sediments, thus giving rise to what are known as sedimentary clays. They are usually far more plastic than the residual clays,, especially the purer ones. From the nature of their formation, we should sel- dom look for kaolins of sedimentary origin, and when they do occur they have probably been derived from large areas of very feldspathic rock or possibly from limestones which had an appreciable percentage of silicate of alumina in their composition, in which case the lime carborate would be carried off in solution, and the clay components of the rock be left behind as an insoluble residue. It! is seldom that sedimentary 6 GENERAL DISCUSSION OF CLAY. clays exhibit such reniarkale purity as those from Chalk Bluff, Alabama, or the plastic ball clays of Florida. The clays of the Cretaceous and Tertiary forma- tions, which underlie the Coastal Plain, as well as the Palaeozoic shales found in Alabama, are all of sed;- nientary origin. GEOLOGICAL STRUCTURE AXD DISTRIBU- TION OF CLAY DEPOSITS. BESIDUAL CLAYS. The mode of origin of these has already been ex- plained. They may occur either in the form of a broad mantle overlying the bed rock and showing a variablt thickness as well as extent, or they may occupy the position of a vein cutting across the strike of the other rocks, or extending at times with the bedding or lami- nation of them. Residual clays are commonly made up of a mixture of angular grains which are chiefly undecomposed mineral matter, and clay particles which are mostly of sufficient fineness to remain suspended in water for an almost indefinite period. There is also generally a gradual transition from the fully formed clay at the surface to the f^esh rock beloAv, whose decomposition has given rise to the plastic mass above. The depth below the surface at which the unaltered rock is encountered may be as little as three to four feet, while in some regions where the surface 'has been little eroded, and decomposition has been active, the thickness of the residual clay may exceed one hundred feet. The structure of the parent rock such as stratifica- tion or lamination is at times often noticeable in the lower portion of the residual deposits, and in some cases it may even be preserved right up to the surface. Residual deposits of the vein type result commonly from the decomposition of veins of granite or feldspar. They vary in width, from a few inches to several hun- STRUCTURE AND DISTRIBUTION OF CLAY DEPOSITS. 1 dred feet, and their vertical extent depends in most cases on the depth to which the weathering action has progressed. Veins of kaolin seldom show great length, and when followed along the surface not uncommonly pinch out in both directions. They are often separated more or less sharply from the country rock, and this distinct line of demarkation is preserved even when the wall rock itself is decomposed. They- further- more frequently branch and at times contain lenses of quartz, which resist the weathering agencies and stand out in bold relief on the surface. It rarely pays to work a vein under six feet in width. Deposits of kaolin of the type just described should not be confused with sedimentary deposits of white clay, which are usually of a much greater extent than the vein formation. SEDIMENTARY CLAYS. These occur in the form of beds, which are either close to the* surface or inter stratified with other de- posHs which have been accumulated in water, such as sandstone or limestone. They are not unfrequently interbedded with coal deposits and many a coal seam has a fire clay floor. Sedimentary clays are, as a rule more homeogeneous than residual ones, and contain probably a greater portion of fine particles. They are also more plastic, and frequently contain much dis- seminated organic matter. Furthermore, they do not pass gradually into the underlying rock as residual clays do, and indeed bear no relation, in a genetic sense, to the rocks upon which they rest. When sedimentary clays become compressed by the weight of overlying sediments, they assume the character of hard or consolidated rock, and are known as shale. Shales therefore simply represent the finest clay sediment which has bcome consolidated. On grinding to a powder and mixing with water, shales become just as plastic as other clays. By mentamorphism, (that is heat and pressure developed 8 GENERAL DISCUSSION OF CLAYS. by mountain making processes) taking place in the crust of the earth, a shale may lose its chemically com- bined water, develop a cleavage, and become converted into slate. It is then no longer possible to develop any plasticity in the material. It is not to be understood that all sedimentary clays are of a homogeneous structure throughout. Some beds may exhibit a wonderful similarity of composi- tion throughout extended areas, while again theru may be a wide variation in the character of any bed within narrow limits. Apart from this variation laterally, there may also be a vertical one ;n cases where the de- posit is made up of a number of beds, one over the oth- er, each showing distinctive characters. With such oc- currences it is possible to obtain several different grades of clay from the same pit. Such conditions are apt to be the rule rather than the exception. A not uncommon phenomon in many of the coastal plain formations is the occurrence of large lenses 'of clay, free from grit surrounded by beds of sandy clay or even sand. DISTRIBUTION. Clays and shales occur in practically every geologi- cal formation with the exception of the oldest. Most of those which are older t'han the Creataceous are 'hard and shale — like in their nature, while those of the Cretaceous and Tertiary on the other hand are usually soft and plastic, but deposits of Creataceous and also Tertiary shales are known. The geological age of a clay or shale is no indication of its quality, and it is only of use at times for a means of comparison between two beds situated near each other, but even here it is not altogether a safe guide. The geological relations of the clays of Alabama are treated somewhat more in detail below in a separ- ate chapter. PROPERTIES OF CLAYS. These fall into two classes-, i. e. (1) Chemical and (2) Physical. Two clays may correspond in their CHEMICAL PROPERTIES OF CLAYS. 9 widely in their physical characters, and therefore act entirely opposite when used for the manufacture of clay products. Pure clay or kaolin would be composed entirely of kaolinite, the hydrated cilicate of alumina. These two terms are often confounded and it is well to em- pahasize the fact that kaolinite refers to the mineral species, while the term kaolin is applied ito the mass. Pure kaolin has net thus far been found, although deposits containing as much as 98 per cent, of it are known, and the othe" two per cent, consists of foreign matter. The kaolin therefore contains a variable amount of mineral 'mpurities mixed in with the kao- linite or the clay substance, as it is some times called, and these impurities may affect both the chemical and the physical properties to a variable extent, depend- ing upon the quantity and the kind of them present. The clay substance is always present but in a variable amount, and it stands in no direct relation to the plasticity, except in so far that the latter is lost when the combined water is driven off. The amount of clay substance in clays ranges from 5 or 10 per cent, to 98.5 per cent. The chief impurities in kaolin* are quartz, feldspar and mica, but in other clays the number of mineral species present may indeed be large. CHEMICAL PROPERTIES. The chemical composition of a clay directly influ- ences its fusibility, and the color to which it burns. The compounds which may be found in clay are silica, alumina, iron oxide, lime, magnesia, potash, soda, sulphuric acid, phosphoric acid, manganese oxide and organic matter. Compounds of chromium and vanadium may also be present at times in small amounts. All of these substances are not present in every clay, but most of them are. Pure clay would contain silica, alumina and com- bined water, but the purest clay known commonly contain at least traces of iron oxide, lime and alkalies. 10 GENERAL DISCUSSION OF CLAYS. Alumina, organic matter and water are practically the only non-volatile constituents, which do not exert a fluxing action on the clay in burning, and the inten- sity of this fluxing depends partly on the amount of fluxes, and partly on the temperature at which the clay is burned. It is the custom to divide the impurities of clay into t'hose wlr'ch are fluxing, and those which are non-flux- ing. Pure clay is very refractory. The kaolinite com- posing it contains two molecules of silica and one molecule of alumina. A higher percentage of silica tends to increase the fusibility up to a certain point, provided it is in a finely divided condition, above this point the refractoriness of the clay increases steadily with the addition of silica. Other substances are far more powerful fluxes than the silica however, and these fluxes contain not only elements but also definite chemical compounds or mineral species. The influence of fluxes increases not only with the amount present but also with the state of division, they being more active, the more finely they are divid- ed. If the fluxing material is present in large grains, these will only exert a fluxing action on their upper, surface, while the single grains alone will for a while act more like quartz grains i. e. as diluents of the shi inkage. The minerals which may be present and serve as fusible impurities are commonly mica, feld- spar, hornblende, pyroxene, garnet, quartz, calcite, gypsum, iron oxide and manganese, and the elements contained in these constituting the active fluxing agents are alkalies, iron oxide, lime and magnesia. Opinions differ somewhat in regard to the order of their relative effectiveness, but it is probably given above, the alkalies being the strongest. The amount and kind of fluxes which it is desirable for a clay to contain depends on the use to which it is to be put. If a vitrified ware is desired then the fluxes should be present in appreciable amount, say 10 to20per cent, depending upon the relativestrength CHEMICAL PROPERTIES OF CLAYS. 11 of the fiuxmg- impurity. Refractory clays, on the other hand, should contain a low amount of fustt^e substances. Porcelain clays might have as high a per- centage of fluxes as 5 or 6 per cent., provided they did not exert a coloring action on t'he clay. ALKALIES IN CLAYS. / The alkalies usually contained in clays are potash, soda and ammonia. Ammonia is a very common constituent of moist clay and is absorbed by the latter with great avidity; indeed it is largely responsible for the characteristic oder of clay.* If the ammonia remained in the clay, it would act as a strong flux, but its volatile nature renders it harmless, for it passes off as a vapour at a temper- ature considerably below dull redness, and in fact may even volitilize with the moisture of the clay during the early stages of burning. Potash and soda on the other 'hand, which volati- lize only at a high temperature, are present in almost every clay from the smallest amount up to 9 or 10 per cent, and of these potash is by far the commoner of the two. Their variable percentage may be caused by the presence of more or less undecomposed feldspar, of which orthoclase, the common species, has nearly 17 per cent, of potash while the other feldspars contain varying amounts of soda. These alkalies may be present in the clay in the form of either soluble or insoluble compounds, the latter being represented by feldspar, mica, or ot'her minerals, while the soluble ones are usually the result of their decomposition. Soluble alkaline compounds may be found in almost any clay, but they are rarely present in large amounts, ard1 their chief importance lies in the fact that they are often responsible for the formation of an efflor- escence or whHe coating on the surface of the ware, they having become concentrated on the surface by the *P. Senft, Die Thon Substanzen, p. 29. 12 GENERAL DISCUSSION OF CLAYS. evaporation of the moisture of the clay. They may be rendered insoluble by the addition of chemicals to the clay. In addition to its unsightliness the efflores- cence may interfere with the adhesion of a glaze ap- plied to the surface of the ware. Soluble alkaline sulphates are powerful fluxes and they also cause blistering of the ware, if the clay is heated sufficiently high to decompose the compound and permit the escape of sulphuric acid gases. In some clays containing sulphate of iron, this com- pound may be decomposed by chemical reaction tak- ing place in the clay; the sulphuric acid, which is thus set free, is apt to attack the alumina of the clay substance and if potash, soda, or ammonia 's present there is formed an alum of potash, soda or ammonia, which can often be detected by the taste which ic im- parts to the clay. Insoluble alkaline compounds. Feldspar and mica which are the commonest of rock forming minerals are the two important sources of insoluble alkaline salts in the clay. The feldspars are complex silicates of alumina and potash, or alumina, lime and soda. Orthoclase is the only species furnishing potash and contains about 17 per cent, of it while the lime-soda feldspars have from 4 to 14 per cent, of soda depending on the species. Orthoclase is the common feldspar, and next to it come albite end oligoclase with 12 and 14 per cent, of soda respectively. The micas are complex silicates of alumina with either lime or magnesia or potash. Muscovite, the common species, contains nearly 12 per cent, of pot- ash, and may at times also contain soda, While the potash feldspar fuses completely at about 2300° Fahr., the potash mica alone is very refractory and unaf- fected by a temperature of 2550° F^hr., and though it probably serves as a flux, it is not definitely known at just what temperature its action begins. The alkaline silicates on account of t'heir fluxing properties are frequently at an advantage, especially if in the form of feldspar, as they serve in burning to CHEMICAL PROPERTIES OF CLAYS. . 13 bring the particles of the clay together into the dense hard body, and also permit of the ware being burned at a lower temperature. If present in kaolins to the extent of several per cent, it is no detriment, provided no iron is present; an excess of feldspar, however, when added to a white burning clay will tend to pro duce a creamy tint. In the manufacture of porcelain, white earthen ware, encaustic tiles and other products made from kaolins or white burning clays, and having a white body, which is impervious, or nearly so, the alkalies for the fluxing of this body are added in the form of feldspar. Much feldspar is mined in this country for potters use, but all of H is the ortholase or potash feldspar. IRON COMPOUNDS IN CLAYS. Iron is not simply a fluxing impurity, but it is also the great coloring agent of clays in either their burned or unburned condition, and furthermore when in the form of the hydrated oxide or limonite it may serve to increase the absorbtive power of clay. * The compounds in which iron may exist in the clays are as follows : Oxides : — limonite, hematite, magne- tite, ilmenite. Silicates: — mica, hornblende, garnet, etc. Sulphides : — pyrite and marcasite. Sulphate : — melanterite. Carbonate : — siderite. The iron oxides, limonite and hematite, are present in all clays, and may be introduced by percolating waters or be set free by the decomposition of any of the iron-bearing silicates which the clay may contain. Not infrequently they are distributed through the clay in a very finely divided condition, or may form a thin film around the other mineral grains. Limonite tends to color the clay (unburned) brown or yellow, while 'hematite imparts a red color to it, and carbon- ate of iron may give gray tints. The more sandy the clay the less the amount of the * A. E. Smith, Alabama Geological Survey, Agricultural Report, p. 45. 14 GENERAL DISCUSSION OF CLAYS. limoiiite required to produce any given intensity of color. Mica is found in most clays, and hornblende and garnet are probably wanting in few, while the pyrite is often present in many clays, especially in stoneware and fire clays, its yellow, glittering, metallic particles being easily recognizable. When large, the lumps of pyrite can be extracted by hand-picking, but if very small, they can only be separated by washing. Un- der weathering influences the pyrite changes to sul- phate of iron. In all of the iron-bearing minerals rthe iron is present in either the ferrous or the ferric stage of oxidization, and the fusibility of the clay is in- fluenced somewhat by this fact, for ferrous com- pounds are more easily fusible than ferric ones. In the burning of the clay the ferrous salt will be con- verted into the ferric state, provided the action of the fire is oxidizing. But if it is reducing the clay will fuse at a lower temperature. The action of weathering agent in nature is often sufficient to oxidize the iron in clays so that more ferric than ferrous iron will' be found in most of them. This change is often noticeable in many clay banks where the upper, and at times more porous layers, are colored red or yellow, while the lower layers cire blue or bluish gray. It should be noticed, however, that a gray color may be produced by the presencce of organic matter, and the same material present in a dense clay, to which the air can not get access, may serve to retard the oxi- dation of the iron. Whenever iron exists in clay in combination Avith s;lica it is present probably as a complex silicate, for pure ferric silicate u very rare in nature. Ferric hydrate increases the absorbing power of clay for both gases and liquids, but it as well as the carbonate change to the oxide in burning. The general tendency in burning is to convert the iron compounds into ferric oxides, provided a certain temperature, depending on the fusibility of the clay, is not exceeded, for in every clay the iron seems to re- CHEMICAL PROPERTIES OF CLAYS. 15 turn to the ferrous condition as the point of vitrifica- tion is approached. This change is accompanied by a liberation of oxygen, which is responsible for the active swelling and blistering of the clay, which takes place as the point of viscosity is approached. If treated to an oxidizing fire, the presence of fer- rous salts in clay may not be considered, provided the heat is raised high enough to oxidize them, but the rapidity wHh which the temperature is raised is im- portant, for when the heat is increased rapidly the outer portion of the clay tends to shrink and become dense before the air has had time to enter and oxidize the iron in the center of the clay body,- the latter re- maining in ferrous state. This is the cause of black cores sometimes seen in bricks whose exterior is red* Unburned clay may be yellow, blue, brown, red or gray in color, depending on the relative amount of ferrous and ferric salts present, for iron is the one ele- ment above all others which by itslf colors clays. The same variety of shades and colors may be pro- duced in burning. Ferrous oxide alone produces a green color when burned while ferric oxide alone may give red or purple, and mixtures of the two may pro- duce yellow, cherry red1, violet, blue and black.* Segar found that combinations of ferric oxidie with silica had a red or yellow color§ wlrle similar com- pounds of the ferrous salts showed blue or green. The color -to 'Which any given clay burns may also depend on the intensity of the firing. Thus with mod- erate burning the iron may color a clay yellow or yel- loAvish red, \vith harder firing this will pass into deep red, and on still more intense heating to blue or black, this latter color is to be seen on breaking open the arch brick in many kilns, but the surface of these same brick may also get black, due to ashes and cinders from the fire sticking to them. The amount of ferric oxide permissible or desirable depends on the use to which tlhe clay is to be put. *Keramik, p. 236. }$0tizbiatt, 1874. p. 10. 16 GENERAL DISCUSSION OF CLAYS. The clays which are used for making white ware should not contain over one per cent ferric oxide. And those with even three-quarters of one per cent, are apt to burn grayish at a high temperature, such as 2700 deg. Fahr. It is true that the reddish color- ation of a small percentage of iron would be neutral- ized if any excess of carbonate of lime were present, but in this case even we should not get a pure white tint, but a yellowish one. Brick clays should contain sufficient iron oxide to give a good red color to 'the ware when burned. The bleaching of the iron coloration by the presence of lime wUl be mentioned later, an excess of alumina also tends to exert a decolorizing action upon the iron contained in the clay. • ( LIME IN CLAYS. Lime is a most wide-spread constituent of clays, and occurs either in a finely divided state or else in the form of pebbles. An excess of lime in the clay in the former condition causes it to pass into marl, and in certain regions such clays are extremely abundant. Lme may occur in clays either as a constituent of silicate minerals such as feldspar ; in the form of car- bonate as exampled by calcite or dolomite; or thirdly it may be present as a sulphate, which is the mineral gypsum. The fi^st two classes of compounds include minerals which are primary constituents of the clay, but the third type, gypsum, is usually of secondary origin, be- ing the'result of chemical processes, wlrch took place in the clay mass. The condition of lime is important, for in one case, it may be desirable, and in another it may do injury. The presence of lime as a constituent of some silicate mineral is not infrequent, especially if the clay has been derived wholly or in part from crystalline rocks, such as gneisses and granites. The common feldspar, orthoclase, contains no lime, but the other species of feldspar do, and in addition there are other lime bear- CHEMICAL PROPERTIES OF CLAYS. 17 ing silicates which are apt to be met with in most of the impure clays. When present as a silicate, lime acts as a flux, and is less liable to exert a decolorizing action on the clay than carbonate of lime. Bleaching action is caused by the formation of a double silicate of iron and lime, when the clay reaches a temperature approaching vit- rification, and the color developed is either yellow, or yellowish green, according to the intensity of the firing. Carborate of lime is an abundant constituent of some clays, and its presence, if over three or four per cent, can usually be detected by the effervescence which is produce! when muriatic acid is poured on the clay. This compound of lime is far more injurious than the silicate, although, if present in the clay, in a finely divided condition, it may not only be harmless but even desirable, provided there is not an excess of it, for clays with as much as twenty to twenty-five per cent, of lime carbonate have been used for making common or even pressed brick and somtimes earthen- ware. It is well, however, to try and keep the amount lower than this if possible. Highly calcareous clays have often found a use in making of slip glazes. If the carbonate of lime is present in the form of pebbles, a most undesirable effect is produced, for it is well known that when heated to redness, the com- pound is broken up into oxide of lime and carbonic acid gas ; this oxide of lime, when cooled, absorbs mois- ture from the atmosphere and slakes, the result being a swelling of the material and a consequent splitting of the brick. Now if the clay be heated to a tempera- ture sufficenit to decompose the carbonate of lime, but not high enough to make it unite with any free silica present, the lime of course slakes on cooling. It is con- sequently imporatnt either to b,urn the clay sufficently or remove the lime pebbles from the clay by screening or by some other method before using. For a high grade ware, calcareous clays are seldom employed, but in the manufacture of brick and terra- 18 GENERAL DISCUSSION OF CLAYS. cotta, they are frequently utilized either because no others are available or to obtain a buff colored ware. Some soft body porcelains have an appreciable amount of lime, much of the Hungarian containing from five to fifteen per cent, of CaO.* The bone china made in England at the present day also contains lime and some white earthen ware manufacturers use lime instead of feldspar. Much buff ware is now made from semirefractory clays, which, on account of their low percentage of iron, burn to a creamy color. The one objection to highly calcaeous clays is that the points of incipient fusion and vitrification (see Fusibility of Clays) lie so close together that it is not safe to burn them hard without running the risk of fusing them. Experiments 'have shown however, that it is possible to separate these two points, by the addition of quartz and feldspar to the clay, of sand containing a large percentage of these two minerals. In addtion to lowering the fusibility of clay, lime also affects the fusion and absorptive power, thus Segar found §§ that limy or marly clays required us- ually only twenty to twenty-four of water to convert them from a dry condition to a workable mass, where- as other clays needed twenty -eight to thirty per cent, of water to accomplish the same result. In burning the calcareous clays have not only their combined water to lose, but also the carbonic acid gas, and con- sequently the bricks are more apt to be light and po- rous unless they can be burned to vitrification. The shrinkage of calcareous clays is also less than that of others, and it sometimes happens that this shrinkage i*> not only zero, but that the brick even swells. Many clays contain lime in the form of gypsum, the hydrated sulphate of lime. It generally results from the action, on carbonaie of lime, of sulphuric acid set free by the oxidation and leaching of pyrite in the clay. *Sprechsaal, 1896, p. 2. gHecht, Thonindustrie Zietung. % Thonindustrie Zietung, 1877, p. 131. CHEMICAL PROPERTIES OF CLAYS. 