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By F. R. Hensel

PuRe silver and silver-lead alloys have been studied as to their suitability for bearing~.' A review of the properties of thallium and the silver-thallium constitutional diagram was made by the author to analyze the possibilities of silver-thallium compositions for antifriction materia1s. t The silver-rich end of the diagram as reported in the literatureg-" was found to be sketchy and it was necessary to carry out corisiderable experimental work to arrive at definite conclusions. Some of the results of this work are reported in this paper. Test Materials In the beginning of the work, only fused alloys were investigated. Later, research Table i.—Composition of Fused Silver-thallium Alloys Tested for Antifriction Properties Percentage Alloy No. of Thallium 1533...................... 0.48 1534.................... 1.06 a31 HT................... 2.04 231....................... 2.10 232 HT................... 3.83 Balance 232....................... 4.07 Silver 233 HT................... 5.86 a33....................... 6.38 a34....................... 9.84 a34 HT................... 10.07 was carried out on electroplating methods and diffusion processes. In preparing the fused alloyst care was taken to exhaust the toxic fumes caused by the thaillium content. The compositions of the series of fused alloys are listed in Table I. The silver-thallium alloys were melted in clay-graphite crucibles and cast into preheated steel molds of 3/4-in, diameter. In the cast condition, they showed a cored structure, as indicated by the micrographs of Figs. I to 3. The etching reagent used was a mixture of 2 grams K2Cr207, 8 C.C. H2S04, and IOO C.C. H20. The cored structure is unsatisfactory for the type of corrosion resistance required for bearing applications, and homogenizing experiments were carried out at various temperatures, the results of which are shown in Figs. 4 through 8. The alloys with a lower thallium concentration, which were heated for 2 hr. at 525°C show an almost completely homogenized solid solution type of structure. With higher thallium concentration, the homogenizing temperature was dropped to 475OC. to eliminate the formation of a liquid phase. It is evident that heating for 2 hr. at this temperature did not iesiilt iii complete elimination of the cored structure. As would be expected, cold-working of the cast structure is an expedient in establishing equilibrium conditions. The fine homogeneous grain structure shown in Fig. 7 corresponds to the cold-worked area under the Rockwell ball penetration when the hardness was taken before heat-treatment. A detailed structural study was made on a cast silver-thallium alloy containing 3.67 per cent thallium. Three micrographs (Figs. 9, 10 and 11) show the transition

Jan 1, 1946

By J. T. Crawford

ALTHOUGH nearly 10 pct of the total tonnage of coal produced annually within the United States is handled by bulk freighters on the Great Lakes, very little of the detail connected with it has been published other than occasional newspaper stories and publication of tonnage statistics. Of the total tonnage floated on the Lakes each year some 10,000,000 is stored and distributed from the port of Duluth Superior, at the western end of Lake Superior commonly known as the Head of the Lakes. This port has the largest single area concentration of coal docks in the world. Since this area contains the largest ore docks, the largest movable material handling bridge, the largest and highest grain elevator and the largest coal briquetting plant in the world, it is entirely fitting and proper that here also should be located the largest coal dock and what we believe to be the worlds largest clam shell. Of the sixteen coal docks operated by ten companies, five are owned and operated by the North Western-Hanna Fuel Co. which has two docks on the Superior, Wis. water-front and three docks in Duluth, Minn. It is with these five docks that we are primarily concerned. GENERAL HISTORY In the summer of 1871 a small sailing vessel entered the harbor of Duluth Superior with the first commercial coal cargo. All the coal brought up that first year did not amount to more than 3000 tons. During the year 1877 the first dock equipped for handling coal was built in Duluth. Coal receipts increased to 52,785 tons in 1879 the first year for which an official record was kept. Since then the volume of water-borne coal to the Head of the Lakes steadily increased to a maximum of 12,688,321 tons in the year 1923. This tonnage was nearly equalled in the year 1927 and the next highest tonnage recent year was in 1946 when 10,105,703 tons were unloaded. The average annual bring-up over a ten year period 1938 to 1947 was 8,605,231 tons. Approximately 30 pct of the coal unloaded at the Head of the Lakes is handled over the docks of the North Western-Hanna Fuel Co. Competition of other fuels coupled with expansion of coal fields in the mid-west have held coal receipts for Duluth-Superior at a relatively constant figure during the last eight years although the total tonnage of coal floated on the Great Lakes has more than doubled in the past 25 years. From the shovel and wheelbarrow method of unloading early cargoes to the horsepowered windlass derrick with a wooden tub was but a short step. The first movable coal handling, steam operated,

