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Jan 1, 1948

By W. H. Schacht

IN THE Lake Superior District, the air indoors must be heated continuously during eight months of the year and occasionally during the remaining months. Incident with mining in this district, therefore, there is need for heating many of the buildings connected with these operations. In addition to the mine buildings, that is, shops, engine, houses, offices, change houses, etc., such public buildings as schools, library, and theater, when close to the mines, are often supplied from the mine heating mains. At the Copper Range Company's mines, Champion, Trimountain and Baltic, the heating surface thus supplied from the mine mains is over 50,000 sq. ft. (4645 sq. m.) which requires a steam consumption, at times, of 18,000 lb. (8165 kg.) per hour, or the equivalent of a rate of over 50 tons of coal per day (were live steam used). This figure is based on a consumption of 1/3 lb. per square foot of heating surface during the coldest weather, and provided the system is not wasting steam by blowing it to the atmosphere or into the return line on account of leaky traps, which so often is the case. Under the latter conditions, steam consumptions of three to four times the above rate are not uncommon. This shows that the cost of heating is of enough importance to be given serious consideration, especially at this time of rising prices of fuel. The power and heating value of exhaust steam are appreciated by most engineers, and its application for such purposes is general. At our stamp mills, the exhaust from the stamps is used to operate low-pressure turbines, thus reducing the former water rate per horsepower developed by more than 50 per cent.

Jan 8, 1920

Jan 1, 1888

By H. J. Denning, M. W. Brabbins, A. K. Isaac

The quality of a coalface floor is the essential element that enables powered supports to generate their designed loads in control of coalface strata. The paper introduces a technique for the appraisal of coalface foundation stability. A criterion of support efficiency, viz., the support pressure increase/strata convergence, is included in case study data obtained from investigations in the South Wales Coalfield, U.K.

Jan 1, 1984

By Gifford Pinchot

The proposition that forest reserves are, from the mining point of view, not only desirable but necessary, is not one which would have received enthusiastic support in. the West a year ago. It is, nevertheless, easily susceptible of proof. A short and simple statement of the facts has seldom failed to carry conviction as to the wisdom of the forest-reservation policy. Hostility to mining interests was never contemplated by the men to whom the forest reserves are chiefly due, and it is most unfortunate that the opposite belief should have obtained wide

Jan 1, 1899

By R. H. Pemberton

The principle of airborne electromagnetic prospecting is well-known. The basic geophysical texts in most cases discuss the main elements involved in electromagnetic prospecting. However, there is certainly little information available to the public concerning the present types of airborne electromagnetic systems being flown today by both contracting companies and some of the mining companies which have their own instruments. This is unfortunate since it is difficult for those people not conducting such operations to understand thoroughly the large variation in the electromagnetic instruments available.

Jan 1, 1961

By H. W. Graham

THE young metallurgist of today who thinks casually of the technical literature of the steel industry might conclude that little has been published concerning the Bessemer process. This conclusion is true as relating to the last decade or two, but there is a fairly voluminous Bessemer literature in the period of 1860 to 1910, Since that time, however, an entirely new level of metal-lurgical knowledge of steelmaking has been reached; and the present paper is simply an effort to look broadly from this new level and to bring the recorded history of the process up to date, It is an effort to appraise the acid Bessemer method of steelmaking in the light of today's technical knowledge thereof. In this paper matters of history will be dealt with only insofar as they contribute to an understanding of today's situation. Attention will be directed to the apparent causes of past developments in seeking to perceive the true direction of trends now in existence and effective as bearing upon future developments. The paper will discuss the economics of the Bessemer process, but only to the extent that will bear upon the metallurgist's understanding of his respon-sibility. The problem of the quality of Bes-semer steel will be reviewed and examples will be given of the technical data upon which the reasoning of the paper is based, Matters of engineering design, mechanical maintenance, operation and metallurgical investigation will be surveyed. Compari-sons will be made between the Bessemer and open-hearth processes for the sake of clear and ready understanding,