19 When in large amounts, gypsum discloses its presence by the formation of transparent crystals or crystallne masses, whose surface shows a pearly lustre; at ot'her times it forms as parallel fibres which fill cavities or cracks in the clay. Gypsum may prove to be a very injurious impurity even when in small amounts, es- pecially if the clay is not burned to vitrification. In the first place it serves as a fluxing impurity, secondly, ,it is dissociated at high temperatures, and the escape of the sulphuric acid causes blistering of the ware, and thirdly, although nearly insoluble in water, nevertheless small amount of it may be brought to the surface of the ware in solution by the evapora- tion of water and there left in the form of a white coat- ing. Kaolins commonly have very little lime, but in many common brick and stone ware clays, it frequently ranges from one to three per cent. MAGNESIA IN CLAYS. Magnesia is a constituent of many minerals, and yet it seldom occurs in large quantities, the amount in most of them rarely exceeding two per cent. It may occur, in the same classes of compound as lime i. e. silioates, such as mica, chlorite, hornblende and pyroxene; in carbonates, such as dolomite and magnesite; and in sulphates, such as epsom salts. The silicates are, no doubt, the most important source of magnesia, for mica, chlorite, and hornblende are all common constituents of the more impure clays. They are scaly minerals of complex composition and contain from 1 to 25 per cent, of magnesia, The mica is frequently to be noticed in the sandy seams of the clay, while the other portions of the deposit may be quite free from it. Hornblende and pyroxene are to be looked for mostly in clays derived from the dark colored igneous rocks, and indeed the two latter min- erals not only furnish magnesia, but by their decom- position furnish also iron oxide to the clay. Dolomite, the double carbonate of lime and mag- 20 GENERAL DISCUSSION OF CLAYS. nesia, may' be present in some clays derived from mag- nesian limestone,, while the sulphate of magnesia or epsom salts when present, may aid in the formation of a white coating on the surface of the ware; its pre- sence can sometimes be detected by the bitter taste which it imparts rto the clay. The effects of magnesia in clays are considered to be the same as those produced by lime. SILICA IN CLAYS. Three types of silica may be recognized in clay, i. e. 1st. Quartz. 2nd. That which is combined with alumina and water in kaolinite. 3rd. That which is combined with one or more bases, forming silicate minerals, such as feldspar, mica, etc. In chemical analysis the first and third are some- times grouped together under t'he name of sand, or at times erroneously spoken of as free silica. The sand is practically insoluble in sulphuric acid and caustic soda and this fact is utilized in the ration- al analysis of clay. Few clays, so far as known, are free from quartz, but it is present in variable amounts in different ones. A minimum of .2 of one per cent, has been recorded from New Jersey* while the average in the Wood- bridge fire clays is five per cent. In the Missouri flint clays, a minimum of .5 of one per cent., is recorded, while the sand percentage is 20 to 43 per cent, in the St. Louis fire clays, and 20 to 50 per cent, in the Loess clays, § 27 samples of Alabama clays contained from 5 to 50 per cent, of insoluble residue. 70 North Carolina clays 'had from 15.75 per cent, to 70.43 per cent, of insoluble residue. In European clays similar variations are observ- able. The most important effect of silica or sand is *G. H. Cook, Cllays of New Jersey, 1878, p. 273. § Wheeler, Missouri Geological Survey, XI, page 84. CHEMICAL PROPERTIES OF CLAYS. 21 that as it increases the plasticity, tensile strength, and air shrinkage tend to decrease. In fact silica es- pecially if present abundantly in large grains, may cause an expansion of the clay in burning. Quartz serves as a flux at very high temperatures, but at lower ones it tends to increase the refractori- ness of the clay, and this property is governed some what by the size of the quartz grains and the amount of fluxing material which will fuse at lower tempera- tures. Sand acts as a diluent of the shrinkage in air drying and also in burning up to a certain point depending upon the fusiblity of the constituent grain. In the burning of low grade clay, the quartz grains tend to act as a skeleton and preserve the form of the mass, while the fluxing impurity by their fusion bind the whole together. TITANIC ACID IN CLAYS. Titanium generally occurs in clays in the form of the mineral rutile (titanic oxide). It has always been looked upon as a rare element and a non-detri- mental impurity, but the idea of its rarity has pro- bably resulted from the fact that it is not commonly determined or looked for in the ordinary quantitative analysis. Its effect on the fusibility of clay has never been thoroughly understood, although it has seemed probable that its action was somewhat analogous to that of silica. The experiments of Seger have indicated that when a hundred parts of kaolin and 6.65 per cent, titanic oxide were heated to above melting point of wrought iron, the resulting mass was densely sintered, and showed a dark blue fracture. 13.3 per cent, added to a hundred parts of kaolin gave a deep blue enamel at the same temperature, while an equal amount of kaolin with the addition of 10 per cent, of silica burned to a snow white mass at the same temperature and did not fuse. From this it will be seen that the actions of titanium and silica at high temperatures are not exactly alike. 22 GENERAL DISCUSSION OF CLAYS. ORGANIC MATTER IN CLAYS. Organic matter affects not only the color of clay but also its plasticity, absorptive power and tensile strength. It is present in clays either in the form of finely divided pieces of plant tissue or larger fragments of stems or leaves, which settled in the clay during its deposition, and have since become wholly or partly converted into lignite. All surface clays contain plant roots, but these exert little effect other than to aid the percolation of surface waters. Clays colored by organic matter and containing no iron, burn white, as the plant tissue burns off at bright redness; if such a clay, however be heated too quickly, the surface of it becomes dense before all of the organic matter has had opportunity to escape from the interior, and the latter remains dark colored. Organic matter may also mask the presence of iron so that the clay, instead of burning white, will burn red at a temperature of above that at which the or- ganic matter passes off, below that temperature the vegetable matter will tend to keep t'he iron reduced. The clay from Fernbank, Lamar County, Alabama, contains 6.40 per cent of ferric oxide, and 2 to 2-| per cent of organic matter, but in the raw material, the latter hides the former. Organic matter exercises an important influence on the plasticity, often increasing it to an enormous degree, it also tendst to elevate the tensile strength, the clay just mentioned showing 185 pounds per square inch, but high plasticity does not always indicate the presence of much organic mate- rial. In the weathering of clays organic matter by its slow oxidation, aids1 in breaking them up by the es- cape of the carbonic acid gas. WATER IN CLAYS. All clays contain two kinds of water : — 1st. Hygroscopic water or moisture ( mechanically absorbed ) . 2nd. Chemically combined water. CHEMICAL PROPERTIES OF CLAYS. 23 * The moisture in air dried clays may be as low as .5 per cent, and reach 30 to 40 per cent, in those freshly taken from the bank. In the air dried specimens in the Alabama samples tested, it varied from .12 per cent, to 3.4 per cent. In air drying most of the moisture is expelled, and this is accompanied by a shrinkage of the clay, which, in the case of the Alabama samples, was usually from 2 to 7 per cent., but in one case it reached 14 per cent. The air-shrinkage of the clay ceases however before all the moisture passes off, the reason for this being that the shrinkage ceases when the clay particles have come in contact with each other, but there may still remain spaces between them which hold the water by capillarity, and the brick will contiue to lose weight but not in size, until all of this water has been driven off. la practice it is this latter portion of the moisture that evaporates during the first period of the burning known as water smoking. The air shrinkage of a clay varies with the nature of the material. Sandy clays usually show the least shrinkage, and of this kind the coarse grained ones diminish the least in size, while highly plastic clays usually show a high contraction in volume. The amount of water, which a dry clay needs to develop its maxium plasticity is a variable quantity. Plastic clays absorb a large amount, but a lean clay and fine grained one may do the same. As a very gen- eral rule it may be stated that lean clays absorb from twelve to twenty per cent, of water, while fat 'clays anywhere from twenty to fifty per cent., and the more water a clay absorbs the more it has to part wit'h in drying and the greater will be its shrinkage. If green ware is dried too rapidly it may split, not only from differential shrinkage between the exterior and the interior surface, but the rapid escape of steam may, in the first stage of the burning, tend to burst the ware. Highly aluminous clays do not always absorb the most water, nor are they the most plastic, and some 24 GENERAL DISCUSSION OF CLAYS. clays low in alumina and high in organic matter are not only 'highly plastic but also absorb a large quanti- ty of water. In the manufacture of clay products the moisture is partly expelled by exposing the ware to the sun or putting it in heated tunnels or rooms, while the last traces of moisture a~e driven off in the early stages of burning. Moisture may play another important and injurious role in clay working by its tendency to dissolve the sol- uble salts in the clay and bring them to the surface in drying, where they are left in the form of a white coating. It may also permit the acids which are con- tained in the fire gases; of the kiln, to act on the min- eral ingredients of the clay, and thus form soluble compounds, especially clorides and sulphates. Combined water is present in every clay. In pure kaolin there is nearly 14 per cent, of it, in other clays the percentage depends on the amount of clay base and the presence of other hydra ted minerals, such as limonite. Combined water is driven off at a low red heat, and when this occurs the clay suffers an additional shrink- age. It is a curious fact that although the combined water does not determine the degree of plasitlcity of the clay, nevertheless when once driven off the clay can no longer be rendered plastic. The greater the amount of combined water, the greater the shrinkage, and in the burning the Alabama clays it varied from 2-J to 12 per cent. PHYSICAL PROPERTIES OF CLAYS. These are fully as important as chemical ones, if not more so, plasticity for instance being a character of enormous value. The physical characters which are of the most im- portance from the practical standpoint, are plasticity, fusibility, shrinkage, tensile strength, slaking, absorp- tion and density. PHYSICAL PROPERTIES OF CLAYS. 25 PLASTICITY. This is the property by virtue of which a clay can be moulded into any desired form when wet, which shape is retained by it when dry. Just what the cause of plasticity is still remains to be definitely proven, although several theories, some of them very reasonable ones, have been advanced. It is an exceedingly variable property and we can find all stages in the transition from the highly plastic fclay to the slightly coherent sand. Clays, which posses little plasticity are said to be lean, while 'highly plastic ones are called fat. Pure or nearly pure kaolins are nearly always lean, while clays low in kaolinite may be highly plastic, thus for instance the clay from Chalk Bluff, and the stone- ware from Prattville, containing respectively 36.50 and 26.98 per cent, of alumina are both lean, while the clays from Fayette Court House and Fernbank con- taining only 19.68 and 13 per cent, of alumina respec- tively are both highly plastic. Cook has shown that the plasticity of some kaolins may be increased by grinding them, the result! being to tear apart the little particles of clay which were bunched or clustered together and thus permit a great- er mobility of the grains or scales of clay over each other. Mica decreases the plasticitv of clay, and if, in a finely divided condition, tends to make it flaky when wet. Plasticity, whatever its cause, is an important pro- perty from a commercial standpoint and highly inter- esting from a scientific one. The amount of water re- quired to develop the maximum plasticity varies. If too little is added the clay cracks in moulding and is stiff and hard to work ; if too much is mixed in with the clay it becomes very soft and retains its shape with difficulty. Lean clays usually require less water to produce a workable mass than plastic ones. The Alabama clays require from 25 to 30 per cent, of water to develop their maximum plasticity. 26 GENERAL DISCUSSION OF CLAYS. TENSILE STRENGTH. The tensile strength or the binding power of a clay often stands in relation to its plasticity, but not al- ways. It exerts an important effect in connection with the cracking of the ware in drying. The com- mon method of determining it is to form the plastic clay into briquettes of the same shape as t'hose used in the testing of cement. When air-dried they are tested in the regular cement testing machine, and their ten- sile strength per square inch is determined. Before breaking, the cross section of th.e briquette must be carefully measured, as the clay shrinks in drying and the tensile strength per square inch has to be calcu- lated from this sectional area. , The tensile strength of air-dried clays is extremely variable. In kaolins it is from 5 to 10 pounds per square inch ; in brick clays 60 to 75 pounds per square inch and even 100 pounds; in pottery clays from 150 to 175 pounds. Some very plastic clays show as much as 200 and 300 pounds per square inch, and a tensile strength of even 400 pounds has been recorded. The strongest Alabama clay were the highly plastic one from Chalk Bluff, which had a maximum tensile strength of 384 pounds per square inch, while the Choctaw County one showed only 5 pounds per square inch. The Alabama clays were all ground and passed through a thirty mesh sieve before testing. Very fine grained clays seem to be lacking in tensile strength as t'hey are in plasticity. SHRINKAGE. All clays undergo a shrinkage in drying and an ad- ditional shrinkage in burning, the first is known as air — , the second as fire-shrinkage. Some clays shrink most in drying, others most in burning, and conse- quently the amount is variable and depends on the amount of water absorbed, on the amount of lime in PHYSICAL PROPERTIES OF CLAYS. 27 the clay, the quantity of organic matter, the size of the grain, and the amount of combined water. The amount of .water absorbed, and the texture in- fluence the air-shrinkage which begins as soon as the water commences to evaporate from t'he clay. It has already been mentioned that a clay keeps on losing in weight after the shrinkage has ceased, and this fact is well shown by the following experiments on some Ala- bama samples. The clay was from property of J. C. Bean, Sec. 31, T. 20, R. 11 w. After moulding, the clay weighed 35.698 grams. At end of 24 hours the shrinkage was 11 J per cent, and the weight 30.891 •' At end of 48 hours, shrinkage 12 per cent., weight 29.588 " At end of 6 days, shrinkage 12 per cent., weight 29.460 u At end of 8 days, shrinkage 12 per cent., weight 29.140 " At end of 12 days, shrinkage 12 per cent., weight 29.093 " Throughout this period the clay was kept exposed to a temper- ture of 70° Fahr. The shrinkage is generally equal in all three direc- tions, and consequently only the linear shrinkage is given. The greater the shrinkage of a clay the more danger there is of its cracking and warping in burn- ing, and when there is any apprehension that this may occur, an attempt is made to prevent it by t'he addition of grog (burned clay) which diminishes the shrinkage. Coarse grain clays having larger pores permit the water to escape more rapidly, and hence can be dried more quickly than fine grained ones, from which the water can not very readily escape. If the drying of fine grained clays is hastened, the surface shrinkage is more rapid than that of the interior and cracking ensues. We might perhaps expect that on account of their greater porosity; the fine grained clays would absorb more water, and consequently shrink more in drying, but the Alabama clays do not always bear out this fact. The fire shrinkage generally commences when the 28 GENERAL DISCUSSION OF CLAYS. combined water begins to pass off, and it may be just as variable as the air shrinkage. In fine grained clays, as those from near Prattville, the shrinkage from buining was found to be comparatively uniform, while on the other hand moderately fine grained kaolin from Rock Kun shrank more rapidly as it ap- proached the temperature of vitrification. Sometimes the clay instead of shrinking during the burning appears to expand ; and this is especially the case with very quartzose ones, for the quartz has the property of expanding at 'high temperatures. This expansion of siliceous clays may sometimes be respon- sible for the presence of cracks in the burned ware. As the addition of quartz to diminish the shrinkage also tends to decrease the tensile strength of the clay, there will be a certain limit beyond which it must not proceed. Organic matter and combined water tend to in- crease the shrinkage in burning, but lime has the opo- site tenlency. Clays containing a large amount of feldspar will, in stead of showing a steady shrinkage up to the temper- ature of complete vitrification, often exhibit a tempo- rary'increase of volume when the fusing point of the feldspar is reached. The shrinkage of most clays in burning does --ot proceed regularly and steadily up to the temperature of vitrification, for some clays attain their maximum density at a comparatively low temperature, below that at which thev vitrify. Thus the plastic clay of J. C. Bean, near Tuscaloosa, attains its maximum shrinkage at cone 5, but does not vitrify until cone 27. Between the pointi at which the moisture seems to pass off and that at which the combined water begins to escape, the clay shrinks little or none at all, and PHYSICAL PROPERTIES OF CLAYS. 29 consequently the heat can be raised rapidly in this in- terval, but above and below these two points it must proceed slowly to prevent cracking or warping of the ware. FUSIBILITY OF CLAYS. It can be said in general, that other things being equal, the fusibility of a day will increase with the all the fuxing impurities do not act wit'h the same in- approximate statement however, for in the first place all the fluxing impurities do not act wit'h the same in- tensity, and of two clays containing the same amount and kind of fluxes, that one which has the finer grain will usually fuse at the lower temperature, in addition to this the condition of the fire, whether oxidizing or reducing, also exerts an effect. White mica tends to increase the refractoriness of a clay, and to exert very little fluxing action even at moderatly high temperatures. As a clay is gradually heated, it not only shrinks, but also begins to harden. At the temperature at which the combined water begins to pass off, the im- pure clays acquire such a degree of hardness that they can no longer be scratched1 by a knife ; but *n the case of purer clays, the temperature must be raised much higher to obtain this same degree of hardness. This condition is brought about by the clay particles be- ginning to soften under the action of the heat, in other words it represents the very first; stages of melting or incipient fusion, and in this condition the clay parti- cles stick to each other, and bind the whole together into a solid mass. In clays which have been burned to incipient fusion, th< particles are howWer still rec- ognizable. If the temperature be increased, a vari- able amount, depending upon the clay, the result is 30 GENERAL DISCUSSION OF CLAYS. that all of the particles become sufficently soft to per- mit their adjustment into a condition of greater com- pactness, leaving no interspaces, or in other words, the clay becomes impervious. This condition is spoken of as virtification, or complete sintering. The particles of the clay are no longer recognizable, and the maximum shrinkage has been reached. With a further elevation of the temperature the clay mass fusses completely, and becomes viscous or flows. We therefore can recognize three stages in the burn- ing of the clay, i. e., incipient fusion, vitrification and viscosity.* The points of incipient fusion and viscosity may be within 75 degrees Fahr. of each other as in calcareous clays, while in some fire clays they may be as much as 500 or 600 degrees apart, and furthermore the point of vitrification does not necessarily lie midway be- tween the two. Most clays show a difference of from 200 to 400 degrees Fah^. between the points just mentioned, and it can be easily understood the farther apart these two points, the safer will it be to burn the clay, for it is not always possible to control a kiln within a range of a few degrees of temperature, and therefore in burn- ing a mass of ware to vitrification if this point lies too near that of viscosity, there is danger of overstepping it and reaching the latter. The fusibility of a clay depends on : 1. The amount of fluxes. 2. Size of the grain of the refractory and the non- refractory constituents. 3. The condition of the fire, whether oxidizing or reducing. "These three terms have been suggested by H. A. Wheeler, Vitrified Paving Brick, 1895. PHYSICAL PROPER! IES OF CLAYS. 31 Attempts have been made to express the fusibiliy of clays nuniercally, and this number has been called the refractory quotient by Bishop* and the fusibility factor by Wheeler. § In both cases, the figure is obtained by using the non-fluxing elements of the clay for the numerator, and the fluxing impuri- ties as a denominator; and in the case of the second formula, the fineness of the grain was also taken into consideration. As this mode of expressing the fusi- bility has not come into general use, the reference is simply given here. On the other hand, it is customary to express the fusibility of the clay in degrees of temperature, and this temperature is measured by one or another form of pyrometer, whose principle depends on -the fusion of alloys or single metals; thermo-electricity; fusion of an artificial mixture; spectro photometry; expan- sion of gases or solids; etc. Many of these are only applicable at lower temperatures, others are largely influenced by the personal equation, and only two or three of the most important will therefore be mention- ed here. THE THERMO-ELECTRIC PYROMETER. Le Chatelier's Thermoelectric pyrometer depends on the measurement of a current generated by the heating of a thermo-pile. The latter consists of two wires, one of platium, the other an alloy, 90 per cent. platinum and 10 per cent of rhodium, twisted together at their free ends for a distance of about an inch, wlrle the next foot or two of their lenth is enclosed in a fire clay tube so that when the couple is inserted into the *Die Feuerfesten Thone, p. 71, 1876. § English and Mining Journal, March 10, 1894. 32 GENERAL DISCUSSION OF CLAYS. furance only the end which is held near the body whose temperature is to be measured, will receive the full force of the heat. The two wires connect with a galvanometer, the deflection of whose needle increases with the temperature at the point of the free end of the wire couple. As at present put on the market, the thermo-electric pyrometer, costs about $180 and this, together with the delicacy of tha galvanometer, has' tended to restrict its use. There is no reason however why one should not be made and put on the market for a much lower1 price. It is not necessary that the re- cording instrument should be in immediate vicinity of the kiln, but it may be kept in another room wliere it is safe from dust and' rough handling, and wires can extend from there to tie kiln. This pyrometer is con- sidered to be accurate to within 10 degrees Fihr. SEGER PYRAMIDS. These consists of different mixtures of kaolin and fluxes, which are compounded so that there shall be a constant difference between their fusing points. Segar's series were numbered from one to twenty, and the difference between any twoiconsecutive numbers is 36 degrees Fahr. A later series introduced by Cra- mer runs from .01 to .022 with a difference of 54 de- grees Fahr. between their fusing points, and in addition the higher numbers in the Segar series have been extended from number twenty up to number thirty-six. As these cones have been recently recalibrated, the fusing points of the various numbers together with their composition is given herewith.