Jan 1, 1948

By A. Long, A. Silverman, J. L. Kulp

Garth Crosby has written an excellent geologic description of the deposits surrounding the Gem stocks in the Coeur d'Alene district. The ore deposits in the area of the Gem stocks may hold the key to the age and mineralization history of the entire Coeur d'Alene district. A recent isotopic study10 of the Coeur d'Alene district in this laboratory illustrates that a classical geologic interpretation of these deposits, with its implications for the whole district, may lead to erroneous conclusions. For this reason it seems pertinent to submit a summary of these results and an interpretation of the mineralizing history of the Coeur d'Alene districts. Pitchblende from the Sunshine mine has been dated as 1100-1200 million years (m.y.) by Kerr and Kulp,11 and Eckelmann and Kulp.12 This pitchblende is known to predate the major sulphide introduction in the Sunshine mine, but it clearly follows the metamorphism and folding of the Belt Series. Recently, Goldich (personal communication) dated sericite from the Belt rocks as 1200 m.y. by the potassium-argon method. This date establishes a minimum Belt age if the sericite is of metamorphic origin and a maximum age if detrital. The Belt Series, therefore, is not latest Precambrian. Lead isotope ratios of galenas have been measured and model ages calculated by Bate, et all3 for the Sunshine mine, Farquhar and Cummingl4 or the Bunker Hill and Sullivan mine, and Cannonl6,18 for a few other deposits in the district. Galenas from similar deposits in Southern British Columbia have been measured by Bate, et al,23 Farquhar and Gumming,11 and Wanless and Leech." The new work in this laboratory includes leads from ten widely scattered mines north and south of the Osburn fault, and through a vertical distance of over 5000 ft (Star mine). Included in this group are the Hercules, Sunset, and Mountain Goat mines, which are adjacent to the Gem stocks. In addition, galenas from stringers which cut the Gem stocks in the Success and Sunrise mines and the Hercules hanging wall dike in the lower western portion of the Hercules mine, were included in the study. All of the above leads, except one, give model ages of 1300-1400 m.y. for the time of segregation from the parent material. The concordance of the common lead and U-Pb ages, the great horizontal and vertical uniformity of the lead ratios, the sulphur ratios of two Sunshine mine galenas and three galenas from the Edith, Page, and Hercules mines indicating average crustal sulphur, and the U23/Pb204 ratio inferred for the original lead environment, indicate that the entire mineralization of the Coeur d'Alene-British Columbia base metal belt was derived from a deep source and emplaced in the Precambrian. One sample of galena from sulphide stringers cutting the North Gem stock at the Sunrise Prospect mine gave a modern (i.e., Tertiary) lead ratio. This mine is located at the northern tip of the stock. The presence of modern lead suggests mobilization of some rock lead during the intrusion of the Gem stocks and their outliers. Larsen et al.l8 have dated the Gem stocks as Tertiary by the lead alpha method. If Coeur d'Alene mineralization was genetically related to Tertiary magma formation and intrusion