Jan 1, 1940

Discussion of a paper of S. S. Rummy and W. F. SCHWEDES, presented at the Pittsburgh meeting, October, 1914, and printed in Bulletin No. 94, October, 1914, pp. 2613 to 2635. K. A. PAULY, Schenectady, N. Y.-I have seen this installation and I wish all those interested in the question of electricity as a mine pumping agent could see it. It is not only a model for mine installation, but might well serve as a model for any electrically driven pumping plant. I think I am correct in saying that the pumps are the largest electrically operated centrifugal pumps in mine service in America. I talked with Mr. Rumsey in Duluth just before coming here, and he told me that the actual tests of the equipment as installed checked very closely with the shop tests; that the water delivered by the pumps was slightly in excess of the guarantee, something like 3 or 4 per cent., and that no troubles except of a very minor nature had been experienced with the installation from the start. One point which has been brought out by Mr. Rumsey, and by others who have looked into this question, is the marked saving which' can be made by the application of electricity to pumps, especially to the main sump pumps. The pumps are always located a long distance from the boiler plant and the losses in the steam mains are large. While many of the steam pumps are of a very high grade, yet the tests seemed to indicate that the steam consumption is extremely large. The reduction in operating cost of one small installation which I. have in mind pumping against a head of approximately 2,000 ft.-which by the way was a reciprocating pump-reduced the pumping cost to the neighborhood of one-fifth of the previous steam cost. . The high steam cost was probably due to leakage in the engine and the loss in transmission in the mine, the pumps being located almost half a, mile from the boiler plant.

Jan 4, 1915

Modern, mechanized coal mine ranks with largest in the West - plays major part in CF&I's broad expansion program

Jan 11, 1953

By Norman Weiss

The need for more efficient utilization of labor in the metal-mining industry has been the subject of several recent editorials in the mining press, and one attractive possibility for such improvement lies in the designing of future milling plants particularly with economy of manpower in mind. We are accustomed to think of mill design as the selection and coordinated arrangement of process equipment, but if labor is to be efficiently utilized it must be given early consideration in planning the new mill. There are three good reasons for economizing in labor: (I) to reduce costs, not only in the form of wages but also in housing, hospital, welfare, and other obligations that a company accepts when a new man is added to the payroll; (2) to prepare for recurrent periods of manpower shortage, during which a well-designed plant can manage to get along with skeleton crews; (3) because a milling plant that must depend upon an inordinately large labor force for its operation and maintenance is certain to be inefficient in other respects, for many of the shortcomings in design that make necessary the excessive use of labor are generally not corrected merely by having too many men. A simple example of this is a poorly designed ore-feeding system : if this is inadequate to the extent that one man must be constantly unclogging feed chutes, it may help the situation to put two men or three at this task instead of one, but the feed rate will still be inconstant. First of the factors that affect labor saving is the location of the mill. This is often determined by transportation costs alone, and as a result the mill may be placed close to the mine regardless of the nature of the terrain. The designer must then adapt his layout to the conditions, favorable or not. This happens often at small properties, where capital investment may seem more important than operating expense. In most instances, however, a mill site carefully selected for the advantages it gives the designer in laying out the plant is the most economical in the long run, even if it involves a slight increase in cost of ore haulage. Given some freedom of choice, the design engineer may be able to find just the piece of ground that provides the proper gradient for the needs of the flowsheet, permits installation of essential yards and trackage, and perhaps supplies an excellent site for a tailing dam. Further justification for having placed the mill not too close to the mine sometimes emerges only years later as an opportunity to treat ores from other properties. When it is known from the beginning that the new mill will serve a number of scattered mines, a free choice of mill site is naturally stimulated. The most important single factor in limiting the labor requirements of a mill is its materials-handling system for bring-

Jan 1, 1947

By W. F. Holbrook, T. L. Joseph

The problem of sulfur control is important in all blast-furnace operations but particularly for certain grades of steel because of the rigorous specifications. During the past decade the tendency has been to produce pig iron and hot metal of lower sulfur content. As most of the sulfur in the iron originates in the fuel, the use of high-sulfur coke demands modifications in practice to meet sulfur specifications. While it is generally known that high temperatures and more basic slags favor desulfurization, operators as a rule produce the most acid slag that will permit proper desulfurization. The viscosity of blastfurnace slag has been thought to be related to desulfurization and has been investigated by Feild and Roysterl, also McCaffery and his associates*, but apparently no systematic effort has been made to determine the relative desulfurizing powers of slags over the range of composition encountered in practice. Development of Testing Method Because slag and metallic iron are immiscible, the desulfurization reaction is heterogeneous, occurring only at the interfaces between slag and metal bodies. In the blast furnace the newly reduced iron, containing FeS, descends through the slag bath probably either as small drops or streams, at the interfaces of which desulfurization occurs. After its descent through the slag the iron collects to form a bath of metal, at the top surface of which desulfurization reaction probably occurs. These two steps have been thought to account for all desulfurization in the blast furnace. Kinney3 found that metal removed from the blast furnace just above the tuyeres contained three to four times as much sulfur as the iron at cast. Herty and Gaines4 conclude that most of the sulfur is removed while the metal is passing through the slag. Mund, Stoecker