* * Taken from a recently issued circular of Thon Industrie Saboratorium in Berlin, where the cones are and were originally made. PHYSICAL PROPERTIES OF CLAYS. No. OF CONE. 0.5 022 0.5 Na3 O Pb O COMPOSITION. }i f 2 | 1 Si 03 B2 03 FUSION POINT CENT. 590 FUSION POINT FAHB. 1094 0.5 Na2 O ) r 2.2 Si Oa 021 0.5 Pb O } 0.1 A12 03 { 1 Bo 03 620 1148 0.5 Na2 O ) {2.4 Si 02 020 0.5 Pb O } 0.2 A12 03 1 P>2 03 650 1202 0.5 Na2 O ) f 2.6 Si 02 019 0.5 Pb O } 0.3 A12 03 1 1 Bo 03 680 1256 018 0.5 0.5 Na2 O Pb 0 } 0.4 Ala 03 {2.8 1 Si B2 02 03 710 1310 0.5 Na2 O ] {3 Si 02 017 0.5 Pb O } 0.5 A12 03 1 B2 03 740 1364 0.5 Na2 0 ) {3.1 Si 02 016 0.5 Pb O } 0.55 Al 2 03 1 B2 03 770 1418 0.5 Naa O ) {3.2 Si 02 015 0.5 Pb O } 0.6 AIa 03 1 B, 03 800 1472 014 0.5 0.5 Na2 O Pb O } 0.65 Al 2 03 f 3.3 { 1 Si B2 02 03 830 1526 0.5 Na2 0 ) {3.4 Si 02 013 0.5 Pb O } 0.7 A13 03 1 B2 03 860 1580 0.5 Na2 O "I ( 3.5 Si 02 012 0.5 Pb O } 0.75 Ala 03 B2 03 890 1634 0.5 Na2 0 ) {3.6 Si Oa Oil 0.5 Pb 0 } 0.8 Ala 03 1 B2 03 920 1680 0.3 K20 , 0.2 Fe2 03 {3.50 Si 02 010 I 950 1742 0.7 Ca O J 0.3 A12 03 0.50 B2 0, 09 0.3 0.7 K2 O Ca 0 } 0.2 Fe2 0.3 A12 03 0, r 3.55 J0.45 Si B2 0, 03 970 1778 34 GENERAL DISCUSSION OF CLAYS. No. OF CONE. 08 0.3 0.7 Ko O Ca O } 0.2 0.3 COMPOSITION. Fea O3 Ala O3 I 3.60 0.40 Si B2 Oo 03 FUSION POINT CENT. 990 FUSION POINT FAHR. 1814 07 0.3 0.7 Ko O Ca O } 0.2 0.3 Fe2 O3 A12 03 { 3.65 0.35 Si Bo 02 03 1010 1850 C6 0.3 0.7 K2 O Ca O } 0.2 0.3 Fe2 O3 A12 03 { 3.70 0.30 Si Bo 02 03 1030 1886- 05 0.3 0.7 K2 O Ca O j 0.2 0.3 Fe2 O3 Ala 03 { 3.75 O.25 Si B2 02 03 1050 1922 04 0.3 0.7 K2 O Ca O 1 0.2 0.3 Fe2 O3 AI8 O3 I 3.80 O.20 Si Bo 02 03 1070 1958 03 0.3 0.7 Ko O Ca O ! 0.2 0.3 Fe2 O3 A12 O3 ! 3.85 O.15 Si Bo 02 03 1090 1994 02 0.3 0.7 K2 O Ca O j 0.2 0.3 Fe2 O3 Ala 03 { 3.90 O.10 Si B, 02 03 1110 2030- 01 0.3 K2 O 1 r.7 Ca 0 j 0.2 0.3 Fe2 O3 Al- O3 ! 3.95 0.05 Si Bo 03 1130 2066 1 0.3 0.7 K2 0 Ca O ! 0.2 Fe2 03 r 0.3 Ala O3 \ 4 Si O2 1150 . 2102. 2 0.3 0.7 K2 0 Ca O ) 0.1 0.4 Fe2 O3 A1203 ! 4 Si 02 1170 2138 3 0.3 0.7 K2 O Ca O ! 0.05 Fe2 O3 ( 0.45 Ala O3 ( 4 Si 02 1190 2174 4 0.3 0.7 K2 O Ca O I 0.5 A12 O3 4 Si 02 1210 2210 0.5 A12 O3 0.3 K2 O ^ 0.7 Ca O J 0.3 K2 O ) I 0.6 A12 O 0.7 Ca O J 5 Si O2 6 Si O2 1230 1250 2246 2282 PHYSICAL PROPERTIES OF CLAYS. 35 No. OF FUSION FUSION CONE. COMPOSITION. POINT POINT CENT. FAHR. 0.3 K2 O 7 L 0.7 A12 03 7 Si 02 1270 2318 0.7 Ca O I 0.7 Al 0.3 K2 O3 1 I 0.8 AI2 O3 0.7 Ca O J 0.3 Ko O -I L 0.9 A12 O3 9 Si O2 1310 2390 0.7 Ca O J I 1.0 Al 0.3 K3 O ^ 11 0.7 Ca O J 0.3 K2 Oa 8 I 0.8 AI2 O3 8 Si O2 1290 2354 0.7 Ca O 0.3 K2 O 9 0.3 K2 O 10 }• 1.0 AIa O3 10 Si O2 1330 2426 0.7 Ca O 0.3 K3 O 1.2 A12 O3 12 Si O2 1350 2462 0.3 K2 O ^ 12 [ !••* AI2 03 14 Si 02 1370 2498 0.7 Ca O j 0.3 K2 O 1 13 - L6 Ala 03 16 Si .Oa 1390 2534 0.7 Ca O J 0.3 K2 O 14 J- 1.8 Ala 03 18 Si 02 1410 2570 0.7 Ca O 0.3 K2 O 15 )• 2-l Ala O3 21 Si Oo, 1430 2606 0.7 Ga O 0.3 K2 16 [• 2.4 A12 O3 24 Si O2 1450 2642 0.7 Ca 17 I 2.1 Ala 03 ° 1 r 2-- o J 0.3 Ko O \ [ 2.7 A12 O3 27 Si O2 1470 0.7 Ca O J L 3.1 AI2 03 0.3 K2 O } 0.7 Ca O J 2678 0.3 K2 O 18 [ 3.1 AI2 03 31 Si 02 1490 2714 0.7 Ca O 0.3 K2 O 19 [- 3.5 Ala 03 35 Si O2 1510 2750 0.3 K2 O ~\ 20 [• 3.9 A12 O3 39 Si O2 1530 27£6 0.7 Ca O J GENERAL DISCUSSION OF CLAYS. No OF FUSION FUSION CONE. COMPOSITION. POINT POINT CENT. FAHR. 0.3 K2 O ^ 21 L 4.4 A12 03 44 Si O2 . 1550 2822 0.7 Ca O 0.3 K2 O ^) 22 [• 4.9 Ala 03 49 Si O2 1570 2858 0.7 Ca O J 0.3 K2 O 23 [• 5.4 A12 O3 54 Si O2 1590 2894 0.7 Ca O 0.3 K2 O 24 \. 6.0 Ala 03 60 Si 02 1610 2930 0.7 Ca O I 6.6 AU 0.3 K2 O 25 I- 6.6 Ala O3 66 Si O2 1630 ' 2966 0.7 Ca O .3 K2 O 26 ]. 7.2 A12 O8 72 Si O2 1650 3002 .7 Ca O .3 K2 O 27 J. 20 A12 O3 200 Si O2 1670 3038 .7 Ca O 28 AI2 O3 10 Si O2 1690 3074 29 A12 O3 8 Si O2 1710 3110 30 Ala O3 6 Si O2 1730 3146 31 Ala O3 5 Si O2 1750 3182 32 A12 O3 4 Si O2 1770 3218 33 Ala O3 3 Si O2 1790 3254 34 A12 O3 2.5 Si O2 1810 3290 35 Ala O3 2 Si O2 1830 3326 36 Ala O3 2 Si O2 1850 3362 The theory of these pyramids is that the cone bends over as the temperature approaches its fusing point, and when this is reached, the tip touches the base. If the heat is raised too rapidly, those cones which con- tain much iron swell and blister and do not bend over, and the best results are obtained by the slow softening of the cone under a gradually rising temperature. For practical purposes these cones are considered sufficiently accurate. In actual use they are placed in the kiln at a point PHYSICAL PROPERTIES OF CLAYS. 37 where they can be watched through a peep-hole but at the same time will not receive the direct touch of the flame from the fuel. It is always well to put two or more cones in the kiln so that warning can be had not only of the approach of the desired temperature but also of the rapidity with which the temperature is rising. In order to determine the temperature of a kiln sev- eral cones of separated numbers are put in, as for ex. .07, 1, and 5. Suppose .07 and 1 are bent over in burn- ng but 5 is not affected, then the temperature of the kiln was between one and five; the next time 2, 3, and 4 are put in, and 2 and 3 may be fused but 4 remain unaffected, indicating that the temperature reached the fusing point of three. These pyramids have been much used by foregin manufacturers of clay products and are coming into use in the United States. Numbers .01 to 10 can be obtained for one cent each from Prof. E. Orton, Jr., Ohio State University, Columbus, Ohio. It is rather difficult to compare the thermo-electric pyrometer with Seger pyramids and say that either one or the other is better. The latter are well adapted to judge t'he completion of the burning. That is it may take the same amount of treat to burn a certain ware to the proper condition, as it does to bend over cone 5,so that when the latter goes over the burning is done. The cones do not however show whether the -temper- ature of the kiln is r'sing steadily or fast at one time and slow at another, or again whether or not it may have dropped temporarily. All of these last mentioned conditions are shown by the thermo-electric pyrometer, and a comparison of 38 GENERAL DISCUSSION OF CLAYS. conditions during burning, with the results obtained, may lead to a discovery of those conditions that will produce the best product. CHEMICAL EFFECTS OF HEATING. While the fusion of a clay may be looked upon in part as a chemical action, there are ot'her changes which take place in the clay before the temperature of fusion is reached. These changes are : The driving off of the chemically combined water. The burning of the organic matter. . The change of limonite to hematite by the loss of its combined water. The oxidization of pyrite to sulphate which by further heating loses its sulphur and is also converted into hematite. The driving off of carbonic acid from any carbonates of lime or magnesia which may be present. The general effect of these changes is first to make the clay more porous, but subsequently to increase its s'hrinkage, and in addition the color of the clay is changed. A chemical interaction between the components of the clay only begins with incipient fusion. SLAKING. Clays, when thrown into water, break up more or less completely, or in other words, they slake. The process is simply one of mechanical disintegration, which, however, has important practical bearings. Some 'homogeneous clays on being immersed split into a number of angular fragments, while others flake off into scaly particles, while still others crumble down to a powder. This slaking action proceeds slowly or PHYSICAL PROPERTIES OF CLAYS. 39 quickly depending on the toughness or density of the clay. Some clays slake completely in two or three minutes, while others may be little effected by an immersion in water of an hour or two. The practical importance of slaking i^ noticed first in the case of clays which have to be washed for mark- eting, for the quicker they fall apart when they are thrown into water, the more rapid and sometimes the more thoroughly will be the elimination of the impuri- ties. In the tempering the easy slaking of a clay is also of importance, permitting it to be more easily broken up and the more thoroughly mixed with water. ABSORPTION. This varies with the amount of organic matter, fer- ric hydrate, and the porosity of a clay, and increases with all three. As has already been stated the more water a clay absorbs the more it has to give off in dry- ing and the more difficult it is, especially in the case of fine grained clays, to avoid cracking. COLOR OF UNBURNED CLAYS. Ferric oxide and organic matter are the two great coloring agents of the raw clay. Organic matter gen- erally colors a clay gray, bluish gray, or black, while iron according to t'he condition of the oxide, or the presence of carbonate, may impart a red, yellow brown, or sometimes a gray color. For any given amount of organic matter or ferric oxide, the coloration will be much more intense the more sandy the clay. In general it may be said that, organic matter ex- 40 GENERAL DISCUSSION OF CLAYS. cepted, the purer clays are usually light colored, while the impure ones are yellow, red, or brown. Organic matter however, frequently masks the iron coloration, and makes it often difficult to determine the refractory nature of the material. Siome clays , which burn perfectly white may be colored black by organic matter as in the case of the sand clay from Pegram. Ferrous compounds not infrequently impart a gray or bluish tint to clay, and at times the lower part of a clay bed may be gray while the upper portion is yellow or red, due to the oxidation of the iron contained in it. THE MINERALOGY OF CLAYS. Most clays are so fine grained that it is impossible to determine the mineral constituents wHh the naked eye, and their recognition even microscopically, is sometimes a matter of diffculty. At the same time however, there are certain minerals, which are either present in all clays or are to be found in a great many of t'hem, and these will be mentioned in the order of their abundance. KAOLINITE. The mineral kaolinite is looked upon as the base of all clays, and while it is not wanting so far as we know in any of them, nevertheless, it is not as abundant as we have been apt to consider it, nor are the charact- eristic properties of clay wholly due to it. Kaolinite, whose formula is A1203, 2Si02, 2H20, or silica 46.3 per cent., alumina 39.8 per cent., water 13.9 per cent is e white scaly mineral crystallizing in the monoclinic system, the crystals presenting the form of small hexagonal plates. Its specific gravity is 2.2 MINERALOG Y OF CLA YS. 41 to 2.6 and its hardness is 2 to 2^. It is naturally white in color and plastic when wet but very slightly so. The microscope shows the kaolinite to be collect- ed in little bunches which can be broken apart by grinding and thereby increasing the plasticity.* Kaolinite is nearly infusible but a slight addition of fusible impurities lowers its refractoriness. A mass of kaolinite is called kaolin, and pure kaolin is practi- cally unknown. Many kaolins contain very minute scales of white mica, which under t'he microscope are hardly distin- guishable from kaolinite. It is not to be inferred that kaolinite always occurs in hexagonal plates, for in some clays scales of six sided outline are almost want- ing. QUARTZ. This mineral is present in sedimentary clays most- ly in the. form of rounded grains, and sometimes in crystals, while in residual clays the particles are most commonly angular. It is an extremely hard mineral, which will scratch glass and possesses a shell l^ke or conchoidal fracture, it is practically not attacked by the common acids, but is affected by alkaline solu- tions. This is one of the few mineral components of clay which, at times, occurs in grains of sufficient size to be recognized by the unaided eye. It may be color- less but the surface of the grain is not infrequently stained by a tlrn film of iron oxide. Feldspar might be mistaken for it, but the latter will not scratch glass. Flint or non-crystalline silica is sometimes present in clays. It usually has a muddy color and a con- choidal fracture. *G. H. Cook, Clays of New Jersey, Geological Survey, 1878. 42 GENERAL DISCUSSION OF CLAYS. Both quartz and flint are infusible at very high temperatures but the presence of other minerals may serve -to flux them. Quartz tends to diminish the shrinkage of the clay, and if wanting it has to be added during the process of manufacture. Its addi- tion also tends to decrease the plasticity. CALCITE. This mineral which is carbonate of lime, effervesces when moistened with muriatic acid, so that its pres- ence in clay may often be detected by the addition of this chemical. Calcite is a soft mineral and occurs in the clay, either in the form of little rhombohedral or powdery particles. Clays, which contain a large amount of it in finely divided condition, are said to be marly, and in some clay deposits certain layers may contain a larger percent- age of carbonate of lime than others. The carbonate of lime found in clays may be derived from particles of limestone ir the clay if it is a sedi- mentary one, or from the decomposition of lime-soda feldspar in the case of either sedimentary or residual deposits.. Percolating water may also introduce it into the clay. GYPSUM. Gypsum or the sulphate of lime is found in clay in the form of grains, needles, well developed crystals, or lamellar masses. It is so much softer than calcite that it can be scratched by the finger nail, often has a pearly lustre, is transparent, and does not effervesce when acid is poured on it. In hard burned brick gyp- sum simply acts as a flux, but in lightly burned ones MINERALOGY OF CLAYS. 43 it gives rise to soluble sulphates which cause efflores- cence. MICA. This mineral can be frequently detected by the nak- ed eye, owing to its high lustre, even when it is present in the form of very minute scales. It is seldom absent in clays and is usually found to an appreciable extent in even the best kaolins, for on account of its scaly nature and lightness, it remains suspended in water for a long while and is consequently very hard to re- move by washing; small amounts of white mica are rarely injurious. 'Mica is usually £ound in those clays which have been derived from the breaking down of igneous or meta- morphic rocks, such as granites, gneisses or schists, and two species are recognized in clay, i. e. biotite and muscovite. The former is a complex silicate of iron, magnesia, and alumina, and occurs as six sided plates or irregular scales usually of a dark color. As it easi- ly decomposes with the formation of iron oxide, it is not so apt to be found in clays as the muscovite, which is more resistant to weathering. The muscovite is sometimes called potash mica, although it also con- tains a small amount of iron and magnesia; it is of silvery white or light brown color. Mica decreases the plasticty of clay, and tends to make it flaky when wet, if in a finely divided condition. White mica tends to increase the refractoriness of a clay, and to exert very little fluxing action, even at moderately high temperatures. IRON OXIDE. This, next to quartz, is perhaps the commonest min- eral impurity of clay. It occurs as earthy grains, as 44 GENERAL DISCUSSION OF CLAYS. metallic scales or as a superficial coating on other mineral grains found in the clay. It dissolves quietly in muriatic acid. Iron may also occur in the clay as a constituent element of many silicates, and indeed the effect which it produces may be caused not so much by the actual amount of iron oxide which is present, but by the condition which H is in. Iron oxide is very apt to form concretions in the clay, and these concretions which generally have a shell-like structure, vary in diameter commonly from a fraction of an inch to several inches. Siderite, the carbonate of iron, which is also to be found in many clays, likewise forms concretions or opaque rounded masses, which effervesce on the .addition of warm muriatic acid. The exterior of these siderite concre- tions is not unfrequently altered to limonite, the brown or yellowish hydrated oxide of iron. Such con- cretions are hard and rock-like in their nature, and either have to be separated by screening the clay be- fore using, or crushed by passing the clay between rolls. PYRITE. This mineral is a compound of iron and sulphur, and the grains of it are easily recognized by their metallic lustre and their yellow color. It is a very common constituent of many fire clays, and occurs either in the form of small grains or concretionary masses of yellow crystals. Its briglit metallic surface will serve to distinguish H from limonite which has a dirty appearance. DOLOMITE. This is a double carbonate of lime and magnesia, and may occur in a clay in the same form as calcite, and the effect of it is practically the same. METHODS OF CLAY ANALYSES. 45 METHODS EMPLOYED IN MAKING CLAY ANALYSES.* The following brief statement of the methods em- ployed in making the analyses of clays for this report has been prepared by Dr. Charles Baskervilk, by whom the analyses were made : Moisture — Two grams are heated in a platinum crucible at 100° C. until they show a constant weight. The loss is reported as moisture. Loss on Ignition (combined water, and sometimes organic matter, etc.) — The crucible and clay are heated with a blast lamp until there is no further loss in weight. Alkalies — This same portion of clay, which has been used for determining moisture and loss, is treat- ed with concentrated sulphuric and hydrofluoric acids until it is completely decomposed. The acids are evaporated off by heating upon the sand-bath. The cooled crucible is washed out with boiling water to which several drops of hydrochloric acid have been added. The solution after being made up to about five hundred cubic centimetres is boiled, one-half gram ammonia oxalate added and made alkaline with ammonium hydroxide ; the boiling is continued until but a faint odor of ammonia remains. The precipitate is allowed to settle and is separated from the liquid by filtering and washed three (times with boiling water. The filtrate is evaporated to dryness and ignit- ed to drive off ammonia salts. The residue is treated with five cubic centimetres of boiling water, two or three cubic centimetres of saturated ammonium car- bonate solution are added and the whole is filtered *Reprinted from Bulletin No. 13, North Carolina Geological Survey, 1897. 46 GENERAL DISCUSSION OF CLAYS. into a weighed! crucible or dish. The precipitate is washed three or four times with boiling water and itihe filtrate evaporated to dryness. Five drops of sul- phuric acid are added to the residue, and then the cru- cible or dish is brought to a hot heat, cooled in a des- icator, and the alkalies are weighed as a sulphate. To separate the alkalies, the sulphates are dissolved in hot water, acidified with hydrochloric acid, suffi- cient platinum chloride added to convert both sodium and potassum salts into double chlorides; the liquid is evaporated to a syrup upon a water-bath, eight per cent, alchohol added, and filtered through a Gooch crucible or upon a tared filter paper. The precipitate is thoroughly washed with eighty per cent, alcohol, dried at 100° C. and weighed; the potassium oxide is calculated from the double chloride of potassium and platinum. When magnesium was present to as much as one- half of one per cent., the magnesium hydroxide was precipitated with barium hydroxide solution and the barium in turn removed by ammonium carbonate. When the amount of magnesium was less than the amount named, this portion of the ordinary process was not regarded as necessary. Silica — Two grams of clay are mixed with ten grams of sodium carbonate and one-half gram of pot- assium nitrate and brought to a calm fusion in a plati- num crucible over the blast lamp. The melt removed from the crucible is treated with an excess of hydro- chloric acid and evaporated in a casserole to dryness upon a water^bath, and heated in an air-bath at 110° C. until all the hydrochloric acid is driven off. Dilute hydrochloric acid is added to the casserole now, and t'he solution brought to boiling and rapidly filtered. METHODS OF CLAY ANALYSES. 47 The silica is washed thoroughly with boiling water and then ignited in a platinum crucible, weighed, and moistened with concentrated sulphuric acid. Hydro- flouoric acid is cautiously added until all the silica has disappeared. The solution is evaporated to dryness upon a sand-bath, ignited and weighed. The differ- ence in weight is silica. Iron Sesquioxide — The filtrate from the silica is divided into equal portions. To one portion in a reduc- ing flask is added metallic zinc and sulphuric acid. After reduction and filtration to free the liquid from undissolved zinc and carbon, the iron is determined by titration with a standard solution of potassium permanganate. Aluminium Oxide- -To the second portion, which must be brought to boiling, ammonium hydroxide is added in slight excess, the boiling continued from two to five minuts, the precipitate allowed to settle and then caught upon the filter, all of the chlorides being washed out with boiling water. T'he precipitate is ignited and weighted as a mixture of aluminium oxide and iron sesquioxide. The amount of iron sesquioxide already found is taken from this and the remainder reported as alumina. Calcium Oxide — The filtrate from the precipitate of iron and aluminium hydroxides is concentrated to about two hundred cubic centimetres, and the calcium precipitated in a "hot solution by adding one gram of ammonium oxalate. The precipitate is allowed to settle during twelve hours, filtered and washed with hot water, ignited and weighed as calcium oxide. When the calcium is present in notable amounts, the oxide is converted into the sulphate and weighed as such. Magnesium Oxide — The filtrate f^orn the calcium 48 GENERAL DISCUSSION OF CLAYS. oxalate precipitate is concentrated to about one hund- red cubic centimetres, cooled, and the magnesium pre- cipitated by means of hydrogen disodium phosphate in a strongly alkaline solution, made so by adding ten cubic centimetres of ammonium hydroxide (0.90 sp. gr.). The magnasium ammonium phosphate, after standing over nignt, is caught upon an ashless filter, washed with water containing at least five per cent, ammonium hydroxide, burned and weighed as mag- nesium pyrophosphate. The insoluble residue is determined by digesting two grams of clay with twenty cubic centiments of dilute sulphuric acid for six or eight hours on a sand- bath, the excess of acid being finally driven off. One cubic centimetre of concentrated hydrochloride acid is now added and boiling water. The insoluble por- tion is filtered off, and after being thoroughly washed with boiling water is digested in fifteen cubic centi- metres of boiling sodium hydroxide of ten per cent, strenth. Twenty-five cubic centimetres of hot water are added and the solution filtered through the same filter paper, the residue being washed five or six times with boiling water. The residue is now treated with hydrochloric acid in the same manner and washed up- on the filter paper, and free from hydrochlo^c acid, is burned and weighed as insoluble residue. A portion of this is treated as the original clay for silica, aluminium oxide and iron oxide. Another por- tion is used for the determination of the alkalies in the insoluble residue. Titanic Oxide — One-half gram of clay is fused with five grams potassium bi sulphate and one gram sodium fluoride in a spacious platinum crucible. The melt is dissolved in five per cent, sulphuric acid. Hydrogen dioxide is added to an aliquot part and the tint com- METHODS OF CLAY ANALYSES. 49 pared with that obtained from a standard of t'tanium sulphate. Sulphur (total present) — The sulphur is deter- mined b}^ fusing one-half gram of clay with a mixture of sodium carbonate, five parts, and potassium nit- rate, one part. The melt is brought into solution with hydrochloric acid. The silica is separated by evapora- tion, heating, resolution, and subsequent nitration. Hydrochloric acid is added to the filtrate to at least five per cent, and the sulphuric acid is precipitated by adding barium chloride in sufficient excess, all solu- tions being boiling hot. The barium sulphate is filt- ered off and washed with hot water, burned and weigh- ed as such. ferrous Oxide — is determined by fusing one-half gram of clay with five grams sodium carbonate, the clay being well covered with the carbonate, the top be- ing upon the crucible. The melt is dissolved in a mix- ture of dilute hydrochloric and sulphuric acids in an atmosphere of carbon dioxide. The ferrous iron is determined at once -by titration with a standard pot- assium permanganate solution. The rational analysis is made from the results ob- tained by the chemical analysis in the following way : The alumina found in the portion insoluble in sul- phuric acid and sodium hydroxide is multiplied by 3.51. This factor has been found to represent the average ratio between alumina and silica in orthoclase feldspar; therefore the product just obtained would represent the amount of silica that would be present in undecomposed feldspar. The sum of this silica with the alumina, ferric oxide and alkalies equals the "feldspathic detritus." The difference between silica as calculated for feldspar and the total silica in the insoluble portion represents the "quartz" or "free 50 GENERAL DISCUSSION OF CLAYS. sand." The difference between that portion of the sample insoluble in sulphuric acid and sodium hydroxide and the total represents the "clay sub- stance/' The method of analysis used to detrmine the mineralogical character of the clay is called the rational method, and when carried out in its simplest form, determines the amount of clay substance or kaolinite, quartz, and feldspar present 'n the clay. If carried out more completely, it enables us to calculate the amount of calcite or limestone (calcium carbon- ate)' iron oxide and even mica in the clay. THE RATIONAL ANALYSIS OF CLAY. The rational analysis of clay consists in resolving the clay into its mineralogical elements, thus giving a clue to its physical as well as its chemical properties. It is often utilized by manufacturers of porcelain and other high grades of ware as a guide in the compound- ing of their mixtures. The ordinary quantitative or ultimate analysis regards the clay as a mixture of oxide of the elements, although they may be present in entirely different combinations, such as silicates, carbonates, hydrates, sulphates, etc. This condition of combination is im- portant for it makes a difference in the behavior of the clay. Thus for instance, if silica is present in the form of quartz it will decrease the shrinkage and also increase the refractoriness up to a certain point, but if present as a component element of feldspar it serves as a flux and also increases the plasticity somewhat. It is not intended though that the rational analysis RATIONAL ANALYSIS OF CLAY. 51 shall fully supplant the ultimate one for eac'h serves its own purpose. The ultimate analysis may be used to supply in- formation on the following points. 1. The purity of the clay, by showing the propor- tions of silica, alumina, combined water and fluxing impurities. 2. Prom the ultimate analysis Ave can form a gen- eral idea regarding the refractoriness of the clay, for, other things being equal the greater the total sum of the fluxing impurities, the more fusible the clay. 3. T'he color to which the clay burns may also be judged approximately for the greater the amount of iron in the clay the deeper red will it burn, provided the iron oxide is evenly distributed, and there is not an excess of lime in the clay. If the proportion of iron to lime is as 1; 3, then a buff product results, provided the clay is only heated to incipient fusion or vitrification. The above conditions will be affected by a reducing atmosphere in burning or of sulphur in the fire gases. 4. Clays with a la'rge amount of combined water sometimes exhibit a tendency to crack in burning. This combined water would be shown in the ultimate analysis. 5. A large excess of silica would indicate a sandy clay. The connection between refractoriness and chemical composition may be illustrated by the following analvsis. 52 GENERAL DISCUSSION OF CLAYS. 2 3 Per cent. Per cent 69.50 54.90 13.00 18.03 6.40 6.03 .25 2.88. tr. 1.10 tr. 3.40 6.70 6.90 3.40 3.17 6.65 13.41 DEG. F. DEG. F. 2300 1900 The following analyses indicate this fact : l Per cent. Si02 47.20 A12O3 36.50 Fe2O3 2.56 CaO tr. MgO tr. Alkal'es H20 13.35 Moisture .50 Total fluxes 2.56 DEG. F. Viscosity or fusion point. Above 2700 1. Chalk Bluff, Marion Co., Ala., U. S. Geol. Surv. 18th Ann. Rep., Part V. (continued), p. 1128. 2. Fernbank, Lamar Co., Ala. Ibid. 3. Norborne, Mo. Mo. Geol. Surv., XI. Ann. Rep. This is practically the full extent to which the ulti- mate analysis can be used ; and t'here still remain to be explained a number of physical facts concerning any clay which happens to be under consideration. It frequently 'happens that two clays approach each other quite closely in their ultimate composition, and still exhibit an entirely different behavior when burn- ed. The explanation which most quickly suggests it- self is, that the elements present in the two clays are differently combined. Some method of resolving the clay into its mineral components, so as to indicate the condition in which the elements are present is there- fore practically needed. As kaolinite results from t'he decomposition of feld- spar, the kaolin is quite sure to contain some unde- composed feldspar, and also some quartz, and (in smaller amounts) mica, since the two latter minerals are common associates of the feldspar. If, now, we know the amount of feldspar, quartz and kaolinite or clay-substance in the kaolin, and the effect of these individual minerals, we can form a far RATIONAL ANALYSIS OF CLAY. 53 better opinion of the probable behavior of the clay in burning. When mica is present, it ^s dissolved out with the kaolinite and reckoned in as clay-substance, but it is rarely present in large amounts, and may perhaps alter the character of the clay-substance but little, for finely ground white mica possesses plasticity, and can be formed and dried without cracking. It is more re- fractory than feldspar, and holds its form up to 1400° C.* In the following table are given the ultimate and rational analyses of a number of kaolins, which show how a constancy of ultimate composition may be ac- companied by variations in the rational analysis: * G. Vogi, Chem. News, 1890, p. 315. 54 GENERAL DISCUSSION OF CLAYS. ! O OS CO • -^ * TH Tji l> 8 § Sow .§ o CD CO CO TH ' * i— • lO CO TH co OS Tfri ic «D O O TH O CD CO O CO 0 1O tance su rtz par S, «D a ^ ^ oc rS >• Q fl g "2 «8 .* fl 43 III III! •S £ •** r & * « >s * ;N CO ^ J2 fl *— •« fll 1411.111 RATIONAL ANALYSIS OF CLAY. 55 From this table a number of interesting conclusions may be drawn. Columns 1 and 2 represent two clays which agree very closely in their ultimate composi- tion ; but in the rational analysis there is a difference of 6 per cent, in the clay-substance, 12 per cent, in quartz, and nearly 19 per cent, in the feldspar. Nos. 3 and 5 and 10 and 12 also illustrate this point. In Nos. 6 and 7, one a German, and the other a North Carolina kaolin, the ultimate analyses are very closely alike, and the rational analyses also agree very well. This is frequently the case wrhen the clay-sub- stance is very high, between 96 and 100 per cent,, as in Nos. 9 and 11. A third case would be presented if the rational an- alyses agreed, but the ultimates did not. Such in- stances, however, seem to be much less common. The practical value of t'he rational analysis bears chiefly upon those branches of the clay-working in- dustry, such as manufacture of porcelain, white earth- enware, fire-brick and glasspots, which use materials with comparatively few fusible impurities ( iron, lime, magnesia). There is much concerning clays which sitll remains unexplained, but it seems probable that, other things being equal, two clays having the same rational com- position will behave alike. We can illustrate this point by the following tests made on wrashed kaolins from the vicinity of Senne- witz, near Halle, Germany. From the figures given below, it will be noticed that in the case of Nos. 1 and 2 there is a close agreement in the shrinkage, which amounted to about 10 per cent, whein the clay was heated up to the temperature of a hard-porceclain kiln. In Nos. 3 and 4 the shrinkage is very nearly the same, but greater than in Nos. 1 and 2, because the 56 GENERAL DISCUSSION OF CLAYS. rational composition has changed, there being a mark- ed increase in the amount of feldspar. If there hed been much difference in the size of the clay-particles of Nos, 3 and 4 or Nos. 1 and 2, the shrinkage in each case would probably have been dif- ferent. TABLE II. — Rational Analysis and Shrinkage of Clays. Shrinkage in Hard Porcelain Feldspar. Quartz. Clay-Substance. Fe2O3 Fire Per cent. Per cent. Per cent. Per cent. Per cent 1.59 33.86 64.55 0.75 10.20 1.21 38.39 65.40 0.73 10.10 8.64 31.69 59.68 0.30 12.90 8.25 35.15 56.60 0.30 12.00 The degree of fineness of the clay-particles, and per- haps their shape also, probably exert more influence on the shrinkage than has been imagined, but just how far this makes itself felt is still undetermined. As an illustration of the practical use of the rational analysis wre may take the following : Suppose that we are using for the manufacture of porcelain or fire-brick a kaolin which has 67.82 per cent, of clay-substance, 30.93 of quartz, and 1.25 of feldspar, and that to 100 parts of this is added 50 parts of feldspar. This would give us a mixture of 45.21 per cent, of clay substance, 20.62 of quartz, and 34.17 of feldspar. If now for the clay we had been using, we substitu- ted one with 66.33 per cent, of clay-substance, 15.61 of quartz, and 18.91 of feldspar, and made no other changes, the mixture would then contain 44.22 per cent, of clay-substance, 10.41 of quartz and 45.98 of feldspar. This last mixture shows such an increase in feldspar that it must give much greater shrinkage and fusibil- CLASSIFICATION OF CLAYS. 57 ity; but knowing the rational analysis of the new clay, it would be easy to add quartz or feldspar so as to bring the mixture back to its normal composition. The application of the method of rational analysis to impure clays is not quite as satisfactory, but at the same time not as necessary. In the treatment, the iron, if present as oxide, and lime or magnesia, if car- banotes, are dissolved out with the clay-substance. The silicate minerals are grouped with the feldspar, and the clay thus becomes divided into clay-substance (kaolinite, ferric oxide, lime and magnesia carbon- ates), feldspar or feldspathic detritus; and quartz. If the percentage of ferric oxide and carbonates is high, it is necessary to determine them separately in the ultimate analysis. In making a rational analysis, the clay is .'treated with strong sulphuric acid, which decomposes the kao- lin into sulphate of alumina and hydrous silica. The former is soluble in water, while the latter is removed with caustic soda, and we get an insoluble residue con- sisting of quartz and feldspar. In this residue the alumina is determined and the feldspar calculated. Another way of conducting the rational analysis, and one which is chiefly applicable when the clay con- tains other minerals besides the kaolin, quartz and feldspar, such as carbonate of lime, ferric oxide, or mica, consists in analysing the insoluble residue and calculating the mineral percentages from this. THE CLASSIFICATION OF CLAYS. As it is possible to find every gradation from the purest to the most impure clays any classification that is attempted, will necessarily be more or less unsatis- factory. It is of course possible primarily to make 58 GENERAL DISCUSSION OF CLAYS. two great divisons i. e. residual and sedimentary, and to these might perhaps be added a third class of clays, namely, those formed by chemical precipitation. Un- der each of the first two classes, it would be possible again to find every gradation from pure to impure. It is not possible to make any classification based upon the practical applications of the materials, for some clays are used for as many as four to five dif- ferent purposes, and it is probable that some classi- fication which simply recognizes four or five important groups is probably the most satisfactory and the least confusing. Hill makes the following divisions :* China clays. Plastic, ball, pottery clays. Brick clays. Refractory or fire clays. He furthermore makes another table based on the origin of the clay as found in the United States : I — WHITE BURNING CLAYS. 1. Rock or residual kaolin. 2. Indianite or Indiana kaolin. 3. Florida or sedimentary kaolins. 4. White burnine* plastic clays. II — COLOR BURNING CLAYS. Mixed clavs — 1. Brick clays, (Siliceous). 2. Marly clays, (Calcareous). 3. Pink clays, (Ferruginous). 2. Cement clayp, (Silico-calc^reous). 5. Alum clays. Altered clays (shale and slate). *U. S. Geol. Survey, Mineral Resources, 1893. MINING AND PREPARATION OF CLAYS. 59 A classification which has been made by Seger, the great German Ceramic Chemist, gives : 1. Yell o ir burning, containing lime and iron. 2. Red burning, non-aluminous, ferruginous clays, which are free from lime. 3. WJtitc ami i/ellow burning. These clays are low both in lime and iron. 4. White burning, low in iron and high in alumina, THE MIXING AND PREPARATION OF CLAYS. RPOSPECTING FOR CLAYS. Clay deposits are best seen in those regions where rivers and brooks have cut gullies and ravines, the clay showing on the sides of the cut. In such locations the thickness of the deposit and variation in its character vertically are well shown. Similar sections are to be loooked for along railroads. As the beds are apt to wash down it is necessary to clean the surface of the cut before taking any sample for tesiting, and even then great care must be observed to insure the sample being an average one. Apart from cuts the presence of clay can often be determined by the character of the vegetation, the na- ture of the soil, or upturned tree roots. The outcropping of clay in a ravine should not be depended on alone, but in addition borings should be made to determined the depth and extetnt of the de- posit, and persistance of the different layers if there is a variation in them. Shale often forms cliffs or steep slopes, at the base of which there may be a talus of partly weathered fragments and soft clav; in fact the outcrop of a shale deposit may be covered by the clay into which it has 60 GENERAL DISCUSSION OF CLAYS. slaked under the influence of weathering. In some localities this mellowed outcrop may be only a few feet thick, but in many it is of sufficient volume to sup- ply a small brick yard, without the necessity of at- tacking the fresh shale beneath. MINING OF CLAYS*- Clays, when soft and plastic, are mostly dug with pick and shovel, loaded on wheel-barrows, carts or cars and hauled to the works. If the deposit is broad and shallow the clay is usually dug at any convenient point; often any overlying sand or other useless ma- terial has been first removed and used for filling in or some other purpose. If the bank is located on the hillside, and has con- siderable/height, it is worked out in broad steps, the object of this being to prevent the bank from sliding in wet weather. When t'he bank is near the works, wrheel-barrows or carts can be used to haul the clay, but far distances, over 600 feet, it pays to lay tracks and use cars, haul- ed either by horse or steam power. Underground methods of mining are only used in case the amount of overlying material is very great. It is chiefly used for shale deposits. Steam shovels are employed for sandy clays or soft shales at some localities in the Uuited States, but most shales are mined by blasting, and the fragments thus ioosened are sent to the works. Where the clay is rough, and the face of the bank 12 or 15 feet high, a plan often followed is to under- mine it by picking at the base, and then inserting large wooden wedges at the top. This brings down *This does not include the mining of kaolin, which is treated separately. MINING AND PREPARATION OF CLAYS. 61 a large mass at once, the fall serving to break it up. While effective, this method is often attended with danger. MINING OF KAOLIN. Kaolin is usually sufficiently soft in nature to be mined by means of the pick and shovel. In some por- tions of the beds near Valley Head streaks of halloy- site are found in the clay, which are quite .hard, but they are of such a limited extent as not to cause much extra trouble. If the deposit is deep, narrow, or in- terbedded with other formations which are too thick to be removed by stripping, or if again the kaolin does not run regular in its composition, it is often advisable to follow the better portions of the bed, or the narrow vein if it is such, by means of shaft, levels, or slopes. These sometimes have to be timbered, at other times, as at Valley Head, they do not. In the case of deposits which are large and broad, it is most economical to operate them as quarry work- ings or open pits, digging out the material and loading it on the cars or wheel-barrows which convey it to the washing plant. If a pit is large and broad the sides, instead of being dug out vertically, should be left in benches to prevent the washing down of the bank. In North Carolina, where most of the kaolin depo- sits are vein formations whose depth is comparatively great as compared with their width, the method ad- opted is to sink a circular pit in the kaolin about 25 feet in diameter. As the pit proceeds in depth it is lined with crib work of wood, and this lining is ex- tended to the full depth of the pit, which varies from 50 to 100 or even 120 feet. When the bottom of the 62 GENERAL DISCUSSION OF CLAYS. kaolin has been reached the filling in of the pit is begun, the crib work removed from the bottom up- ward as the filling proceeds. If there is any overbur den this is used for filling in the pit, and as soon as pit is worked out a new one can be sunk in the same manner right next to it. In this way the whole vein is worked out, and if the deposit is large, several pits may be sunk at the same time to increase the output of the mine.* Hydraulic mining has been tried with some success in some very sandy loose-grained kaolins, but it would not work in any of the deposits in Alabama, which the writer has thus far examined. The method to state it briefly, consists in washing the clay down into the bottom of the pit whence it is sucked up by means of a pump and discharged into washing trough from the conveying pipe, it being sometimes necessary to have a scraper to stir or loosen up the clay in order to per- mit its being drawn up more easily. This is a cheap and rapid methed where it can be employed, but most kaolins are too dense and not sandy enough to allow of its being used. THE WASHING OF KAOLINS. As has already been stated, most kaolins have to be washed before shipment, and one of two methods may be employed, i. e. washing in tanks or troughing. With the first method or that of washing in tanks, the kaolin is thrown into large circular tubs filled with water, in which it is stirred up by means of revolving arms and the clay lumps thereby disintegrated. By this treatment the fine kaolinite particles as well as very fine grains of mica, feldspar, and quartz remain *H. BV°P, Clay Deposits and Clay Industry in North Carol'na Bulletfn No. 13, N. C. Geol. Surv., p. 54. MINING AND PREPARATION OF CLAYS. 63 suspended in the liquid while the coarser grains set- tle on the bottom of the tank. The water with the suspended clay is t'hen drawn off to the settling tanks. A modification of this consists in the use of a large cylinder closed at both ends and set in a horizontal position; through this cylinder passes an axis with iron arms, the revolution of the latter serving to break up the clay, which is discharged through a hopper at the top. A current of water passes through the cylinder and carries the fine clay particles with it while the coarse ones are left behind in the machine. The speed of the current has to be regulated by experiment, for if too much water is used coarse material will be washed out of the cylinder, and conversely, if the current is too slow t'he clay will not yield a sufficient percentage of washed product. One objection to this apparatus is that it 'has to be stopped from time to time to remove the coarse sand from the machine. The method most commonly used at the present day for washing kaolin, is by troughing and its gen- eral detail is as follows : As the kaolin comes from the mine it is generally discharged into a log washer, which consists of a semi- cylindrical trough in which there revolves a horizont- al axis, bearing short arms. The action of these arms breaks up the kaolin more or less thoroughly, depend- ing on its density, and facilitates the subsequent wash- ing. The stream of water directed into the log washer SAveeps the kaolin and most of the sand into t'he wash- ing trough, which is about 15 inches wide and 12 inches deep. It may be wider and deeper if the kaolin is very sandy; in fact it should be. The troughing is about 700 feet long, and to utilize the space thorough- ly, it is broken up into sections, 50 feet to each is a 64 GENERAL DISCUSSION OF CLAYS. good length, these being arranged paralleled, and connected at the ends, so that the water, with sus- pended clay, follows a zigzag course. This troughing has a slight pitch which is common- ly about one inch in twenty feet, but the amount, of pitch depends upon the kaolin, and whether the sand which it contains is fine or coarse. If the kaolin is very fine, and settles slowly, the pitch need not be so great and vice versa. A large quantity of very coarse sand in the kaolin is a nuisance as it clogs up the log washer, and upper end of the trough more quickly and causes so much more labor to keep them clean. As it is, considerable sand settles there, and, to keep the trough clear, sand wheels are used. These are wooden wheels bearing a number of iron scoops on their peri- phery, as the wheels revolve these scoops catch up a portion of the sand which has settled in the trough, and as each scoop reaches the upper limit of its turn on the wheel, it, by its inverted position, drops the sand outside of the trough. These sand wheels are an aid, but it is often necessary, in addition, to keep a man shoveling the sand from the trough. If the sand is finer it is not dropped so quickly, but is distributed more evenly along the trough, and does not clog it up so fast. The zigzag arrangement of the troughing has been objected to by some, as it produces irregularities in the current causing the sand to bank up in the corners at the bends, and also at certain points along the sides of the troughing.* The effect of this is to narrow the channel, and con- sequently to increase the velocity of the current, there- by causing the fine sand to be carried still further to- *E. Hotop, Thonindustrie Zeitung, 1893. MINING AND PREPARATION OF CLAYS. 65 ward the settling tank. This difficulty, which is not often a serious one, has been obviated either by hav- ing the troughing longer or by allowing the water and suspended clay, as they come from the log washer, to pass through a section of straight trough, and from this into another one, of the same depth but five or six times the width, and divided by several longitu- dinal partitions. The water and the clay then pass into a third section, twice as wide as the second, and divided by twice the number of longitudinal divisions. By this means the water moves only in a straight course, but as it is being continually spread out over a wider space it flows with an ever decreasing velocity. By the time the water has reached the end of the troughing, nearly all of the coarse grains have been dropped and the water is ready to be led into the set- tling vats, but as a further and necessary precaution it is discharged on to a screen of one hundred meshes to the linear inch, the object of this being to remove any coarse particles that might possibly remain, and also to eliminate sticks and other bits of floating dirt that are sure to find their way in. Two kinds of screens can be used, (1) stationary, and (2) revolving. The stationary screen is simply a frame with a cop ^ per cloth and set at a slight angle. The water and sus- pended kaolin fall on the screen, and pass through. A slight improvement is to 'have two or three screens which overlap each other so that whatever does not get through the first will fall on the second. If the vegetable matter and sticks are allowed to accumu- late, they stop up the screen, and prevent the kaolin from running through, consequently the stationary screens have to be closely watched-. The revolving screens are far better for they are 66 GENERAL DISCUSSION OF CLAYS. self cleaning. Such screens are barrel shaped, and the water, with the kaolin in suspension, is discharged into the interior and passes outward through the screen cloth. As the screen revolves, the dirt caught is car- ried upwards and finally drops; but instead of falling down upon the other side of the screen, it falls upon a board, which diverts it out upon the ground. The settling tanks, into which the kaolin and the water are discharged, may be and often are about eight feet wide by four feet deep, and fifty or more feet long. As soon as one is filled the water is diverted into another. The larger a tank, the longer will it take to fill it, and allow the kaolin to settle, and delays due to this cause them to be expensive, especially when the market takes the output of washed kaolin as soon as it is ready. Small tanks have the advantage of permitting the slip to dry more quickly, especially when the layer of clay is not very thick, and furthermore a small pit also takes less time to fill and empty, but one dis- advantage urged against a number of small tanks is that a thorougly average product is not obtained ow- ing to the thin layer of settlings and the small amount iii each. In addition to this a series of small tanks requires considerable room. The advantages claimed for large tanks are that the clay can be discharged into any one for a considrable period, and, if the clay deposit varies in character, the different grades get into one tank and a better average is thereby obtained. If the kaolin settles too slowly, alum is sometimes added to the water to hasten the deposition. When the kaolin is settled, most of the clear water is drawn off, and the cream like mass of kaolin and water in the MINING AND PREPARATION OF CLAYS. 