Jan 1, 1936

By Jasper L. Stuckey

It is not known when kaolin mining was first begun in North carolina, Evidence, in the form of excavations and primitive tools, indicates that some of the deposits were worked in prehistoric times. It has been suggested that the prehistoric mining was for mica, but the workings were all in altered or partly altered pegmatite material and the dumps do not represent the amount of material removed. some of the early openings may have been made in search of kaolin or semi-kaolinized feldspar which was sold to English1 traders along the coast and used in some Of the early English porcelains. In 1744,2 an application was made for an English patent to produce porcelain from an earthy mixture obtained from the Cherokee Nation in North America. It is well established, however, that the occurrence of kaolin in western North Carolina was known in England by 1767. In that year, Josiah Wedgewood sent T. Griffiths3,4 to what is now Macon County, North Carolina, to secure a supply Of kaolin for use in England. Griffiths diary, now in Etruria Museum, Stokes-on-Trent, contains a most interesting account of his experience. Kaolin was discovered at St. Austell, England, shortly after the voyage Of Griffiths, which probably accounts for the lack of further interest in American kaolin. Between 1767 and 1888, there are no records of kaolin mining in North Carolina. In the latter year, however, mining was begun near Webster, Jackson County, and, in the intervening period, has become an important industry. 'Or some 20 years, kaolin mining was carried On chiefly in Jackson, Macon, and Swain Counties. About 1904, it was begun in the Spruce Pine district and for the past 20 Yea's most of the kaolin mined in the State has come from Avery, Mitchell, and Yancey Counties. Distribution The kaolins of North Carolina are limited in occurrence to the Piedmont Plateau and Appalachian Mountain area of the State. While kaolins are widespread in the Piedmont Plateau, having been prospected for in Rutherford, Cleveland, Gaston, Granville, Lincoln, Catawba, Ire-dell, Richmond, Moore, Randolph, and Montgomery Counties, the production from that area has never been important. The known deposits of commercial importance are limited entirely to the mountain area of the State. While kaolins occur widely distributed throughout the mountain area and have been prospected for in many counties of that area, commercial production has come chiefly from two districts. One of these includes Jackson, Macon, Swain, and Haywood Counties. The other includes Avery, Mitchell, and Yancey Counties. Geology With few exceptions, all the known kaolin deposits in North Carolina contain

Jan 1, 1948

By Stuart H. Ingram

The term lightweight aggregate implies material which may be substituted for the usual rock, sand and gravel commonly used as the major part of concrete, but distinguished by being much lighter in weight. Background The art of making and using concrete is old and well developed. Research and experience have pretty well determined the qualities necessary in its constituents, and time has tested theories and applications. Elaborate specifications and tests have been devised and generally adopted governing all phases of concrete work, from selection of material, through engineering design and down to mixing and placing. Standard practices have become routine to executives and laborers, and operations have been simplified and costs lowered. Though many lightweight aggregates meet the basic specifications necessary for usefulness, their physical qualities are so different that they fiequently will not pass standard tests, and some of them cannot be mixed and placed with the usual formulas for water and slump. As a rule their use produces a concrete with a lower modulus of elasticity which requires design change, and being produced in much smaller quantities than ordinary aggregate, production costs are higher. This latter works in a vicious circle to restrict their use and maintain prices that are not competitive, except as against each other. Increased Demand In spite of such handicaps consumption has grown steadily for the past two decades and is apparently growing even faster today. It is evident that lightweight concrete must have better qualities, and be sufficiently better to Overcome the higher cost and the other difficulties and disadvantages pertinent to the use of a new and different material in an old industry. Hence the study of its main ingredient should be of interest to all engineers. Our group has a double interest in the subject since most of the materials which have been used as sources of lightweight aggregate are either mined, Or are by-products of mining operations. We are directly interested in their production as well as their use, and since available supplies of materials suitable are limited, the increasing use, and rising demand, make the discovery of new Or or the development of processes to adapt other natural materials to this use, a promising field; and one in which our profession should take an active part. Recent Development Descriptions of ancient work contain references to the use of spalls of tuffs Or pumice in concrete masonry, but it is only since the nineteen twenties that serious attempts have been made to produce and market lightweight aggregates. A period of rapid advance in theory and practice in cements, mortars and con-