67 bottom of the vat is drawn off by slip pumps and for- ced by these into the presses. , The presses consist simply of flat iron or wooden frames between which are flat canvas bags. These bags are connected by nipples with a supply tube from the slip pumps, and by means of the pressure from the pumps nearly all of the water is forced out of the kaolin and through the canvass. When all of the water possible, is squeezed out the press is opened and the sheets of semi-dry kaolin are taken out. It is then dried either on racks in the open air or in a heated room. As for every ton of crude kaolin usually only about two-fifths 01 one fourth of a ton of washed kaolin is obtained, it is desirable to have the washing plant at the mines, for it avoids the hauling of 60 to 70 per cent, of useless sand which has to be washed out before the kaolin can be used or even placed on the market. II. GEOLOGICAL RELATIONS OF THE CLAYS OF ALABAMA, BY EUGENE A. SMITH, PH. D. The basis of all clays is kaolinite, the hydrated silicate of alumina resulting from the chemical decom- position of alumina bearing minerals which occur as essential constituents of igneous rocks. In this de- composition, as Dr. Kies has shown, the soluble con- stituents are leached out while the kaolinite remains behind as an insoluble residuum, more or less mixed with the other nsoluble matters of the original minerals. In this form the clay might be called a chemical clay, since it is the direct result of a chemical decom- position, having undergone no further modification by being taken up, transported and redeposited. There is another form of residual clay which may be distinguished from the above, and that is the clay resulting from the decomposition of impure limesltone. Naturally this variety is usually less free from foreign matters than the otter. These residual clays taken up and redeposited by running waters are incorporated in the stratified de- posits of any later age. The clay deposits of the different geological form- nations of Alabama have each its well marked pecu- liarities, and the geological formations are clearly de- 70 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. fined, so (that an account of the geological relations of these clays becomes a guide at once to the several va- rieties, and to their geographical distribution. ARCHAEAN AND ALGONKIAN. These two formations include in Alabama all the crystalline rocks of both igneous and sedimentary origin. It is generally acknowledged that kaolinite, which is the basis of all clays, has its origin in the de- composition of the minerals composing the igneous rocks, the chief kaolinite producing mineral being feldspar. It is. therefore, in the area of our crystalline or metamorphic rocks that we are to look for the origi- nal deposits of kaolinite. More especially, it is the granites, the pegmatites or graphic granites, that occur the largest proportion of feldspar, and consequently yield the largest proportion of kaolinite, and of the granites, thepegmatites or graphic granites, occurring in veins which traverse .the other crystalline rock, are by far the most important in this respect. The clays occurring in this form have been spoken of by Dr. Hies as vein clays*, and they are, as a rule, very slightly plastic, for the reason that they have not been subjected to the comminuting processes neces- sary to develop the highest degree of plasticity. A belt of mica schists with frequent veins of peg- matite, extends from Cleburne county and adjacent parts of Randolph, through Clay and Coosa into Chilton county, and in numerous places, the decay of the granite veins has given rise to the formation of deposits >olf kaolinite,. The other two constituents of these granites, viz., quartz and mica, occur like the feldspars in large masses, and thus the places which produce mica in large sheets are at the same time the ARCHAEAN AND ALOONKIAN. 71 places where the kaolinite is to be found. Below, a certain depth from the surface the feldspar of these granitic veins hsrs escaped t'he action of the atmos- phere, and is in its original form, while nearer the surface it has generally been converted into kaolinite. It is evident that in all these primary or original de- posits the kaoliuites mixed with the other and less destructible constituents of ithe granite, viz., the quartz and the mica, and by consequence all the kaolinite from such original deposits must be washed to free it from these substances. When ifhe granite or granitic rock contains comparatively little of iron- bearing minerals the resulting kaolinite will be cor- respondingly free from iron stain and of pure white color, and thus suitable for the manufacture of the finer grades of stone wrare or china. All the important deposits of this kind are, at the present time, at a distance from any railroad, and none of them have been developed in a commercial way. We have at hand very few analyses and itests made of these kaolinites. A material of tlrs kind from near Louina in Randolph county was analyzed many years ago by Dr. Mallett for Prof. Tuomey, with t'he following result: Analysis of Kaolinite from Louina, Randolph Co. Silica 37.29 Alumina 31.92 Ferric Oxide trace Potash, Lime and Magnesia 0.72 Water 15.09 Undecomposed Mineral 14.28 Prof. Tuomey remarks upon the absence of iron in this kaolinite as most favorable to its use in making fine porcelain ware, and he predicts that when Ran- dolph county has communication by railroad with the 72 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. outside world, the occurrence of porcelain clay in the county will become a matter of economic importance. These pegmatite veins with their mica and kaoli- nite, are very numerous in the upper half of Kandolph county, and also in the adjacent parts of Cleburne and Clay, and test pits have been sunk in hundreds of places to show up both the kaolinite and the mica. Dr. Caldwell of the Elyton Land1 Company, 'had this kao- linite thoroughly tested both as to its suitability for. the manufacture of porcelain ware and as to its re- fractory character. The pottery ware made from it came in competition with the best pottery wares in America and took a prize ait the. Art Institute Fair in Philadelphia, in December, 1890. Brick made from it also was subjected to the 'highest temperature of the furance and was declared practically infusible. These deposits lie near Milnei, Pinetucky, Micaville, in Eandolph, and near Stone Hill, Mr. Jas. Denman's and other places in Cleburne. The same belt extends southwestward through Clay and Coosa into Chilton, and has been tested at various places along this line. In this region of the crystalline rocks, one may everywhere observe the gradual (transition from the solid rock through decayed schists into complete soil, which is generally a clayey loam, more or less stain- ed wih iron. A reddish clay is thus seen to be a part of the residual matters left by the general decay of ithe rocks of this section, but this clay is, as a rule, so much mixed with quartz, mica, fragments of un- decomposed rock, that it can serve very seldom for anything more than material for the manufacture of building brick. Residual clays of this character are of universal occurrence throughout (the region of our crystalline rocks. It is not difficult to understand how under certain CAMBRIAN AND SILURIAN FORMATIONS. 73 conditions, the finer portions of these residual clays may be taken in suspension in running waters and redeposited at greater or less distances from their place of origin in depressions, or along slopes. In this way are often formed secondary deposits of pretty fair plastic clays, sometimes mixed with sand in proportion to serve well as material for good build- ing brick. An illustration of this may be cited near Wedowee in Randolph county, and there are many instances where the residual clays of the country as well as these redeposited masses are utilized both for the manufacture of buildings brick of excellent quality, and for pottery purposes. CAMBRIAN AND SILURIAN FORMATIONS!. In these formations, the clay deposits are either the residual clays left from the decomposition gen- erally of the great limestone formations of the Cam- brian and Silurian, or concentrations of these resi- dual clays by redeposition in sink holes, ponds, and depressions; or the accumulation through sediment- ary action ,in the depressions of these later forma- tions, of (the chemical or vein clays of the Archaean. The two great limestones, above memtioned, are rarely pure but are mixed with chert or other form of siliceous matters, with iron, and with clay. Upon their decay under the action of the atmospheric agencies, these insoluble matters are left in the form generally of reddish loam or clay capped with cherty fragments, and impregnated1 with iron- Such residual clays are extensively used in all our valley regions for the manufacture of ordinary build- ing brick, for which they are very well adapted, the 74 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. brick being very durable, but not very sightly, since they are likely to be spotted where the clay contains more iron than the average. Occasionally, however, we find as result of subsequent rearrangement by leaching, concretionary adtion, or the like, these resi- dual matters differentiated from each other in a most remarkable way, so that beds of nearly pure white clay lie alongside of beds of brown iron ore, itsielf remarkably free from either clay or chert. The most notable of such instances is at Rock Run where the bed of white kaolin, analysis of which is given in the body of this report, No. A. S., forms one of the walls of a bank of limonite w'hich has for years furnished ore to the furance. In close juxtaposition to the ore and kaolin, here mentioned, is one of the beds of bauxite for which this region is well known. Kaolin beds of this residual nature are known in many other parts of the State, resting upon the Cambrian and Silurian limestones. Near Jacksonville, in Calhoun county, at Tampa in the same county, and in numer- ous other localities of similar nature, are limited beds of kaolin, none of which, however, have as yet been developed or worked. The following clays described below may be assign- ed to these formations; the china clays, No. 190, from near Gadsen and No. 205 from Kymulga; the fire clays, No. 191 from Peaceburg in Calhoun county and No. 127 from Oxanna in the same county; the stone- war^ clays. No. 204 from Blount county and No. 192 from near Rock Run. In most of 'the large limonite banks of the valley regions, these deposits of pure clay occur, usually known as clay horses, some of them are undoubtedly of sufficient extent to be of commercial value. Many CAMBRIAN AND SILURIAN FORMATIONS. 75 references to these may be found in the Report on the Valley Regions. While none of these clay deposits have as yet found a market, it may be well for the sake of completeness to give a few details concerning such as have been recorded. The references to t'he pages of the report on the Valley Regions, Part II, are also added. In connection with beds of limoni/te in S. 31, T. 24, R. 11 E., in Bibb county, mention is made of the fact that the ore lies imbedded in clay of red or yellowish red color, with streaks of a white clay (p. 495. ) In Talladega county, in the flatwoods, lying along (the line of the Columbus & Western Railroad, in the southeast corner of S. 2, T. 21, R. 3 E., a white plastic clay which is said to have been penetrated to a depth of 35 feet, is reported to have been struck in a well, (p. 606.) In the same county in S. 19, T. 19, R.5 E., in t'he Charlton limonite bank there is a large "horse" of white clay, extensive deposits of white clay are noticed in connection with other limonite banks in the immediate vicinity, (p. 616.) In Calhoun county, in T. 15, R. 8 E., and in Sec- tions 21 and 23, there are many diggings in beds of limonite, and in most of them are "horses" of white clay, (p. 702). Again in T. 14, R. 8 E., in the same county, near Tampa, on land belonging to A. H. Tullis, Section 6, in the red residual clays derived from the disintegration of the limestones of the county, along with barite and limonite in pockets, are found some deposits of kaolin of white color and considerable thickness, up to 10 feet. In Section 5 of same township and range, the kaolin is exposedd in a cut of the East and West Alabama Railroad where it is 10 feet thick, (p. 715.) 76 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. In Cherokee county, to ffche northward of the line of the Southern Railroad in Sections 1 and 2 of T. 12, R. 11, E., there are many banks of limonite which have been extensively worked, and in some of them beds or "horses" of white clay have beenx exposed. One of these in the Clay limonite bank, in Section 2, Ithe clay deposit is of great extent and several car loads have been taken from it and shipped to Chattanooga for manufacturing into fire brick. A similar white clay occurs in the Hickory Tree bank in Section 1, ( p. 759. ) The occurrence of the clay in the Dyke limonite bank, near Rock Run, is described on page 777. This is itihe kaolin whose analysis is given below under the number A. S. In the Washer bauxite band in S. 35, T. 12, R. 11 E., near Rock Run, and in the Warwhoop and other bauxite banks of the same vicinity, white clay and halloysite are of common occurrence. Some of these clays should be utilized. Some details concerning Ithem are to be found in the Valley Regions report, pages 780 to 789'. In the limonite banks to the eastward of Tecumseh furance in the same county, in T. 12, R. 12, E., clay "horses" are everywhere found separating the pock- ets of limonite, pages 792 and 793. Accumulations of good plastic clay, which have evidently been deposited in the depressions of the limestone or in ponds, are not uncommon in the area of the great limestone formations. One such near Oxford in Calhoun county, is utilized by the Dixie Tile and Pottery Company. Analysis and physical tests of this clay are given in the body of this r port. Of less purity on account of mixtures of sand, etc., similar deposits are numerous, and utilized in places, as, for example, the brick clay at DeArman- ville in the Choccolocco valley. SUBCARBONIFEROUS FORMATIONS. 77 SUB-CARBONIFEROUS FORMATION. In the Sub-carboniferous formation of Wills' Val- ley is found the best known deposit of pure white clay of this section. This clay occurs chiefly in the lower strata of the formation^ generally very close above the Devonian Black Shale. The deposits which have, up to the pre- sent time, been pretty well proven, are to be found in the upper or northeastern end of Wills' Valley, near the Georgia line, and on both sides of the valley. The most important of them, however, occur on the east- ern side of the valley. They have been described somewhat in detail by McCalley in Part II of his Val- ley Regions report, pages 175 to 182, from which the following details are compiled : The Red Mountain ridges, made up of the strata of the Clinton, Devonian (Black S'hale), and Sub- cajrboniferous formations, occur here as elsewhere in the State, on both sides of the valley. The ridge on the western side is, in general, lower and less con- tinuous than thalt on the eastern side. The clay occurs in the lower strata of t'he Sub-carboniferous, not far above the Black Shale, and it has been "pro- spected" and found to be present in the ridges on both sides of the valley for some ten or twelve miles from the State line southward. In the northwest corner of S. 3, T. 6, R. 9 E., on the west side of the valley, a test pit exposes the following section : Section on west side of Wills Valley, DeKalb Co. Chert ledge weathered into a sandy rock of yellow color 8 to 12 inches. Strata hidden by debris 2 to 3 feet. White clay, without grit, in places like halloysite 3 feet . Bluish colored clay 3 feet, Strata not exposed 25 to 30 feet. Devonian Black Shale.... 78 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. The white clay occurrs in many places in this vicinity, and is called chalk by the people. On the eastern side of the valley, the Red Mountain ridge, as stated above, is more prominent and con- tinuous than on the west. Near the State line, about Eureka station and thence southwestward for a couple of miles, the clays have been tested and in many places worked. They have a thickness aggre- gating about 40 feet, but are said to thicken up oc- casionally to 180 to 200 feet, of which as much as 60 feet is a fine white clay suitable for the manufactory of stone ware. Some of the clay is shipped from here to the potteries at Trenton N. J., and some of it goes to Chattanooga, Tenn. The Franklin (Ohio] Com- pany Mines are situated in t'he northern corner of S. 34, T. 4, K, 10 E. The clay is won by surface dig- gings, slopes, and tunnels, according to locality. The following section is obtained along the wagon road through the surface diggings and will give a fairly correct idea of the occurrence. Section at Franklin Company's Mines, DeKalb Co. Alternations of chert layers, 4 to 18 inches thick, with fine sharp siliceous powder of white and yellow color 12 feet. Chert of light yellow color, interlaminated with thin streaks of clay 12 feet. Clay, mostly of yellow color, but with seams of white clay . ...10 feet. Alternations of chert in layers of 2 to 8 inches thickness with clay seams 18 inches in thickness , 4 feet. Alternations of chert in layers 2 to 6 inches thick with white clay in irregular seams 6 to 12 inches thick 18 feet. Clay, very gritty, of white color and chalky appearance 10 feet. Clay and shale, the clay white and gritty, the shale green 10 feet. Devonian Black Sha.e In these mines in the upper twenty feet the clay is more siliceous than in the lower twenty fee/t. The siliceous clay is better suited for making fire brick, while the plastic clay is a potter's clay, command- ing a good price. The chert which is intersitratified SUBCARBONIFEROUS FORMATIONS. 79 with the clay is also of value in the manufacture of stoneware. In the N. E. J of the S. E. J of S. 4, T. 5, R. 10 E. are the Montague Clay Mines, worked by a tunnel on the southeastern side of the ridge. The clay is about thirty feet in thickness, some cf it having a brown cpl- oraltion, due to organic matter. It is quite uniform in composition for a distance for at least a mile in a northeast and southwest direction, is quite free from stains of iron but perhaps less plastic than the clay from some of the Other localities near by. Most of the clay here mined goes to Chattanooga for the man- ufacture of fire brick. Two analyses of the clay from these mines are given by Dr. Hies under the numbers 116 and 117* and they are classed by him as fire clays. Further southwest, along the ridge, we find other occurrences of the clay as in the S. W. * of t'he N. W. J of S. 12, T. 6, R. 9 E., where there is an old open- ing on a clay bed, which shows some four feet of clay. Still further south westward' in the N. W. J of the S. E. -J of S. 15, T. 6. R. 9 E., there are numerous sur- face diggings, and tunnels; in a clay bed thirty feet or more in thickness. Some of the clay of this deposit is of most beautiful quality, and especially well suited to the manufacture of the finest stone ware. A set of china ware, TOO pieces, made from this clay took a premium at the New Orleans Cotton Exposi- tion. In places the clay has streaks and stains, due to iron, and in other places it has a dark gray color, due to the presence of organic matter, which does not pre- vent its burning to a white color. Much of /the clay is adapted to the manufacture of fire brick as shown by the analyses of a sample collected by Dr. Ries, 80 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. number 119. Analysis, number 2 14, shows the quality of the purer and whiter variety. The clay deposits extend to within two or three feet of the Devonian Black Shale, thus fixing the occur- rence at the base of the Subcarboniferous formation. .Beds of potter's clay of this formation have also been noted at other localities, among them one in t'he railroad cut just north of Stevens' switch on the A. G. S. E. K., and another in Calhoun county in S. 19, T. 15, E. 6 E.* Hard white clay, like halloysite in appearance, has also been noticed at points in ithe Tennesseee valley, near Stevenson, and it is quite probable that search in that valley would be rewarded by the finding of deposits of the clay of commercial importance. COAL MEASUEES. In some parts of the coal fields, the under clays of the seams of coal have been utilized in the manufac- tory of pottery, as at Jugtown, near Sterritt, in St. Clair county ; r t For>t Payne and Eodentown, in De- Kalb; at Vance's Station, in Tuscaloosa county; at Summit, in Blount county, and at Arab, in Marshall county. In all these places the clay is manufactured into jugs, flower pots and similar articles, while at Fort Payne it is also used in the manufacture of fire brick. The shales of this formation are also utilized in some parts of the State, notably at Coaldale, where they are made into vitrified brick for paving purposes. At the Graves Coal Mine, near Birmingham, occur two bodies of shale, which have been analyzed and "Valley Regions, Part II., pages 441 and 741. CRETACEOUS FORMATION. 81 otherwise tested for this report, and. the results of these tests are to be found below, numbers 170 and 171. Dr. Ivies has tested also the Carboniferous shales from near Pearce's Mill, in Marion county, and finds them admirably suited for the manufacture of pressed brick and with a mixture of a more plastic clay suit- able for the manufacture of terra-cotta (No. 3.) Up to the present time none of the clays from the Coal Measures have been found suitable for use in the manufacture of high grades of fire brick, but this may be due to the circumstance that very few of these clays have beeen examined. Of shales suitable for making vitrified brick, there is the greatest abund- ance. CKETACEOUS FOEMATION. In many respects the most important formation of Alabama in respect of its clays, is the lowermost division of the Cretaceous, which we have called the Tuscaloosa. The strata composing this formation are prevalently yellowish and grayish sands, but subordinated to (these are pink and light purple sands, thinly laminated1, dark gray clays holding many well preserved leaf impressions, and great lenses of massive clays varying in quality from al- most pure white burning clays to dark purple and mottled clays high in iron. This formation occupies a belt of country extending from the northwestern corner of the State, around the edges of the Paleozoic formations to the Georgia state line at Columbus. Its greatest width is at the north-western boundary of the State, where it covers 82 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. an area in Alabama thirty or forty miles wide and about the same width in Mississippi. From here towards the southeast the breadth of the belt gradually diminishes, till at Wetumpka and thence eastward to the State line, it forms the surface along a belt of only a few miles width. To the eastward of the Alabama river, the propor- tion of clay to the rest of the strata is less than in the other direction, and at the same time the clays themselves are as a rule 'more sandy. But from the Alabama river northwestward, in the gullies, ravines, and railroad cuts, there are many exposures of these beds, exhibiting sections of clay beds from six to for- ty or fifty feet in thickness, and of varying degrees of purity. In a general way we may say that the purer clays, resmbling kaolin in composition, have as yet been found only in the northern part of this area in Fayette, Marion, Franklin and Colbert counties, and the adjoining parts of Mississippi. In my Coastal Plain Keport, published in 1894,* I have brought together many details concerning the Tuscaloosa formation in the counties of Lee, Rus- sell, Macon, Elmore, Autauga, Chilton, Perry, Bibb, Tuscaloosa, Pickens, Lamar, Fayette, Marion, Franklin and Colbert, and the reader is referred to that book for full discussion of the formation. In order, however, to present the clay occurrences as completely as possible I shall give extracts from the Coastal Plain Report in so far as they may be descriptive of the deposits of clay. To these extracts are added a number of details received from a report made by Dr. George Little, who in 1891, spent several months making for the Geological Survey ysome examinations of the clays *Pages 307-349, 531-2, 536, 541, 545, 549 554, 556, 559. CRETACEOUS FORMATION. 83 of ithis formation. Dr. Little brought together a large collection of the chief varieties of these clays and from these specimens, many of the analyses found in the report below have been made. Use is also made of manuscript notes of my own on examinations made since 1894 and of descriptions of clay occurrences in the report on the Valley Regions, Part I, by McCalley. Inasmuch as die remarks of Dr. Eugene W. Hil- gard on the clays of Mississipppi apply in general to the clays of this State which lie immediately ad- jacent to them on the east, a short extract from his Report on the Geology and Agriculture of Missis- sippi will not be out of place. These notes relate to the clays occurring in Townships 4, 5 and 6 in Tish- omingo county, Mississippi, and were published in Dr. Hilgard's Report on the Geology and Agriculture of Mississippi, 1860. "A large deposit of white clay of great purity, how- ever, occurs in Tishomingo c ounty, chiefly in the southern portion of the territory of the Carboni- ferous formation, following very nearly its western outline. It there forms a regular stratum of con- siderable extent, which .in onei locality at least, was found to be more than 30 feet in thickness. The bed attains its best development, so far as the quality of the material is concerned, in the northern portion of Township 5 and in Township 4, Range 11 east, where it is about 30 feet underground in the uplands, though at times appearing in limited outcrops on iihe banks of the streams. Northeastward and south- westward from the regions mentioned, the bed also occurs but changed in character, at least near the surface, to a white gritty hardpan, or clays of various colors and of much less purity. It forms the lowest 84 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. visible portion of the Orange Sand formation, and is almost invariably overlaid by strata of pebbles and pudding stone, which in their turn are sometimes overlaid by common orange-colored sand. The most southerly exposure of these beds, known to me, occurs on a small branch of McDouglas' Mill creek, in Sections 5, 4, and 9, Township 6, Range 10, east, near Mr. PannePs place. For more than a mile along this branch there are exposures in which about 20 feet of a whitish mass, varying from a fine •clayey sand to a white plastic clay, appears overlaid by thick beds (20 to 40 feet) of ferruginous pebble conglomerate ; the latter in its turn being overlaid by the common ferruginous sand and brown sandstone on the hilltops. Similar outcrops appear in the neighborhood of Mr. Aleck Peden's place on Sections 3 and 27 ^Township 5, Range 10 east, northeast, of PannePs Here also a white stratum of which only a few feet are exhibited is overlaid by pebble conglo- merate, and this by the common Orange Sand. The white mass varies from white plastic clay to fine grained aluminous sandstone; its upper layers are sometimes composed of a singular conglomerated mass, consisting of small, white quartz pebbles im- bedded *n pure white pipeclay. In both localities, copious springs of pure water are shed by the im- pervious clay strata. At Mr. Peden's, ithere is a fine bold chalybeate spring which seems, however, to derive its mineral ingredients (sulphates of iron and magnesia and common salt) from the adjacent Carboniferous strata rather than from those of the Orange Sand. In either of the localities mentioned, materials suited for fine pottery, or queenware, might be obtained. Thence northwest, the stratum is not often found CRETACEOUS FORMATION. 85 outcropping, but, as had been stated, 20 to 30 feet below the surface of the uplands; the country being but slightly undulating. At Dr. Clingscale's, Sec - tion 8, Township 5, Range 11. east, the clay stratum was struck at /the depth of about 30 feet beneath sand and pebbles; it was drug into, without being passed through, for nearly 30 feet more, no water being obtained from below, but dripping in above from the base of the pervious strata. The whiteness and plasticity of the material seems to increase with the depth. The portion of what was dug out of the well in question, had already been removed at the time of my visit, having been used for various economical purposes as, chalk, whitewash, and "Lily White". The specimens examined were, therefore, rather below the average quality, and on long exposure to the air, their surface shows some yellowish spots. I found nevertheless, that in baking at a high heat they yielded a biscuit of greater whiteness than their natural color when fresh; and that fine splinters, exposed for ten minu- tes to t'he highest heat of the mouth blowpipe, retain- ed their shape perfectly wrhile reduced to a semi-trans- parent frit. A quantitative analysis of the clay from Clingscale's well gave the following results: White Pipe Clay from Clingscales. Insoluble matter 90.877 J ime 0.140 Magnesia trace Peroxide of iron 0.126 Alumina 2 214 Water 6-930 99.864 This analysis (which was made solely for the pur- pose of ascertaining the ingredients foreign to the 86 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. clay proper) proves the singular fact that this clay, though occurring in a formation characterized by the large amount of iron it commonly bears, contains a remarkably small amount of that substance, which, together with minute porportions of lime and mag- nesia, explains its infusibility. The two most important practical purposes which the materials occurring in the deposits just describ- ed will serve, are the manufacture of fine queenware and that of fire proof brick. ( Not porcelain. Kaolin or porcelain earth contains, besides the white clay, a certain amount of undecomposed feldspar, which imparts to it its property of being semi-fused at the temperature of the porcelain kiln. The same prop- erty might be imparted to the white clay in ques- tion, by the artificial admixture of ground feldspar, but it could not thus compete with the naturel kao- lin of Alabama). As for the queenware, the plasticity of the mate- rial leaves nothing to be desired ; and since the amount of siliceous matter varies greatly in different lay- ers, there could be no difficulty about givng to the mass the precise degree of meagerness which may be found most advantageous, by mixing the several successive layers. The same may be said with reference to the manufacture of fire brick (to which these ma- terials are admirably adapted), which would proba- bly, at the present time, be the most feasible and most profitable manner in which the beds could be made available. The manufacture of fire brick differs from that of ordinary brick in this, that it requires more care, both in working the clay and in moulding the brick. Beyond their fireproof quality, it is demanded of fire brick that their shape be perfect, their mass uniform and without flaws in the interior; also that CRETACEOUS FORMATION. 87 they shall be liable to the least possible shrinkage in a high heat. The latter quality is imparted to them by a considerable mixture of either sand or ground fire brick to the fireproof clay, which itself ought to be thoroughly seasoned before, and then well worked up with such additions of the above materials as may be required. In judging of the amount of sand or ground brick to be added, it is to be observed, as a rule, to add as much as may be consistent with the proper firmness of the burnt brick and with conve- nient moulding. The latter process ought to be per- formed, as in the manufacture of pressed brick, when- ever a first-class article is aimed at, for it is only thus that external and internal flaws are entirely avoided. In some localities materials may be probably found which require no further admixture — the strongly sili- ceous varieties of t'he clay; but whenever sand or burnt clay is added to the mass, care should be had that it be free from iron, which would seriously im- pair the fireproof qualities of the clay. None but white sand should be used. For the rest, they may be burnt in kilns like common brick." RUSSELL AND MA CON COUNTIES. Within the limits of Girard and Phoenix Cit>, op- posite Columbus, and in the hills to the west of Gi- rard, are many exposures of the Tuscaloosa strata, aggregating some 200 feet in thickness. These are composed mainly of sands, but there are numerous beds of whitt,, gray and purple or mottled clays inter- stratified with the sands. The small stream which flows through Girard exposes a number of these clay beds, and others are to be seen in the hills to the west of the town. The materials for the manufacture of 88 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. drain pipe, vitrified brick, pressed brick etc., are here in abundance. These clays are to be seen at intervals along the road leading toward Montgomery, e. g., near Marvyn, Crawford and Society Hill, the prevailing variety be- ing the mottled red or purple clay. Northwest of So- ciety Hill these clays occur as far as FarrelFs Mill, in Macon county. Near Cowles' Station, at the ferry across the Talla- poosa river, purple clays, three feet in thickness, show in the river bank, and a short distance further down the river at the site of Old Fort Decatur, a fine sec- tion of the Tuscaloosia beds, including many beds of clay from one foot thickness and upwards is ex- posed.* ELMORE AND AUTAUGA COUNTIES. In the vicinity of Old Coosada town, along t!he banks of the river, about Kobinson Springs and Edge- wood, there are many occurrences of the clays of this formation, analyses of which have been made by Dr. Hies, and the results given below in the body of the re- port. About Edgewood there are several potteries and one ochre mine using the materials of the Tusca- loosa formation. McLean, Vaughn and Boggs have potteries here, and Pressley has one further west. At Chalk Bluff, near Edgewood, there is a very characteristic section exposed in an ancient bluff of the river, now at a distance of more than a mile from that stream. The section is as follows: "Coastal Plain Report, p. 554, 556. CRETACEOUS FORMATION. 89 Section at Chalk Bluff, Elmore County. 1. Layette red loam and pebbles 15 feet 2. Gray and yellow sandy clays, in distinct but irregular layers 6 " 3. White clay, 3 feet graduating downwards into yellow ochreous clay, 3 feet i " 4. Gray plastic clay blue when wet, and exceed- ingly tough and sticky ; full of vegetable remains, flattened and bituminized 10 " Two samples of this clay (Nos. 101 and 122) have been tested and analyzed by Dr. Kies (see below un- der the head of Pottery Clays and Brick Clays) , where a section of this bluff is given, differing slightly from the above. This is not bo be wondered at, since 'the stratification is very irregular, and no two sections, twenty feet apart, are idential. Along the line of the Mobile and Ohio Ky., in Auta- gua, and on most of the pubilc roads leading from Prattville north and northwest, there are exposures of Tuscaloosa strata, consisting of sands and clays, the former predominating. In the western or northwest- ern part of the county, near Vineton, many instruc- tive sections of the Tuscaloosa beds are to be seen. Some of these sections include beds of clay, which are of interest in our present work. Section, near Col. J. W. Lapsley's place, Vineton. 1. Stratified clays of white, pink, and purple colors, interlaminated with thin sheets of yellow sands : the lower part of this bed has a larger proportion of sand 10% feet 2. Gray laminated clay with partings of purple sands 5 " 3. Yellowish white laminated clays, with purple and other bright colors on the dividing planes, 5 feet showing, but the same beds appear to continue down the hill for at least ten feet further 15 " 90 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. ! Section No. 2, near the preceding. 1. Yellowish sands, beautifully cross-bedded.... 4 feet 2. White and pink clays, interbedded with yellow sands 10 " Section No. 3, same locality. 1. Purple clays interbedded with reddish sands.. 6 feet 2. Mottled (red and yellow) sandy clays, partly obscured by overl.ying pebbles and sands 12 " 3. Red sands with small lenticular bits of yellow clay 5 " 4. White and yellow laminated clays 6 to 8 " At the bridge over Mulberry, near Vineton, the fol- lowing strata are shown in the banks of the creek : Section on Mulberry Creek, near Vineton. 1. Mottled purple clays, similar to those at Steele's Bluff on Warrior River 5 feet 2. Yellow cross sandy beds 2 " 3. Mottled clays sandy below 5 " 4. Grayish white m caceous sands, with irregular patches of red and yellow colors ; to water's edge 4 " BIBB COUNTY. Prom Yineton up to Eandolph very little of the strata of the Tuscaloosa formation can be seen until within three miles of the latter place, where dark pur- plish gray clays are to be encountered. Between Ran- dolph and Centerville, along the public road, and at many points alon^ the railroad f^om Mapleville to Centerville, there are occurrences of the massive clays of this formation. These clays have given much trouble and caused much expense to the railroad, from the fact that when softened by the winter rains they squeeze out into the railroad cuts, filling them up and overflowing the track. Where the clays from the cuts are used to make embankments, they are equally troublesome, as they are continually giving way. We CRETACEOUS FORMATION. 91 have no accurate notes of the sections exposed, in the railroad cuts but the public road from Randolph to Centerville has been somewhat closely examined. At Soap Hill there is a typical section as follows : Soap Hill, 7 miles East of Centerville. 1. Purple and mottled clays at summit of hill ... 5 feet 2. Clayey sands in several ledges 10 " 3. Cross bedded yellowish and whitish sands, traversed at intervals by ledges of sandstone formed by the induration of the cross-bedded sands 30 4. Laminated gray clays with partings of sand. . 10 5. Alternations of laminated gray clays with cross-bedded sands in beds of 12 to 18 inches thickness 40 " 6. Yellowish cross-bedded sands with clay part- ings 20 " 7. Laminated gray sandy clays containing a few leaf impressions 10 " 8. Grayish white sands 8 " On the same road in the eastern part of the town of Centerville, on (the School House Hill, there may be seen some fifteen feet (thickness of purple andi yellow clays. The same beds show along the Selma road, south of Centerville, at many points. Sections are given in the Coastal Plain Report, pages 336 and 338. To the southAvest of Centerville also, in townships 21 and 22, ranges 7 and 8, many of (the ridges are composed of purple clays eight or ten feet in thickness, resting on four to six feet of gray clays.* On the road to Tuscaloosa the clays show about half way between Centerville and Scottsville. Along the line of the Alabama Great Southern Rail- road in this county, there are many exposures cf the Tuscaloosa clays, e .g. at Bibbville, where they have been utilized for many years in the manufacture of semi-refractory fire bricks for grates, etc. A great *Costal Plain Report, page 338. 92 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. deal of the material is shipped now to Bessemer, where it is worked up into fire brick. Further north, near Woodstock again are rather extensive diggings on t'he line of the Birmingham Mineral Railroad, from which the clay is shipped to Bessemer and used as above indicated. Dr. Ries has investigated the clays from both of these localities', and his results are given below in the body of the report, under No. 112 for the Bibbville's specimen, and No. Ill for that from Woodstock. He classes them with the fire clays. Another specimen from Woodsttiock, classed by Dr. Rle® as brick clay, has been tested, (No. 126, A. Stevens). TUSCALOOSA COUNTY. The utilization of t'he clays of this formation was begun in Tuscaloosa county by Daniel Cribbs in the year 1829. He was the pioneer, though it is said that W. D. Preston had a pottery in Autauga county in 1828. C. K. Oliver has had a pottery in this county since 1856. Peter Cribbs, in Lamar county, carried on the business for twenty-five years. He was the brother of Daniel, whose son, Harvey H. Cribbs, has for many years been more or less engaged in working the clays along Cribbs Creek, two miles south of Tus- caloosa, and1 later four miles east of town on the Ala- bama Great Southern Railroad. The Lloyd family have operated several potteries in Marion county, Al- abama, and Itawamba county, Mississippi, for many years. Fleming W. Cribbs, a son of Peter, has now a pottery at the nervv town of Sulligent,, on the K. C. M. & B. R. R,* Within the limits of the city of Tuscaloosa there *Notes of Dr. George Little. CRETACEOUS FORMATION. 93 are many exposures of the clays of this formation in were made. The best of the clay for these potteries was obtained from what is now Eeuben Powell's land, 2 miles west of the Military road in the northwesit quarter of the norhwest quarter of S. 28, T. 14, B. 16. The pits were dug 14 feet down to the clay, which was 3 feet thick. Mr. Powell has bored with an 8 inch augur near this place, and found clay 1^ feet from the surface, 5 feet thick, dark brown and very tough and plastic. Analysis of this1 clay is given by Dr. Ries, under No. 11 S. Lewis J. Jones, who now lives on the Powell place in the southwest quarter of south west quarter of Section 23, has bored a Avell in his yard of which the section is as follows : Section in Well, Lamar Co. Surface sands and loams 12 feet Clay 1 Ms feet Sand 9 feet Clay 2 feet White sand 24 feet Clay, penetrated to depth of 2 feet but so tough that the auger could not be raised, and the well was stopped. i Clay is also reported at Thomas' Mills, above Hun- neTs Bluff on Buttahatchie creek and on Wilson's creek near Friendship Church. WestAvard from the Military road, the clay (terri- tory continues to within 10 miles of Aberdeen, where level land and white sandy soil set in. Gattman is on the Mississippi State line, and just west of it across Buttahatchie is Greenwood Springs,4 miles from Quincy in Monroe county, Mississippi. 100 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. One and a half miles south of these Springs, there is a railroad cut 85 feet in depth, the largest cut on the road, (K. C. M. & B.) 110 miles from Birming- ham. In this cut we find the following section : Sections along K. C. M. & B. R. R., Lamar Co, Yellow loam 5 feet Yellow sand 15 feet Yellow sand with streaks of clay 5 feet Blue micaceous clay, sample No. 11, A 5 feet Half a mile further west another section : Yellow clay 5 feet Ferruginous sandstone, used for ballast 10 feet Yellow sand 20 feet Clay with sandy layers 8 feet Compact b'ue micaceous clay, sandy 12 feet At mile post 111, the section is : Red clay 10 feet Banded red and white r ay 10 feet Pore, sand 10 feet Half a mile west of the 111 mile post, the section is : Red loam of the Larayette formation > 5 feet Bright yellow sand 30 feet Clay 2 feet lAght yellow sandy clay 20 feet Red and white clay 5 feet Near the State line, on the Kansas City, Memphis and Birmingham Kailroad, 3 miles from Sulligent on the west side of Buttahatchie.a pottery has been oper- ated. At Sulligent, Fleming W. Cribbs has lately started a pottery. He is a son of Peter Cribbs and nephew of Daniel Cribbs. His clay bed is one-half mile east of Sulligent and is 4 feet thick, and white. He says that Irs father carried on the business from 1838 to 1853 when he died, and his widow continued the work to 1863, his account agreeing with that of the negro, Captain, nearly as to time of operation, CRETACEOUS FORMATION. 101 but placing it in entirely different decades. He has orders now for 5000 gallons (jugs) from Birmingham and Bessemer, at eight cents a gallon. He has two hogback kilns with a capacity of 800 jugs each. His clay is found in a washed out old road and is overlaid by 10 feet gravel. Rye has a pottery, 6 miles north of Millville, Detroit P. O. Davidson Brothers have one also in same neigh- borhood. Lloyd has one near the Mississippi line in Itawainba county. These compete with potteries at Holly Springs, Mississippi, and Pinson's 12 miles from Jackson Tenn., for the West Tenn. and Miss, trade. From State line at Gattman >to Glenn Allen, clays are very abundant and of fine quality all along the Kansas Citv Railroad, and this is destined to be an important center of trade in all kinds of clay manufacture. Beaver Creek flows nearly west, par- allel with the railroad. Beaverton is a station on Sec- tion 17, Township 13, Range 14 west. One mile west of William Brown's place, Section 10, and on Ed- mund Barnes', Section 16 and on Ira Sizemore's, Sec- tion IT, clay abounds. Brown has ten feet blue clay overlaid by 10 feet cross banded yellow sand. 5 miles east of Beaverton and 2 miles west of Guin, there is 10 feet white and yellow sand and underlaid by 3 inches of ferruginous conglomerate. FAYETTE COUNTY. Over the greater part of t'he area of Fayette county, the sitrata of the Coal Measures are covered, to a depth increasing as we go westward, by beds of the Tuscaloosa formation capped with the red loam and pebbles of the Lafayette. Among the strata of the Tuscaloosa there are many beds of clay of purple, gray and white colors. About the Court House, a bed 102 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. of white clay is reached at many points below a vary- ing thickness of overlying strata. Thus at Mr. Sam Appling's a bed of fine white clay, 6 feet in thickness, is cut in a well, and apparently the same bed is known ;to underly the region about: the depot. Mr. Appling's is in Section 24, Township 15, Range 13 west. Prom Dr. Little's notes, I am able to give a number of details of the occurrences of these clays. Seven miles from Fayette Court House, on the road to Mc- Collum's Bridge, is a bed of three feet thickness of very pure clay .hard and firm, which breaks up on ex- posure into nodules, and the same bed shows on an- other road to the west of this about one mile, south of Wallace's Mill on Gilpin's creek, on W. D. Bagwell's land. Dr. Ries' analysis of this clay is to be found in the report under number 67, S. On the road to Pikeville, seven miles from Fayette Court House, we have the following section : Section seven miles north of Court House, Fayette Co. Red loam of Lafayette 2 feet Gravel 10 feet Clay 3 feet Gravel 3 feet Between the depot and the Court House Dr. Little has observed three feet of good white plastic clay in a ravine on the roadside, and the same bed is exposed in the ravines at many points on the eastern edge of the old town. Five miles west of the Court House on the Vernon road, some tan-yard vats were dug years ago, three feet into a blue clay. About half a mile from t'he depot, Mr. Joe Lindsay reports fine white clay, twelve feeti below the surface, which, he says, was twenty feet thick. To the westward and southwestward of the town CRETACEOUS FORMATION. 103 along the line of the railroad, the clay shows in a cut one mile from 'the depot. On the Columbus road, four miles from Fayette, a six foot bed of clay is recorded, and five miles further west, at Hezekiah Wiggins' a bed of blue clay, four feet thick. Dr. Ries has tested and analyzed this clay under No. 32, S. Half a mile further west at Henry Wiggin's, there is a bored well, eighty feet deep, which, below the depth of fifteen feet, seems to be mostly in clay. One fourth of a mile beyond this, near Waldrop's, a bed of blue clay, 10 fet t'hick, shows at the bottom of a hill, and fifteen feet higher up another bed appears. Along the road to Tuscaloosa at seven miles from Fayette, and also a mile further on, clay, t'hree feet in thickness, is exposed. Again in section 13, township 17, range 12, about a quarter of a mile from Shirley's Mill, several beds of clay are shown along a hill side. One of (these beds, a brown clay, about three feet in thickness, is full of finely preserved leaf impressions, and below it a fine sandy clay of three feet thickness. This is near the 11 mile post from Fayette. Dr. Ries has analyzed two samples of the clay from this place under the numbers 68, S., and 110, and the reader is referred to these analyses and the remarks of Dr. Ries below. Two miles southwest of Shirley's Mill on Davis' Creek. J. W. Black reports four feet of blue clay in section 25, township 17, range 12 west. Near Doty's place, one mile east of Concord Church and about thirteen miles from Fayette, there is the following section exposed in a gully: Section near Doty's, Fayette Co. Red loam and sands of the Lafayette 4 feet Ferruginous sandstone crust 2 inches White clay (No. 7, Dr. Ries) 6 feet Yellow sand 5 feet Variegated clay (No. 71, Dr. Ries) 2 feet White sand 2 feet Mottled clay, red and white 3 feet 104 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. Dr. Kies' analyses of the two clays here exposed may be seen below under numbers TO and 71. MARION COUNTY. While the strata of the Coal Measures underlie the entire area of Marion county, yet these rocks do not form the surface over any great proportion of this area, since they are very generally hidden, except along the valleys of the streams, by overlying mea- sures of the Tuscaloosa and Lafayette formations. Among the strata of the Tuscaloosa, here as in Pay- ette, we find many fine beds of clay. Here again, Dr. Little has collected many details of the occurrence of these clays and what follows we take mainly from his notes, though use is1 made also of what has been pub- lished in my Coastal Plain Keport, pages 331, 332 and 333. In the lower part of the county along the line of the K. C. M. & B Railroad, clays are exposed in rail- road cuts all the way from Eldridge to Guin. From New River crossing near Texas P. O., on to Glen Allen, several beds of clay, of no great thickness, are to be seen. A mile east of Glen Allen, in what is known as Stewart's Cut, we have the following sec- tion: Stewart's Cut, one mile east of Glen Allen. Gray laminated clay with fine leaf impressions ... 