Jan 1, 1948

By Norman Weiss

The need for more efficient utilization of labor in the metal-mining industry has been the subject of several recent editorials in the mining press, and one attractive possibility for such improvement lies in the designing of future milling plants particularly with economy of manpower in mind. We are accustomed to think of mill design as the selection and coordinated arrangement of process equipment, but if labor is to be efficiently utilized it must be given early consideration in planning the new mill. There are three good reasons for economizing in labor: (I) to reduce costs, not only in the form of wages but also in housing, hospital, welfare, and other obligations that a company accepts when a new man is added to the payroll; (2) to prepare for recurrent periods of manpower shortage, during which a well-designed plant can manage to get along with skeleton crews; (3) because a milling plant that must depend upon an inordinately large labor force for its operation and maintenance is certain to be inefficient in other respects, for many of the shortcomings in design that make necessary the excessive use of labor are generally not corrected merely by having too many men. A simple example of this is a poorly designed ore-feeding system : if this is inadequate to the extent that one man must be constantly unclogging feed chutes, it may help the situation to put two men or three at this task instead of one, but the feed rate will still be inconstant. First of the factors that affect labor saving is the location of the mill. This is often determined by transportation costs alone, and as a result the mill may be placed close to the mine regardless of the nature of the terrain. The designer must then adapt his layout to the conditions, favorable or not. This happens often at small properties, where capital investment may seem more important than operating expense. In most instances, however, a mill site carefully selected for the advantages it gives the designer in laying out the plant is the most economical in the long run, even if it involves a slight increase in cost of ore haulage. Given some freedom of choice, the design engineer may be able to find just the piece of ground that provides the proper gradient for the needs of the flowsheet, permits installation of essential yards and trackage, and perhaps supplies an excellent site for a tailing dam. Further justification for having placed the mill not too close to the mine sometimes emerges only years later as an opportunity to treat ores from other properties. When it is known from the beginning that the new mill will serve a number of scattered mines, a free choice of mill site is naturally stimulated. The most important single factor in limiting the labor requirements of a mill is its materials-handling system for bring-

Jan 1, 1947

By C. E. Wood, E. P. Barrett, T. L. Joseph

The United States Bureau of Mines has been studying the blastfurnace process for about ten years. An experimental furnace was developed by the Burcau in cooperation with the Minnesota School of Mines Experiment Station, University of Minnesota. Many data have been obtained and published.' Royster, Joseph and Kinney §(48) found that the particle size of ore had an important effect upon the blast-furnace process. Kinne(28) stated: Economy in blast-furnace practice depends largely upon efficient gas-solid contact in the shaft of the furnace. If efficient work is not done in the shaft, the hearth and bosh will not function properly. A condition may be readily imagined where the particles of ore in the shaft are so large that the time entailed in the descent of these materials into the bosh is not sufficient to permit proper reduction and preparation prior to the time the ore enters the bosh of the furnace. Another condition may be pictured where the density of theatock column and the flow of stock is such that the ore will take one course and the gas another. Both of these examples will result in insufficient contact between the gas and the ore. Unreduced ore will reach the hearth, and the gas which has not been efficiently oxidized will reach the stock line. The result is the use of an excess of carbon in the smelting process. It is obvious that fine ore particles occurring in the ore as charged, or formed in the furnace due to heat and mechanical action, place a definite limitation upon the efficiency of the operation. There is also an economic loss of fine material as dust. Effect of Size of Material Kinney reported (p. 83(29)) the reduction of iron oxides between planes at three furnaces as given in Table 1. The Chicago furnace was operated on Lake ores. Distribution of gas was not good and much of the charge passed into the hearth before the iron oxide was reduced. The Holt furnace was operated on coarse ore. Distribution of gas was fairly uni-