25 feet Ferruginous sandstone crust of irregular thickness 1 foot Cross-bedded sands of yellow and pink colors 25 feet The uppermost of the beds, above named, contains many beautifully preserved leaf impressions which are very easily gotten out. The clay has been ex- amined by Dr. Ries under No. 18, S. At another cut, half a mile nearer Glen Allen, we CRETACEOUS FORMATION. 105 find twenty feet of white sand with two feet of white clay, and below this a blue plastic clay extending be- low the railroad track. This sand has been shipped to Memphis as mould- ing sand for the foundry. At Glen Allen, Dr. Little gives this section : Section at Glen Allen, Marion Co. Brown clay 12 feet Yellow sand 12 feet White pipe clay 2 feet Two miles east of Guin, on the same road, Dr. Little observes five feet of clay below a capping of red sand, and one mile west of Guin, (six miles from Beaver- ton ) he gives the following section : Section near Gwin, Marion Co. Cross-bedded yellow sands 10 feet Clay 4 feet Sand 3 feet Banded clay 3 feet Sand 3 feet On the South Fork of Buttahatchie in the vicinity of Pearce's Mill, there are several occurrences of clay and shale worth consideration. D~». Hies collected specimens from near the mill and gives his analyses of two samples under No. 1 and No. 2, both of which he classes as refractory or fire-clays. He also gives his tests of some shales of the Carboniferous forma- tion, which are well adapted to the manufacture of vitrified brick (No. 3). Another sample of hard and perfectly white clay was collected by Dr. Little from near t'he top of a hill one-fourth of a mile east of the mill. This Dr. Eies has analyzed under No. 36, S., and it is classed by him as a china clay. Dr. Little reports that, in pulverized condition, it is used as a face powder by the ladies in the vicinity. 106 GEOLOGICAL RELATIONS OF ALABAMA CLAYS. It is, however, in Townships 9 and 10 and Ranges 11, 12 and 13, that we find the most important de- posits of clay in this county. The typical locality of its occurrence is at Chalk Bluff, which gets its name from the white clay. Specimens collected by myself were analyzed by Dr. Win. B. Phillips and results published in the Coastal Plain report, page 346. Dr. Little's sample was collected on the land of J. J. Mit- chell, in northeast quarter of Section 8, Township 10, Range 13, from a bed five feet in thickness. The an- alysis of this is given below under No. 38, S., and on the same page Dr. Phillips' analysis is reprinted. This locality gives the name to the postoffice. In the same quarter section, Dr. Little has collected a sample from Briggs Frederick's land, and the analysis of this is given by Dr. Ries under No. 37, S. Another sample from the same locality from land of Mrs. Susan Nelson, has been examined by Dr. Ries (his number 85). The same clay is reported by Dr. Little as occurring southwest of Chalk Bluff at M. E. Gassett's, Section 13. Township 13, Range 10, as well as at a number of localities within a radius of five or six miles around Chalk Bluff. This clay is hard and white, approaching pure kaolin in composition. It is in a bed, five to seven feet in thickness, and needs only facilities for transportation to become one of 'the most valuable deposits in the State. Between Pikeville and Hamilton, clays are of fre- quent occurrence, one of these near the former place and some ten miles from Hamilton, collected by Dr. Little has been analyzed by Dr. Ries, (No. 65, S.) Westward from Hamilton to the Mississippi line and beyond, Dr. Little reports many occurrences of clay of various qualities. From the vicinity of Bexar, three samples of clay have been collected by CRETACEOUS FORMATION. 107 Dr. Little and analyzed by Dr. Ries, (numbers 12, 40 S. and 41 S.). The bed in this region is about four feet in thickness. Nos. 12 and 40 are from H. Palmer's and X<>. 41 from Bexar, a mile further west, near Pearce's Store and Mill. Near the State line on 8 -SV> Silica (total) 72.20 Alumina 17.42 Water and loss 7.40 Ferric oxide 2.40 Lime trace Magnesia trace Alkalies 56 Moisture.. .12 100.10 Free silica (sand) 52.31 Total fluxes 2.96 Specific gravity 2.28 This clay might work for an inferior grade of fire brick,. or also for pressed brick of a light color, or even for potter's clay. It resembles rather closely in composition a stoneware clay from Commerce, Scott Co., Missouri,* agreeing closely in every respect except the tensile strength. For sake of comparison the properties of the: Commerce clay are given herewith: Analysis of Clay, Commerce, Mo. Silica '71.78 Alumina 17.01 Water 8.13 Ferric oxide 2.01 Lime 34 Magnesia 43 Alkalies . .78 100.48 Total fluxes 3.56 Specified gravity 2.03 Incipient fusion 2000° F. Vitrificaton 2200° F. Viscosity 2400° F. Average tensile strength 225 Ibs. per sq. inch Maximum tensile strength 254 Ibs. per sq. inch *Mo. Geol. Survey, XI, 350. POTTERY OR STONEWARE CLAYS. 179 (No. 23 S.) STONEWARE CLAY. HEZEKIAH WIGGINS, FAYETTE CO. A light gray, hard, compact clay, of moderately silic- ious character and containing a few scattered mica scales. It slakes very slowly to tough scaly flakes. In order to make a workable pasie the clay requhed the addition of 34.3 per cent, of water. This paste was markedly plastic. Its shrinkage in drying was 14 per cent, and 8 per cent, in burning, giving a total shrink- age of 22 per cent. The tenacity of the air dried mass was on the agerage 232 Ibs. per square inch with a maximum of 300 Ibs. per square inch; which is exceeded by comparatively few clays. Incipient fusion occurs at 1900° F., vitrification at 2 100° F., and viscosity at 2300° F. The clay burns to a dense red body, but requires slow drying and heating to avoid cracking. The composition of this clay is as follows: Analysis of Stoneware Clay, H. Wiggins, Fayette Co. (No. 23 S.) I I Silica (total) 63.27 Alumina 19.68 Water 6.05 Ferric oxide 3.52 Lime 1.30 Magnesia tr. Alkalies 1.20 Moisture 3.75 88.77 i- r c silica (sand) 39.59 Total fluxes 6.02 Specific gravity 2.32 The clay agrees in composition in a general way with some of the stoneware clays of Missouri and Ohio, and its shrinkage and tensile strength are similiar to a ston 180 DETAILED REPORT ON ALABAMA CLAYS. ware clay from Harrisonville, Cass Co., Mo.,* but the lat- ter having nearly 3 per cent, more fluxes fuses at a lower temperature. (No. 65a. S.) POTTERY CLAY. TEN MILES SOUTHEAST OF HAMILTON, MARION CO. A moderately gritly, medium grained clay with a few mica scales, it required 28.9 per cent, of water to make a workable mass, which is rather lean. The air shrinkage of bricklets made from this was 6.5 per cent, with &n additional shrinkage of 5.5 per cent, in burning, making a total shrinkage 12 per cent. The average ten-ile strength of air dried briquettes was 58 Ibs. per sq. inch with a maximum of 6.5 Ibs. per square inch. Incipient fusion occurs at 1950° F., vitrification at 2150° F., and viscosity at 2350° F. It burns to a grayish buff color. The chemical composition is as follows: Analysis of Pottery Clay, 10 miles southeast of Hamilton, Marion Co. (No. 65af S. Silica (total). • ............................... 70 . 00 Alumina ................................... 21.31 Water ..................................... 6.35 Ferric oxide ................................ 2.88 Lime ....................................... 20 Magnesia ................................... tr. Alkalies .................................... tr. Moisture ................................... .50 i 101.24 Free silica ( sand) 45 80 Total fluxes 3.08 Specific gravity 2.10 *Mo. Ge-)l. Survey XI, p. 315. POTTERY OR STONEWARE CLAYS. 181 (No. 62 S.) POTTERY CLAY. THOMAS ROLLINS, FRANKLIN CO. A fine-grained tough clay, which slakts very slowly when thrown into water, but splits very easily along thin sandy layers which occur at intervals of about every half inch, a few mica scales are present, the addition of 20 per cent, of water gave a workable and quiet plastic paste. The shrinkage of bricklets made from this paste was 10 per cent, in drying, and 4 per cent, in burning, or a total of 1 4 per cent. The average tensile strength of air dried briquettes was 102 Ibs.per square inch, with a maximum of 127 Ibs. per square inch. Incipient fusion occurs at 1900° F., vitrification at 2100° F., and viscosity at 2300° F. The clay burns to a rtd- gray, but has to be heated very slowly, The composition of the clay is as follows: Analysis of Pottery Clay, Thomas Rollins, Franklin Co. (No. 62, S.) Total silica 67.50 Aumina ." 19.84 Water 6.15 Ferric oxide 6.15 Lime 12 Magnesia .10 Moisture . 1.50- Total 100.97 Free silica (sand) 43 46 Total fluxes 5.90 Specific gravity 2.36 (No. 55 S.) POTTERY CLAY (REFRACTORY.) J. W. WILLIAMS, PEGRAM, COLBERT CO. A white clay of fine grain, which slakes easily in water. The addition of 26 per cent, of water gave a lean 182 DETAILED REPORT ON ALABAMA CLAYS. workable mass which shrank 5 per cent, ia drying, and 10 per cent, in burning, giving a total shrinkage of 15 per cent. The average ttnsile strength of air dried briquettes per sq. inch is 30 Ibs , and the maximum ten- sile strength per sq. inch is 35 Ibs. Incipient fusion occurs at 2150 F., vitrificataon at 2300 F., and viscosity at 2500 F.; the clay burns to a dense yellowish white body. Following is the composition of the c'ay: Analysis of Pottery Clay J. W. Williams, Pegram, Colbert Co. (No. 55 8.) Total silica C6.45 Alumina 18.53 Ferric oxide 2.40 Water 8.68 Lime 1.50 Magnesia 1.25 Alkalies tr. Moisture.. .78 99.59 Free silica (sand) 44.22 Total fluxes 5.15 Clay base 49.44 Specific gravity 2.39 This clay could probably be purified by washing, it corresponds in general composition to a fire clay from Parker and RussePs Mine* near St. Louis Mo., but the latter on account of its greater coarseness, has a larger refractoriness. BRICK CLAYS. The term brick clays is a somewhat elastic one for it may include those used for the manufacture of common brick, front or pressed brick, and paving brick. As the requirements are somewhat different they can be men- tioned briefly and apart. Clays for common brick. For this purpose al-most any *Missouri Geol. Survey. Vol. XI, p. 570- BRICK OLA78. 183 clay suffices, in fact so little attention is applied to material used for this purpose, that the product is often soft and porous. Clays'for common brick should not* be excessively sandy, otherwise the brick will be weak and porous. They should possess sufficient plasticity to mould without cracking, but not be so plastic as to warp, due to excessive shrinkage. Most brick clays burn red. Fer- ruginous clays can be more safely burned to a hard pro- duct than clacareous ones, which burn buff or cream colored. The methods used for moulding common brick are the toft mud, by which the soft plastic mass is forced into the mould; and the stiff mud, in which the clay is forced from a die of rectangular cross section and then cut up into bricks. The latter method gives greater capacity, but the bricks unless thoroughly burned will not stand the weather as well. Very plastic clays and very lean ones are adapted to the stiff mud process, the former be- cause they are not tenacious enough, the latter because owing to their pastiness and the structure of the machine a laminated structure is developed in the brick. Brick clays should have a tensile strength not less than 50 Ibs. per square inch. They are not required to stand a high degree of heat, a few common brick kilns attain a temperature of over 1800 or 1900 degrees Fahr. The more rapidly the clay slakes the easier will it be to temper it. Clays for front or pressed brick. For this purpose a lighter grade of clay is required, and the material must not only burn to a hard body but also to a uniform color, for on the latter depends much of the beauty of the structure. In no branch of the clay working industry is the range of colors producible from natural clay mixtures more carefully considered than in the manufacture of pressed brick. ]84 DETAILED REPORT ON ALABAMA CLAYS. Many shades are obtained either by mixing two or more clays, or by adding artificial coloring agents to the raw materials. Clays for front brick should shrink evenly in burning, and not warp nor crack. Straightness of outline and evenness of size are essential to close fitting when set in the wall. Many front brick are moulded by the dry-press process, in which the clay is forced into the mould in the form of a dry powder. Such bricks have straight edges and smooth surfaces, but unless burned good and hard they chip easily. At many localities the clay is moulded in soft mud or stiff mud machines, and the brick, while still soft, re- pressed in a second machine whereby the surfaces are smoothed even and the edges straightened. These lat- ter brick do not tend to exhibit the same brittleness along the edges as the dry press brick are apt to. Front brick sell from $15.00 to $70.00 per 1000, de- pending on the color and shape. Clays for paving brick. The nature of these must be such that they can be burned to vitrification. To do this economically and on a large scale the points of vitrifica- tion and viscosity should be at least 125° F. apart and preferably 200° F. If they were not it would be impos- sible to bring a kiln full of bricks to vitrification without running them up to the temperature of viscosity. For this reason calcareous clays are not well adapted to pav- ing brick manufacture. Paving brick clays should possess moderate or good plasticity so that they can be moulded by the stiff mud process, and while it is desirable that the tensile strength should be 75 pounds or more, at the same time many good pavers are made from mixtures whose tensile strength is not over 50 pounds per square inch. Shales are used to a large extent for the manufacture BRICK OLA78. 185 of paving brick, partly because many of them contain about the right quantity and kind of fluxing impurities, and also because, owing to the fineness of grain, they vit- trify more evenly and thoroughly. Paving brick are at times made from fireclay, and the results obtained are excellent, but still shale is the favored mateiial. Except for comparing brick made from the same deposit, the color is absolutely no indication of the quality of a paving brick. The important properties which a paving brick should show are low absorption (under 2 per cent.) and resistance to abrasion. Crushing strength is of little importance provided it exceeds say 8,000 pounds per square inch. The brick clays described below come from several geological formations. The Graves' shales, Nos. 107 and 108 ; the Coaldale shale aud the Pearce Mill shale, No. 3, are Carboniferous shales. The Dixie clay and No. 128 and 129 of Mr. Stevens, are from the Poleozoic limestones, while the rest, No. 110 from Shirley's Mill, No. 122 from Chalk Bluff, Elmore Co.; No. 126 of Mr. Stevens, from Woodstock ; No. A, from Tusealoosa Co., are from the Tuscaloosa formation of the Sower Cretaceous. (Nos. 107 and 108.) BRICK-SHALES. W. H. GRAVES, BIRMINGHAM, JEFFERSON CO. Associated with the coal on the property of Mr. W. H. Graves are two beds of shale, viz: a yellow, sandy shale, and a gray one containing much less grit. Both of these were tested physically and the results of these tests are given below. The yellow shale contains a high per cent- 186 DETAILED REPORT ON ALABAMA CLAYS. age of ferric oxide and fuses very easily, while the gray shale contains several per cent, less, and is much better adapted to the manufacture of vitrified wares. The com- position and physical characters of the two are given side by side for the purposes of comparison. Light or gray shale, No. 108. Plasticity, quite good. The shale takes 25 per cent, of water to work it up. Air shrinkage 2 per cent. Shrinkage at 2000° F., 9 per cent. Brick good red color not, very porous. Shrinkage at 2200° F., 12 per cent. Brick reddish brown, and just about vitrified. Fusion a 2500° F. Tensile strength — average 105 pouuds, minimum 85 pounds per square inch. Dark or yellow shale, No. 107. Plasticity moderate; shale gritty, requires 20 per cent, of water to work it up. Air shrinkage 1 \ per cent. Shrinkage at 2000° F., 5 per cent. Brick good red color. Somewhat porous. Shrinkage at 2150° F., 6J per cent, Brick nearly dense, reddish towards brown. At 2250° F., nearly vitrified. Fusion at 2500° F. Tensile strength only 40 pounds to square inch. Analysis of shales, Birmingham, Jefferson Co. (No. Iffl and 108.) (108) (107) Silica 57.80 61.55 Alumina 25.00 20.25 Ferric oxide 4.00 7.23 Lime 2.10 tr. Magnesia 80 .988 Ignition 7.50 6.19 Alkalies 1.80 2.25 99.00 98.466 Total fluxes 8.70 8.45 Specific gravity . 2.12 2.23 BRICK CLA7S. 187 The gray sha^ bun s to a denser, harder body tl an the yellow, and does not blister as easily in burning ow- ing to its lower per centage of iron. PAVING BRICKS SHALE, COALDALE, ALA. A yellowish red, soft shale, with considerable grit. No mica or pyrite noticeable. Ground to 30 mesh and mixed with 22 per cent, of water it gave a lean paste, which shrunk 4 per cent, in drying and 5.5 per cent, in burning, giving a total shrink- age of 9.5 per cent. The tensile strength of the air dried briquettes was on the average of 25 pounds per square inch with a maxi- mum of 35 pounds. Incipient fusion occurs at 1900° F., vitrification at 2000° F., and viscosity at 2150° F. The shale burns to a red body and makes a good red brick. It is also used for paving brick. (No. 33.) RED SHALE, PEARCE'S MILLS, MARION co. There is an an extensive outcrop of partially weathered Carboniferous shale along the private road of Mr. Pearce just before reaching the millls. It is a red, rather fine grained material, and contains a small amount of mica. Its soft character renders the mining of it an easy matter. When ground the shale gives a moljrately plastic mass whose plasticity could no doubt be in reased by weathering. Forty per cent, of water were required to work it up, and the bricklets made from this material had an air shrinkage of 4 per cent. When burned to 2000° 188 DETAILED REPORT ON ALABAMA CLAYS. F., the to'al shrinkage w..s 8 per cent, and the color of the bricklet was a rich red. At 2100° F., the color of the bricklet was the same, and the -shrinkage was 9 per cent., incipient fusion having occurred at this point. Vitrification occurs at 2200° F., and the color is deep red, while viscosity took place at about 2300° F. In drying the clay showed little evidence of containing any appre- ciable quantity of soluble salts that would tend to form any efflorescence, nor did any show themselves afetr burning. The comparatively small shrinkage and the rich red color to which the clay burns would make it ad- mirably adapted to the manufacture of pressed brick, but unless it was mixed with a more plastic clay it would hardly work for the production of terra cotta. The semi-weathered character of the material would also facilitate the preparation of it. (No. A.) PAVING BRICK CLAY, TEN MILE CUT, TUSCALOOSA CO. .The sample of this clay was collected by the writer from what is known as the Ten Mile Cut on the M. & 0. R. R., west of Tuscaloosa. It is a somewhat gritty clay, which contains thin seams of sand. The general color of the clay is bluish-gray, but here and there it shows stains of limonite especially on the sandy fractures. Wh^n thrown into water it slakes and gives in working a some- \*hat gritty, but quite plastic mass, which requires 26.00 per cent, of water to work it up. The air shrinkage of the cky amounted to 8| per cent, while at 2200° F., it was only 10 per cent., and at 2300° F., 12 per cent., at which point incipient fusion occurred. BRICK CLAYS. 189 Vitrification took place at cone 27 in the Deville fur- nace and fusion above cone 30. The tensile strength of the air dried briquettes varied from 126 to 144 pounds per square inch with an average of 140 pounds. The clay burns to a buff color, and is to be classed as a refractory one although it is not highly so. Its location is excellent for cheap working, and easy shipment of the product, and while it has been put under the head of paving brick clays there is no reason why it should not find uses in other directions as well. The chemical composition of this clay is as follows : Analysis of Paving Brick Clay, Tuscaloosa Co. (No. A.) Silica 72.70 Alumina 19.61 Ferric oxide 934 Alkalies 80 Ignition 6.50 100.544 Total fluxes 1.734 PRESSED BRICK (LAY, DIXIE POTTERY CO., OXFORD, CALHOUN CO. This is the clay used by the Dixie Tile and Pottery Co. For the manufacturer of buff brick, the clay is quite plas- tic, and considering this fact it does not seem to require an extraordinary amount of water to work it up. The amount used being only 25.75 per cent. The average tensile strength is 130 pounds per square inch, with a maximum of 144 pounds. • In air drying the clay shrunk about 10 per cent ; at about 2200° F. incipient fusion be- gan, and up to this point the clay had burned a buff color but then began to burn to a grayish tint; vitrification took place at 2400°, and the total shrinkage to this point was 190 DETAILED REPORT ON ALABAMA CLAYS. 18 per cent. The clay fused or became viscous at 2600' F. The folio wiug is a composition of it : Analysis of Pressed Brick Clay, Oxford, Oalhoun Co. Silica 71.30 Alumina 17.16 Ferric oxide 1.94 Lime .60 Magnesia .43 Alkalies 95 Ignition 7.60 99.98 Total fluxes 3.92 This clay should make a good buff colored ware if burned at a comparatively low temperature, but if burned to vitrification the color would of course be much darker as indicated by the test, and owing to the high shrinkage in burning it would be necessary to conduct the latter slowly and with care to prevent cracking of the clay.* (No. 110.) PRESSED BRICK CLAY. SHIRLEY'S MILL, FAYETTE co. The clay from this locality is a very fine grained dense one, but at the same time breaks up very easily. It took 33 per cent, of water to work it up, and the air shrinkage of the bricklets was 6 per cent. Incipient fusion occurs at 2100° F. , Vitrification took place at 2200° F. and at this point, the bricklet showed a total shrinkage of 16 per cent., and a deep cream color. In the Deville furnace, at cone 27, the clay became viscous. *These bricks are well known in Alabama, and deserve to be even more generally usd than they are. E. A S. BRICK CLAYS. 191 While this clay is not to be looked upon as a refractory one, it would seem that owing to the beautiful color, to which it burns, it would be highly desirable for the manu- facture of pressed brick. The composition of the clay is : Analysis of Pressed Brick Clay, Shirley's Mill, Fayette Co. (No. 110.) Silica 71.32 Alumina 20.10 Ferric oxide 1.05 Lime tr. Magnesia 316 Alkalies tr. Ignition 7.505 100.291 Total fluxes 1.366 Specific gravity 1.90 (No. 1-22.) BRICK CLAY. CHALK BLUFF, ELMORE CO. The upper half of the clay bed at this locality is com- posed of a dark, dense, grayish brown clay which contains a large amount of organic matter, either in a finely divided condition or in the form of leaves. Although not sandy, at the same time it is rather lean when mixed up with water, and owing to the presence of so much organic ma- terial absorbed 40 per cent, of water when it was being worked up to a plastic mass. The air shrinkage was however only 6 per cent. At 1900° F. it had reached a total of 14 per cent., but the bricklet was still very ab- sorbent ; at 2100° F. incipient fusion had been reached and the total shrinkage was 18.7 j>er cent., while the color was brownish red ; and at about 2200° F. the total shrinkage was 20 per ceat. and the color brown, and this color had deepened considerably at 2250° F. with the ap- 192 DETAILED REPORT ON ALABAMA CLAYS. appearance of vitrification , while the maximum shrinkage amounted to 21 per cent. Viscosity was obtained in the Deville furnace at cone 27. This clay therefore thows an appreciable and safe dis- tance between vitrification and viscosity. The tensile strength is however low, averaging 75 pounds per square inch, with a maximum of 97 pounds per tquaie inch, and a minimum of 68 pounds. Specific gravity, 2.41. (No. 26 A. Stevens.) BRICK CLAY. WOOKSTOCK, BIBB CO. This is quite a plastic clay, which requires 29 per cent, of water to produce its maximum plasticity. The air shrinkage was 6 per cent., and the average tensile strength was 101 pounds per square inch, with the max - mum of 104 pounds. The fire test gave the following results : At 2250° F., the shrinkage 10 per cent, clay incipiently fused, color buff. At 2400° F., shrinkage 11 per cent., color a dark buff. At 2500° F., clay vitrified, color reddish. Viscosity occurs at cone 27 in the Deville furnace. The composition of the clay is : Analysis of BricTt Clay, Woodstock, J5i&6 Co. (No. 1£6 A. Steven*.) Silica 74.20 Alumina 17.25 Ferric oxide 1.22 Lime 30 Magnesia .40 Alkalies tr. Ignition 7.35 Total fluxes BRIOK CLAYS. 193 (No. 129, Stevens.) BRICK CLAY. BIRMINGHAM. This is a very dense hard clay, which required con- siderable grinding to break it up. The different lots were mixed up, and the one, A, being composed of two-fifths of the clay which was passed through 20 mesh sieve, and thee-fifths of particles greater than 20 mesh. The second lot, B, was made up entirely of that which had passed through the 20 mesh sieve. Both lots gave a rather lean mass, but A required 19 per cent, of water and B 16 per cent, to work up. The average tensile strength of A is 12 pounds, and that of B 35 pounds. The air shrinkage of both was 4 per cent. In burning to 2300° F. the shrinkage of A was 3 per cent, the color of the bricklet a full yellow, and the body very absorbent. At 2400° F. incipient fusion occurred in both cases, and the color of the bricklet was a brownish gray, and the total shrinkage 10 per cent. At 2500° F. the clay was vitrified, of a dull brownish gray color, and showed a very homogeneous fracture. Viscosity occurred at 2700° F. The chemical composition of the clay is : Analysis of Brick Clay, Birmingham. (No. J«9 Stevens.) Silica 67.30 Alumina 16.10 Ferric oxide 7.77 Lime tr. Magnesia tr. Alkalies tr. Ignition 9.25 Total fluxes ... 100.42 194 DETAILED REPORT ON ALABAMA CLAYS. (No.- 128, Stevens.) BRICK CLAY. ARGO, JEFFERSON CO. This was a very plastic smooth clay, which took 22.20 per cent, of water to work it up. The tensile strength varied from 120 to 136 pounds per square inch. The air shrinkage was 7£ j er cent. The behavior of the clay at other temperatures was as follows : At 2250° F. the shrinkage was 12 per cent., color yel- lowish gray. At 2300° F. the shrinkage and the color the same, but incipient fusion had begun. At 2500° F. the clay was vitrified, and the total shrink- age was 14 per cent. In the Deville furnace, at cone 27, the clay became thoroughly viscous. It could not therefore be called a very refractory clay, bat would work no doubt very well for pressed brick or for other purposes. The composition of the clay is as follows : Analysis of Brick Clay, Argo, Jefferson Go. (No. 128 Stevens.) Silica 72.87 Alumina 18.03 Ferric oxide 2.00 Lime .61 Magnesia 42 Alkalies .53 Ignition 6 62 Total fluxes MISCELLANEOUS -CLAYS. These are all derived from the Tuscaloosa formation of the lower Cretaceous. MISCELLANEOUS CLAYS. 195 (No. 67 S.) CLAY FROM W. D. BAGWELL'S, SEVEN MILES NORTH OF FAVETTE COURT HOUSE, FAYETTE CO. A gritty clay, that slakes slowly but completely to fine grains. The clay required 28 per cent, of water to make a washable mass, which was slightly plastic and gritty. This paste shrunk 6 per cent, in drying and 3 per cent, in burning, giving a total shrinkage of 9 per cent. The average tensile strength of the air dried briquettes was 45 pounds per square inch, with a maximum of 53 pounds. Incipient fusion occurred at 2100° F., vitrification at 2250° F., and viscosity at 2409° F. The clay burns to a deep buff color. Its composition is as follows : Analysis of Clay from W. D. Bagwell, Fayette Co. (No. 67. S.) Silica (total) 75,70 Alumina 14.36 Water 4.45 Ferric oxide 4.64 Lime tr. Magnesia tr. Moisture 1.24 100.39 Free silica (sand) 58.60 Total fluxes 4.64 Specific gravity 2.26 , (No. .40 S.) CLAY FROM H PALMER, BEXAR, MARION CO. A gritty, fine grained clay, containing scales of mica, which slakes easily and quickly to irregular grains. It required 26 per cent of water to make a workable 196 DETAILED REPORT ON ALABAMA CLAYS. paste, which to the feel was very slightly plastic and it tasted gritty. In shrinkage in drying was 6 per cent, and 3 per cent, in burning, making a total shrinkage of 9 per cent. Air dried briquettes of the mud had an average tensile strength of 66 pounds per square inch, and a maximum tensile strength of 68 pounds per square inch. Incipient fusion occurred at 2000° F.; vitrification at 2160° F. and viscosity at 2300° F.; at 2000° F. it burns to a buff, but on retrifying it becomes red in color. The composition of the clay is as follows : Analysis of Clay, H. Palmer, Bexar, Marion Co. (No. 40 S.) Silica (total) 71.33 Alumina Water Ferric oxide Lime Magnesia Moisture : 100.659 Free silica (sand) 46.45 Fluxes 859 Specific gravity 2.305 (No. 12.) CLAY FROM H. PALMER, BEXAR, MARION CO. A fine grained clay, with sandy laminae and mica scales between the layers. It slakes slowly to fine particles and grains of sand. The clay required the addition of 31 percent, of water and gave a moderately plastic mass, that shrank 5 per cent, in drying and 3 per 'cent, in burning, making a total shrinkage of 8 per cent. The briquettes made from this paste had, when air dried, an average tensile strength MISCELLANEOUS CLAYS. 197 of 85 pounds p.r square inch, with a maximum of 89 pounds per square inch. Incipient fusion occurs at 1950° F., complete vitrifica- tion at 2150° F., and viscosity at 2350° F. The clay burns to a yellowish red body. Its composition is as follows : Analysis of Clay, H. Palmer, Bexar, Marion Co. (No. 12) Total silica 09.93 Alumina 20.15 Water 5.90 Ferric oxide 1.38 Lime 42 Magnesia tr. Alkalies tr. Moisture 1.20 Total fluxes 1.80 Specific gravity 2.28 (No 41 S.) MOTTLED CLAY. BEXAR, MARION CO. A very open grained, sandy clay, with scattered scales of mica and occasional iron stains. It slakes very quickly to its component mineral grains. It required 39 per cent, of water to work it up. It is slightly plastic, and shrunk 6 per cent, in drying with an additional 11 per cent, in burning, making a total shrinkage of 17 per cent. Air dried briquettes of the mud had an average ten- sile strength of 15 Ibs. per square inch, and a maximum of 80 Ibs. per square inch. Incipient fusion occurs of 2000° F., vitrification at 2150° F., aud viscosity at 2300. The clay burns to a red, but not very smooth body. The clay analyzed as follows: 198 DETAILED REPORT ON ALABAMA CLAYS. Analysis of Mottled Clay, Bexar, Marion Co. (No. 41 S.) Silica (total) 72.40 Alumina 14.86 Water 5.05 Ferric oxide 7.64 Lime .20 Magnesia .40 Moisture .65 101.2o Free silica (sand) 55.20 Fluxes 8.24 Specific gravity 2.445 I (No. 18 S.) BLUE CLAY. THIRD CUT NEAR GLEN ALLEN, MARION CO. A very fine-grained soft clay with little grit, which slakes very readily on being thrown into water. It required 28 per cent, of water to make a workable mass which was slightly plastic. The shrinkage of this paste in drying was 8.3 per cent., and in burning 7 per cent., giving a total shrinkage of 15.3 per cent. The tensile strength of the air dried briquettes was 56 Ibs. per square inch on the average, with a maximum of 65 Ibs. per square inch. Incipient fusion occurs at 1950° F., vitrification at 2150° F., and viscosity at 2350° P. The clay burns to a light bluff. The composition on analysis was found to be as follows: Analysis of Blue Clay, R. R. Cut, near Glen Allen, Marion Co. (No. 18 S.) Silica (total) 68.10 Alumina 21.89 Water Ferric oxide Lime Magnesia .' Alkalies Moisture 99.230 Free silica (sand) 41.60 Total 4.19 Specific gravity 2.44 MISCELLANEOUS CLAYS. 199 The fineness of grain is probably accountable for the low tensile strength and comparatively low temperature of vitrification and fusion. As far as the composition is concerned it is not unlike some of the potters clays used it the United States, but its low tensile strength would probably act against its utility for this purpose, unless mixed with a more plastic clay. For building materials it would no doubt work all right. Being of fine uniform grain permits the production of a very smooth surface on the ware. (No. X. S.) CLAY FROM W. J. BECKWITH'S. • COLBERT CO. A moderately fine-grained, homogeneous, brittle, porous clay, with a semi-couchoidal fracture. In water it slakes slowly to particles mostly under one-sixteenth inch in size. When mixed with 28 per. cent, of water it gave a lean mass of somewhat gritty feel, which shrunk 5 per cent, in drying and 6 per cent, in burning, or a total shrink- age of 11 per cent. The clay had to be dried and burned slowly to prevent cracking. Air dried briquettes made of the mud had an average tensile strength of 22 Ibs. per square inch, and a maxi- mum strength of 38 Ibs. Incipient fusion occurs at 2050° F., vitrification at 2250° F., and viscosity at 2450° F. The clay burns to a deep buff body, and requires care- ful heating to avoid cracking. An analysis of the material gave the following results: 200 DETAILED REPORT ON ALABAMA CLAYS. Analysis of Clay, W. J. BecJewith, Colbert Co. (No. X S.) Silica (total) 58.20 Alumina 29.86 Water 9 12 Magnesia tr. Lime 20 Ferric oxide 2 22 Alkalies .....' tr! Moisture 1.18 100.78 Free silica 22.59 Total fluxes 2.44 Specific gravity 2.18 THE UTILIZATION OF CLAY FOR PORTLAND CEMENT. Aside from being used for the manufacture of clay pro- ducts, there remains the possibility of using some of the Alabama clays for the manufacture of Portland cement. The three essential elements of this material are lime, silica and alumina. The first of these is supplied by limestone, marl or chalk, while the other two are contain- ed in clay. In the manufacture of Portland cement the two mate- rials are ground and intimantely mixed after which they are burned to vitrification. During the burning certain compounds are formed, especially calcic aluminates and silicates, whose union with water and subesquent crystal- lization causes the cement to set. The mixture of clay and limestone is manipulated so that in the finished product, the per centage of lime shall be equal to 2.8 times the silica plus 1.1 times the alumina and to main- tain this constancy requires that the composition of the materials used must be constantly watched. While it is possible to get a proper cement mixture from materials showing an appreciable range in composi- tion, at the same time care must be exercised. Highly UTILIZATION OF CLAYS FOR PORTLAND CEMENT. 201 siliceous clays or limestones are undesirable, the materi- als used often contain ferric oxide, magnesia or alkalies. Their affect according to Shewberry is as follows: Ferric oxide combines with lime at a high heat and acts like alumina in promoting combinations of silica and lime. For practical purposes the presence of ferric oxide in a clay need not be considered in calculating the amount of lime required. Alkalies so far as indicated by the bebavior of soda, are of no value in promoting the combination of silica and lime, and probably play no part in the formation of cement. Magnesia though possessing marked hydraulic pro- perties when igniled alone, yields no hydraulic products when heated with clay, and probably plays no part in the formation of cement, and it is incapable of replacing lime in cement mixtures. The following analyses taken from the 1897 Mineral Industry will give an idea of the composition of clays used in portland cement, while following them are several Alabama occurence that could no doubt be used in ce- ment manufacture. 202 DETAILED REPORT ON ALABAMA OLAT8. 1 S2 iH O CO «D C-' Tt< OS t - «D CO IO *" j i 3SSS5S IS CO 00 GO K9 O O QO O Oi iH CO iH rH M • 1C Q CO : co 00 .os . O bo oo co oo . . . 0 O «*„ 6* (M C l> O IN 00 CD GO' 0 Bexar, Marion Co., clays near ,. 106, 107, 194, 196 Bibb County clays 75, 90, 150, 151, 191 Bibbsville, Bibb Co., clay at 91, 92, 133, 134, 150 Big Sandy Creek, Tuscaloosa Co., clay on^ 94, 95 Binding power of clays, see tensile strength Biolite in clays : 43 Birmingham clay 192 shales 184, 201 Bishop, quoted 31 Bitter taste of clays 21 Black, J W., Fayette Co., quoted 103 Black cores in bricks 15 Bleaching of clays 17 Blistering of clay ware 15 Blount County clays 74 igo Blue clay, Marion Co 197 Bluff and Brush creeks, Lauderdale Co., clay between Ill Bogg's pottery, Elmon Co 88 Bohemian kaolin, analysis of 54 Bone china of England 18 Borings, clay in 99? 103 Box spring, Tuscaloosa Co., clay of 93 203 CLAYS OF ALABAMA. Page. Brainard, A. R, quoted 123 Brick clays 72, 73, 76, 88, 92, 97, 181, 190, 191, 192, 193 '• loams 112 11 manufacture 90, 109, 150 " shales 184, 185 Bricks iu TJ. S. in 1897, valuation of 1 •' vitrified 80 Brown, Wm., Lamar Co., clay of 101 Brush and Bluff creeks, Lauderdale Co. , clay between Ill Buff ware v 18 Buhrstone flint clays 112, 158 Building brick clays 72 , 73 " " loam 112 Burned clays (grog) 27, 132 Burleson, Franklin Co., clays near 108 Calcareous clays 17, 183 Calcite 16, 42 Calcium oxide determination 47 Caldwell, Dr., quoted 72 Calhoun County clays 75, 80, 134, 135, 188 " " kaolin ; 74 Cambrian clays 73, 133 Carbonate of lime in clays 16, 17 Caraonate of iron in clays 44 Carboniferous plastic fire clays 131 Centerville, clays near 90, 91 Chalk 78, 85, 201 Chalk Bluff, Elmore County 88, 89, 162, 184, 190 " " Marion Co 6,25,26,52,106,117,127 Charleston limonite bank, "clay horse'' in 75 Chaney's pottery, Franklin Co 108 Chemical and physical properties of clays 114 Chemical clay 58, 69 " effects of heating clays 38 " properties of clays 9 Chemically combined water of clays 22,24 Cherokee County bauxites 142 " " clays 76, 118, 136, 161 Chert for glazing 79 Chilton County clays 72 '• " mica schists 70 China ware clays 79, 110, 115, 116, 118 " kaolinite 71 Choctaw County clays 26, 112, 131, 134, 158 Claiborne formation flint clays 112 Clarke County flint clays 112, 131, 158 Classification of clays 57 Clay 3 Clay, chemical , 58, 69 INDEX. 209 Page. Clay County clays 72 " " kaolinite veins 72 " •' micaschists 70 •' " mica veins 72 " " pegmatite veins 72 "Chay horses " 74, 76, 76, 108 Clay origin 3 Clay produced in U. S. in 1897, valuation of. 1 Clay properties .» 1, 3, 8, 114 Clay prospecting 59 Clay rocks (shales) 7 "Clay substance" 9, 50 Clays, classification of. 57 " composition of 9 " distribution of. 8 " mining of 59, 60 " miscellaneous 193 " preparation of. 59 " for headstones of graves 107 44 for Portland cement 201,202 " for vitrified bricks 10 " for whitewash 110 Clays from feldspar rocks 5 '• " gneisses 5,16 " " granites 5, 16 " " limestone 5,73 " " Paleozoic shales 6 Clays, geological structure and distribution of. 6 " in sink holes, ponds, etc 73 " in veins 70 Clays of Alabama, geological relations of. 69 " " Mississippi........... ". 83 " *' Red Mountain, Wills' Valley 77, 78, 78 Clays, residual 5, 6 " sedimentary 5, 7 Cleburne County kaolinite veins 72 " " mica veins 72 ii '* micaschists 70 •' " pegmatic veins 72 Clingscale's, Dr., Miss., clays 85, 112 Coaldale, Jefferson Co., paving and vitrified bricks 80, 185 4< " " shales 184 Coal Measures, clays from 80, 131 Coastal Plain Report, quoted 82, 88,91,94, 106 Cobalt in clays ..... 116 Colbert County clays 82, 109, 129, 157, 180, 198, 202 Color burning clays 58 Coloring of clays by iron \ 13 Color of clays '... 15, 39 Combined water... 28, 45 210 CLAYS OF ALABAMA. Page. Common brick clays 181 " " in the U. S in 1897, valuation of 1 Composition of clays, see analysis Concord Church, Fayette Co., clay near 103 Obnecuh County flint clays 12, 131, 158 Cones, -Seger and Cramer 32 CcassaOounty clays,., 72 '* ll mica schists 70 Coosada, Elmore Co., clays near. 88, 165 Coosi Valley Region, fire clay of. 133 Cook, quoted 25 Cottondale, Tnscaloosa Co., clays near 93, 94 Codes' Station, clays at 88 Cracking of clays 27, 132 Cramer pyramids (cones) 32 Crawford, Kussell Co., clays 88 Greta eous clays 6, 8, 81, 117, 131, 133, 160 Cribbs, Colored, Capt., quoted 98 Cribbs, Dan., pioneer in making Alabama clay ware 92 Cribbs' Fleming W. Lamar Co., clay 100 " " " " " pottery 92, 100 Cribbs , H. H., Tuscaloosa Co., clay 92, 93, 166, 202 " " " " " pottery 92,93 Cribbs, Peter, Lamar Co., potteries .,. 92, 98, 99 Cribbs' Place, Lamar Co., clay of. 172 Crystalline rocks in Alabama 70 Davenport, C. C., Cherokee County., clay from 161 Davidson Bros, pottery 101 Davidson's Store, clay at 107 DeArmanville, Calhoun Co., claysof. 76 Denman, Jas. Cleburne Co., clays of :.- 72 Dekalb County clays.... 77, 78, 79, 123, 123, 146, 148, 149 Detroit P. O., potteries near 101 Distribution of clays 6, 8 Dixie Tile and Pottery Co., Oxford, clay of 76, 184,188 Dolomite 44 Dolomite in clays : 16, 19, 44 Doty's, W., Fayette Co., clay 103, 174,175 Drainpipe clays ,.... 88 Drain tile in U. S. in 1897, valuation of. 1 Drying of washed kaolin ' 67 Dry process of moulding bricks 183 Dyke's bauxite bank, Cherokee Co., clays of. 136, 137, 138.139, 140, 141 Dykes limonite bank, Cherokee Co., clays of. 76, 118, 136, 137, 138, 139, 140, 141 Earthenware clay 122 Eastport, Colbert Co., fine silica white at :.... 112 Edgewood, Elmore Co., clays near 88, 163 " " " ochre near 164 Efflorescence on clay wares 17 Eldridge, clay near .....: :....... 104 Aftyr UNIVERSITY INDEX. 211 Page. Elgin property, Bibb Co., clays on 151 Elmore County clays 88, 162, 163, 165, 190 England bone china 18 English and Mining Journal, quoted 31 Epsom salts in clays -20 Eureka Clay Mines, Dekalb Co., 122 European clays, silicia in 20 Fat clays 23, 25, 133 Farrell's Mill, Macon Co , clays near 88 Fayette County clays 82, 96, 101, 102, 103, 174, 175, 176, 178, 189, 194 Fayette C. H., clays at and near 25,102,103 Feldspar 70 Feldspar clays 12 " in clays '.... 16, 18. 28 " " kaolin 116 Feldspar of granite veins 71 Feldspar veins, clays from 6 Feldspathic detritus '..' 49 Fernbank clays, Lamar Co........ 22, 25, 52, 98, 173 " pottery '' " '.". 98 Ferric salts in clays 14, 39 Ferrous oxide determination........... 49 " salts in clays 14, 40 Firebrick 86, 87, 94, 132, 133 " «• clays 78, 79. 80,86,91,117 " '* manufacture 92,109,150 Fire brick in U. S. in 1897, valuation of .. 1 Fire clays 92. 94, 97, 105, 110, 112, 130, 131, 132, 133 Fire shrinkage in clays 26, £7, 28 Flint 41, 42 Flint clays 3, 112 130, 131, 158 Florida clays 6 Flower vases, manufacture of... 93 Fluxes in clays 10 ,29 Foreign clays for Portland cement 201 Fort Payne, Dekalb Co., clays near 80, 149 Fort Decatur, clays at old 88 France, kaolin from , 54 Frankfort, Colbert Co., clays near 110 Franklin (Ohio) Company mines, Dekalb Co 78 Franklin County clays 82, 107, 180 Friedrick, Briggs, Marion Co., clays of. 106, 127 Free silica in clays 20 Friendship Church, Lamar Co., clays near — ' 99 Front brick clays 182 Fusibility in clays - 29, 31 Fusing point of Seger cones 33 Fusion of clays . 38 Gadsden, clay near 74, 117, 119 Galtman, Marion Co., clays near 101 212 CLAYS OF ALAP tMA. Page. Garnet in clays 1-t Gassett, M. E. Marion Co., clays of. 106- General discussion of clays 3 Geological relations of clays 69 Geological structure and distribution of clays .. 6 Geological Survey of U. S., quoted 58 Germany clays 54 u kaolin 55, 56 Gilley's branch, Franklin Co., clays of. 108 Girard, Russell Co., clays near 87, 88 Glazing clay 162 Glass-pot clay 97, 154 Glen Allen, Marion Co., clays near 101, 104, 105, 197 Granite veins in Alabama 70 " " ,claysfrom 6 Graphic granites (pegmatites) 70 Graves, W. H., Binningnam, shales of. 80,184 Green's, J. B., Lamar Co., clay 173 " " " " " pottery 98 Greenwood Spring, Miss., clays near 100 Griffin's, H. H., Dekalb Co., clay 123 Grog 27, 132, 133, 158 Guin, Marion Co., clay near 101, 104. 105 Gypsum 18, 42 in days 16, 18, 42 Halloysite 61 Hamilton, Marion Co., clays near 106, 179' Hickory tree limonite bank, Cherokee Co., clay in 76- Hilgard, Dr. Eugene W., quoted 83 Hopkins, T. 0., quoted 155 Hornblende in clays 14, 19 "Horses," clay 74, 75, 76 Hotop, E., quoted 64 Hughes, J. R., Gadsden, clay of 119 Hull's Station, Tuscaloosa Co., clay near 94, 133, 152 Hungarian porcelain, lime in Ifr Hydraulic mining of kaolin 62 Hygroscopic water (moisture} in clays 22 Igneous rocks in Alabama , 70 Impervious clays .... 30 Impurities in kaolin 9 Incipient fusion of clays 29* Insoluble alkaline compounds in clays 12 Insoluble residue determination in clays 48 Iron in clays 12, 13, 14, 43, 47, 51, 115, 116, 159 Iron in beds with cteys, purinioation of , 74 Jacksonville, Calhoun Co., kaolin from 74 Jefferson County clays 192, 193 • ' '•' shale for brick and cement manufacture 184, 186, 202; John's Mill, Tuscalooaa Co., clay at 9& INDE: ~ 213 Page. Jones, Lewis J., clay in well of. 99 Jugs, manufacture of 93 Jugtown, St Glair Co., pottery and clay at 83 Kaolin... ...3, 5, 9, 41, 55, 56, 82 86, 106, 115, 116 " drying 67 u impurities 9 Kaolinite 3, 4, 9, 10, 40, 69, 70, 71, 123 composition 4, 10 ** from granite viens 71 in clays 40 " orgin 3 veins 72 Kaolin mining 61 " presses 67 " residual beds 74 lt veins 7, 61 " washining v 62 Kilgore's Mill, Dr., Franklin Co., clay near 108 Kymulga, Talladega Co., clays near 74, 117, 121 Lafayette formation in Lamar Co 98 Lamar County clays 98, 172, 173, 202 Lapsley, Judge J. W., (Vineton), Autauga Co., clays near 80, 90 Landerdale County clays Ill Leaching of clays 74 Lean c'ay 23 25 LeChatelier's thermo-electric pyrometer 31 Lignite in clays 22 Lilly white, clay used for 85 Lime determination 47 Lime in clays 16, 29, 51 159, 160 * * carbonate iu clays 17 " silicate in clays , 17 Limes one 201 " , clays from 73, 75 Limonite banks with ''clay horses" 74, 75, 76 Limy clays 18 Lindsay, Joe., quoted 102 Little, Dr. G., quoted... 82, 83, 93, 96, 97, 98, 102, 104, 105, 106, 107, 108, 109, 111 Lloyd's potteries, Marion Co 92, 101, 107 Limonite 44 Loess clays, silica in 20 Loss in weight of clays after shrinkage has ceased 27 Louina, Randolph Co., kaolinlte 71 Macon County clays -. 87 Magnesia determination 46, 47 " in clays 19 Mallett, Dr. J. W., quoted 71 Manufacture of fire brick 92 Mapleville, Bibb Co., clays near 90 Marion Co. clays, 82, 104, 126, 127, 128, 155, 156, 179, 186, 194, 195, 196, 197, 202 214 CLAYS OF ALABAMA. Page. Marion County shale 186 Marl 16, 201 Marly clays 18, 42 Marvyn, Russell Co., clays near 88 McCalley, Henry., quoted : 77, 83111 McDougalas' Mill, Miss., clay near 84 McLean's, Elmore Co., clays and pottery 88, 163, 165 Metamorphic rocks 70 Metamorphism . 7 Method of clay analyses 45 Mica 43,70 " in clays 12, 14, 25, 29, 43, 53 " schists v. 70 " veins 72 Micaville, Randolph Co., clays near 72 Milldale, potteries near 101 Millportclay 98 Milner, Randolph Co., clays near 72 Mine, ochre, Elmore Co : : 88 Mineral Industry, quoted 201 Mineralogy of clays 40 Mineral Paint and Tripoli Co., Florence 112 Mines, clay 78, 79, 116, 146 Mining of clays 59, 60 " kaolin 61 Miscellaneous clays 193 Mississippi clays 83 Mitchell's, J. J., Marion Co., clay 106, 126 Missouri clays 20, 52, 131, 155, 168 44 flint clays, silica in 20 " Geological Survey, quoted .....1, 155, 168, 175, 177, 179, 181 Moisture determination 45 Moisture in clays 22, 45 Molding bricks, processes of 182 Molding sand, Marion Co 105 Monroe County clays 131, 158 Montague Clay Mines,, DeKalb Co 79, 133, 146 Mottled clay, Bexar, Marion Co 196 Muscavite in clays 43 Natural glaze clay 162 Nelson's, Mrs. Susan, Marion Co., clay 106, 127 New Jersey clays 20, 78, 131 Nichol's, A. W., clay 98 Non-volatile and non-fluxing constitutuents of clays 10 North Carolina clays 20 " " Geological Survey, quoted 45.62 " " kaolin 54 " " " mining 61 Ochre (red chalk) 108, 164 '• mine, Elmore Co 188- INDEX 215 Pa«e. Odor of clays '. 11 Ohio clays 168 Ohio Geological Survey, quoted 168, 171 Oliver, C. K., Tuscaloosa Co., pottery of. 92 Orange Sand formation 84 Organic matter determination 45 »' " in clays 14, 22, 28, 39, 40 Origin of clay 3 Ornamintal bricks in U. S. in 1897, valuation of. 1 Oxanna, Calhoun Co., clays ! 74, 133, 135 Oxford, Calhoun Co., clays, 76, 188 Paint clay, Landerdale Co 112 Paleozoic clays 6, 160 Palmer's, H., Marion Co., clays 107, 194, 195 Pannel's place, Miss., clay on 84 Paving brick clays.... 137, 183 '« " shales 185 Peaceburg, Calhoun Co., clay from 74, 133 134 Pearce's Mill, Marion Co., clays 105, 107, 128, 133, 134, 155, 156 Pearce's Mills, Marion Co., shale •...81, 105, 117, 184, 186, 201 Peden, Aleck, Miss., clay 01 84 Pegmatites (graphic granites) 70, 72 Pegram, Colbert Co., c'ays near 40, 109. 110, 117, 129, 134, 157, 180 Pennsylvania glass pot clay 155 Phillips, W. B., quote.} 106, 127, 167 Phoenix City, Russell Co., clay near , — 87 Pholerite , 4 Physicial properties of clays 24, 114 Pickel, Dr., quoted Ill Pickens County clays 97, 170, 171 Pikeville, Marion Co., clays near 106 Pinetucky, Randolph Co., clays 72 Pipeclays 85, 88 Pipe, sewer, in U. S. in 1897, valuation of 1 Plastic clays 73, 76, 130, 131, 138 Plastic ball clay s of F:orida 6 Plasticity 4 Plasticity in clays 23, 24, 25 •' kaolin 116 Plistocene clays 112 Pond clay 73 Porcelain clays ^ 11, 71, 72, 86 116 117 Porce! ai n earth •••••• 86 Porcelain ware from Alabama 72 Potash determination 46 " in clays 11 Portland cement, clays for 199, 201 " , materials for 199, 201, 202 Potteries 80, 88, 92, 93, 98, 99, 100, 101, 107, 108 ^16 CLAYS OF ALABAMA. Page- Pottery clay... .73, 78 80, 93, 97, 129, 129, 159, 163, 165, 166, 169, 172, 174, 175, 176 179, 180 Pottery ware in U. S. in 1897, valuation of 1 Pottery ware from Alabama 72 Post Tertiary loams for building bricks 112 Powell's, Reuben, clay 99 Porosity of clay '. '. 39 Prattville clays 25, 28, 201 Preparation of clays 59 Pressed brick, clays for ? 88, 177, 182 188, 189 Pressed brick, shale for 187 Pressed bricks 86 " " in U. S. in 1897, valuation of 1 Presses for washed kaolin 67 Pressley's pottery, Elmore Co 88 Preston's, W. D., pottery, Autauga Co 92 Properties of clays 1, 3, 8, 114 Prospecting for clays 59 Purification of clays in limonite banks 74 Pyramids, Cramer and Se^er 32 Pyrite 44 Pyritein clays " 14, 44 Pyrometer, thermo-electric 37 Pyrometers • 31 Pyrometer, Seger 32 Pyroxene in clays 19 Quartz 41 Quartz as a grog 132 Quartz determination 49 Quartz in clays 18, 21, 28, 41, 42 Quartz in kaolin 116 Queen ware clay 86 Radiolarian clay 158 Railroad cuts, clays sliding in 90, 94, 96 Randolph, Bibb Co., clays near 90, 91 Randolph County clays 72, 73 " . " kaolinite 71, 72 " " mica veins 72 " ." micaschists ' 70 " " pegmatite veins :... 72 Rational analyses 56, 57 " <• of clays 50, 54, 147, 149 150, 152, 154 "