Jan 1, 1930

By W. F. Holbrook, T. L. Joseph

The problem of sulfur control is important in all blast-furnace operations but particularly for certain grades of steel because of the rigorous specifications. During the past decade the tendency has been to produce pig iron and hot metal of lower sulfur content. As most of the sulfur in the iron originates in the fuel, the use of high-sulfur coke demands modifications in practice to meet sulfur specifications. While it is generally known that high temperatures and more basic slags favor desulfurization, operators as a rule produce the most acid slag that will permit proper desulfurization. The viscosity of blastfurnace slag has been thought to be related to desulfurization and has been investigated by Feild and Roysterl, also McCaffery and his associates*, but apparently no systematic effort has been made to determine the relative desulfurizing powers of slags over the range of composition encountered in practice. Development of Testing Method Because slag and metallic iron are immiscible, the desulfurization reaction is heterogeneous, occurring only at the interfaces between slag and metal bodies. In the blast furnace the newly reduced iron, containing FeS, descends through the slag bath probably either as small drops or streams, at the interfaces of which desulfurization occurs. After its descent through the slag the iron collects to form a bath of metal, at the top surface of which desulfurization reaction probably occurs. These two steps have been thought to account for all desulfurization in the blast furnace. Kinney3 found that metal removed from the blast furnace just above the tuyeres contained three to four times as much sulfur as the iron at cast. Herty and Gaines4 conclude that most of the sulfur is removed while the metal is passing through the slag. Mund, Stoecker

Jan 1, 1936

By D. J. McAdam, G. W. Geil, D. H. Woodard, W. D. Jenkins

.In a series of papers, the authors and their associates have shown that the resistance of a metal to fracture is a function of all three principal stresses. Consequently since a technical cohesion limit is defined as the technically deter-minable resistance to fracture under a specific stress system, the technical cohesive strength comprises an infinite number of technical cohesion limits corresponding to the infinite number of possible combinations of the principal stresses. As shown in the previous papers, the technical cohesive strength increases with plastic deformation, with decrease in temperature, and with increase in the strain rate. The technical cohesion limit, therefore, is affected by the same factors that affect the flow stress,$ namely, the stress system, plastic deformation, temperature, and the strain rate. The effect of each of these factors on the fracture stress is qualitatively the same as its effect on the flow stress. The effect of any of the factors may be represented by a curve of cohesion limits, although only one point on the curve may represent actual fracture. Since the term "fracture stress" has come into general use with the same significance as technical cohesion limit, the authors are here using the shorter term with the understanding that it does not always refer to actual fracture. In the general investigation described in the previously-mentioned papers, 10-18,20,21,23 the influence of the stress system on the fracture stress was studied by means of tension tests of notched specimens. When a circumferentially notched cylindrical specimen is subjected to longitudinal tension, the minimum cross section is under transverse radial tension. The mean radial stress increases with the depth and sharpness of the notch, but is always less than the longitudinal stress. The greatest principal stress (S1), therefore, is longitudinal, and since the radial stress is effectively equal to the circumferential stress, the transverse principal stresses are equiaxial in that plane (Sz = S3). By the use of notched specimens in tension tests it was shown that the fracture stress increases with increase in the radial stress ratio (s3/s1) The evidence is based not only on the results of tests to fracture at various constant temperatures, but also On results of two-stage tests, in which each specimen was plastically deformed a predetermined

Jan 1, 1949

By Richard W. Smith

KYANITE, long known to occur in Georgia, did not excite commercial interest until about 1930. Investigations revealed two main types of deposits: (1) separate kyanite crystals embedded in mica schist; and (2) crystal aggregates of kyanite associated with quartz in small and very irregular veins. The second kind at first sight appeared to be the best source of supply. Large boulders or dornicks of kyanite with more or less quartz were found on the surface at many places throughout the Piedmont and Highland sections of the state, but prospecting failed to disclose a sizable vein. These dornicks seem to be a surface accumula-tion from small veins or lens-shaped masses not more than one or two feet thick, and with a horizontal extent of not' more than a few feet. The larger surface accumulation of kyanite dornicks, where not too badly stained by iron oxide, may prove to be marketable, but it is extremely doubtful whether a vein large enough to mine will ever be found. In 1932 deposits of the kyanite-mica schist were known to occur in two places northwest of Clarkesville, in Habersham County. In 1934, at the request of and in cooperation with the Georgia Geological Survey, the United States Geological Survey made a thorough investigation2 of the deposits and found that the two known areas of kyanite-mica schist in Habersham County were but a part of an unsymmetrical, U-shaped belt (Fig. 1) with a western limb extending into Rabun County and somewhat longer than the eastern limb. The total length of the belt is about 30 miles. The width of outcrop ranges from 100 ft. to 1/4 mile or more. Deposits of kyanite-mica schist of very doubtful commercial importance were found in several other counties. Only the deposits of this kyanite-mica schist belt in Habersham and Rabun counties will be discussed in this paper.

Jan 1, 1936

By Jr. J. L. Ryon.

Experimentation with ammonium nitrate-fuel oil mixtures at three underground salt mines revealed its excellent applications at those properties. The author relates the present blasting practice used at these mines by the Intemzational Salt Co. The International Salt Company is presently performing blasting operations with a pneumatically -placed ammonium nitrate-fuel oil mixture at three rock salt mines, and plans its use in the near future at its new Cleveland mine. Use of ammonium nitrate is saving the company approximately $250,000 annually. With rapidly increasing operating expenses and increasing competitive pressure resulting in lower prices, savings such as those realized through the use of ammonium nitrate are vitally important. ORIGINAL INVESTIGATION AND EXPERIMENTAL ACTIVITIES The three mines presently involved are located at Detroit, Mich.; Avery Island, La.; and Retsof, N. Y. Initial experiments were conducted at the Detroit mine where a detailed investigation was carried on to determine the significance of the static electricity factor when blowing ammonium nitrate into drill holes in which millisecond delay electric blasting caps had been placed. Although the information developed at the Detroit mine was passed along to the other mines, each mine independently pursued its own course of inves- tigation. This fact, plus the differing mining conditions, resulted in slightly different operational procedures at each mine. Some of the varying statistical data are shown in Table I, and data common to all three International Salt Company mines are shown in Table 11. BLASTING PROCEDURE AT THE DETROIT MINE This mine has been using the ammonium nitrate-fuel oil mixture for more than two years on a full time production basis and represents the successful detonation of several hundred thousand holes. Results have been excellent and the blasting cost has been reduced many times. The actual operation at Detroit consists of adding the fuel oil to the bags of ammonium nitrate by means of a portable fuel oil tank complete with hose, nozzle, and metering device. The bags of the ammonium nitrate-fuel oil mixture are transported to the working face from the oiling area by means of a jeep-drawn trailer. At the face, the ammonium nitrate is placed on the elevating platform of a powder-load ing rig which consists of a pneumatically-tired, large fork-lift truck with a fully insulated elevating platform constructed on the forks. The placement of the dynamite primer and the pneumatic placement of the ammonium nitrate is a two-man operation. First, one cartridge of the primer is placed in each hole on the line of holes which can be reached from the loading rig platform. The plastic hose is then inserted into the hole and pushes the primer to the back of the hole. The proper charge of ammonium nitrate is then placed in the pneumatic placement machine and,

Jan 1, 1961

By Jasper L. Stuckey

It is not known when kaolin mining was first begun in North carolina, Evidence, in the form of excavations and primitive tools, indicates that some of the deposits were worked in prehistoric times. It has been suggested that the prehistoric mining was for mica, but the workings were all in altered or partly altered pegmatite material and the dumps do not represent the amount of material removed. some of the early openings may have been made in search of kaolin or semi-kaolinized feldspar which was sold to English1 traders along the coast and used in some Of the early English porcelains. In 1744,2 an application was made for an English patent to produce porcelain from an earthy mixture obtained from the Cherokee Nation in North America. It is well established, however, that the occurrence of kaolin in western North Carolina was known in England by 1767. In that year, Josiah Wedgewood sent T. Griffiths3,4 to what is now Macon County, North Carolina, to secure a supply Of kaolin for use in England. Griffiths diary, now in Etruria Museum, Stokes-on-Trent, contains a most interesting account of his experience. Kaolin was discovered at St. Austell, England, shortly after the voyage Of Griffiths, which probably accounts for the lack of further interest in American kaolin. Between 1767 and 1888, there are no records of kaolin mining in North Carolina. In the latter year, however, mining was begun near Webster, Jackson County, and, in the intervening period, has become an important industry. 'Or some 20 years, kaolin mining was carried On chiefly in Jackson, Macon, and Swain Counties. About 1904, it was begun in the Spruce Pine district and for the past 20 Yea's most of the kaolin mined in the State has come from Avery, Mitchell, and Yancey Counties. Distribution The kaolins of North Carolina are limited in occurrence to the Piedmont Plateau and Appalachian Mountain area of the State. While kaolins are widespread in the Piedmont Plateau, having been prospected for in Rutherford, Cleveland, Gaston, Granville, Lincoln, Catawba, Ire-dell, Richmond, Moore, Randolph, and Montgomery Counties, the production from that area has never been important. The known deposits of commercial importance are limited entirely to the mountain area of the State. While kaolins occur widely distributed throughout the mountain area and have been prospected for in many counties of that area, commercial production has come chiefly from two districts. One of these includes Jackson, Macon, Swain, and Haywood Counties. The other includes Avery, Mitchell, and Yancey Counties. Geology With few exceptions, all the known kaolin deposits in North Carolina contain

Jan 1, 1948