Jan 1, 1961

By O. E. Palasvirta

Close examination of most so-called n.eu processes in mineral dressing reveals that they were conceived and developed a long time ago. High-intensity magnetic separation is no exception. Although its application in iron ore beneficiation seems new, in Germany the process has been commercially successful for almost two decades. High-intensity separators have long been standard equipment in the glass sand industry; they have also been used in concentrating some of the more unusual para-magnetic minerals. The basic features of an induced-rotor, high-intensity magnetic separator were described by Desire Korda in Paris in 1905,' and many patents have since been issued for improvements on the original design. Fig. 1 shows the basic design of an induced-rotor separator. Several U. S. manufacturers have been supplying induced-rotor separators for many years, but these are all devices of relatively low capacity, not suitable for treating such low-cost commodities as iron ore. On the other hand, two German manufacturers are offering induced-rotor separators of high capacity, both proven in the field. The present investigation was prompted by the apparent success of the German installations and by the discovery of iron ores on this continent which may be amenable to high-intensity separation. The objective was to gain better insight into the underlying principles of separation in a high-intensity field and to use this knowledge in selecting or designing an optimum separator. THEORETICAL CONSIDERATIONS he well known low-intensity magnetic separators are. without exception, of the the magnet type with more or less similar field shapes. It is therefore permissible to speak of their comparative strengths in terms of field intensity alone. However, proper understanding of the high-intensity magnetic separation process requires somewhat deeper analysis of the relationship between the magnetic field and the attractive force. Contrary to a widely held belief, a magnetic field of parallel lines of flux exerts no attractive force on a magnetically susceptible particle, but merely aligns its poles parallel to the lines of flux. On the other hand, a non-uniform field attracts a magnetically susceptible particle in the direction of the converging lines of flux. Thus the force of magnetic attraction varies as the product of the field intensity and the field gradient: dH ds As the induced-rotor magnetic separator is primarily intended for separating feebly magnetic materials, it is important that maximum attraction be attained. For the designer, then, the relationship between the magnetic field and the attractive force has the following implications: 1) Insofar as possible, the separation gap must be saturated with flux. 2) The rotor surface must be shaped to insure maximum convergence of lines of flux toward the rotor. 3) The primary pole face (opposite the rotor, on the other side of the separation gap) must be shaped so that the lines of flux do not diverge from it at any location in the effective separation zone. The actual attractive force of the rotor, and its critical speed, can be calculated as shown by Runo-linna, provided that the true flux density, the field gradient, and the magnetic susceptibility of the mineral can be measured with sufficient accuracy. The irregular shape of the rotor surface makes flux measurements difficult, but it can be done if a suitable gaussmeter is available (see Fig. 2). Calculations by the author, and comparisons with the centrifugal force exerted by the rotor, indicate that the force pinning a hematite particle to the rotor is of the same order of magnitude as the force holding a

Jan 1, 1960

By M. H. Pilkuhn, H. Rupprecht

p layers on n-type substrates of GaAs were prepared by difhsion of zinc into these substrates. Experimental details about the diffusion technique will be presented. It will be shown that inhomogeneity in the substrate doping level and crystal shucture defects cause nonplanarity in the junction plane. These nonplanarities give rise to high threshold current densities. From incremental sheet-conductivity measurements the zinc profile is derived. Data about surface concentration and gradient of the zinc concentration at the junction are presented. Finally, some results of laser diodes, which were made of wafers with extremely planar diffusion fronts, are discussed. ThE investigations reported here are part of a program concerned with the materials aspect in the fabrication of GaAs laser diodes. This includes studies of the influence of crystal defects introduced both during the growth of the crystal and as a consequence of subsequent diffusion. Compared with the progress made in the investigation of structure defects, for instance by X-ray microscopy in materials like silicon, no similar results are known so far for the case of GaAs. The further progress in laser diodes will depend very much upon our knowledge of these structure defects and subsequently upon our ability to avoid them. Laser diodes of GaAs had been made mostly by diffusing an acceptor impurity, normally zinc, into an n-type substrate. This procedure was found more convenient than the inverse one for various technical reasons. We will follow this line and restrict ourselves to zinc diffusion only in this paper. DIFFUSION TECHNIQUES AND EXPERIMENTAL DETAIL In order to set a refgrence for our experiments, we used a standard procedure for the diffusion runs. The diffusions were carried out in a sealed quartz tube for 2-1/2 hr at 850°C. One milligram zinc arsenide (ZnAsz) per cu cm of the tube volume served as zinc source. Under these conditions the junction depth was between 25 and 30 p. It is assumed, according to the investigations of the zinc arsenide system by V. Lyons and V. ilvestri,' that ZnAs2 dissociates completely at 850°C into ZnsAsz and Asg. Since there is a condensed phase of ZnsAs2 in the tube at 850°C, the partial pressure of zinc is controlled by the pressure of the arsenic formed by the dissociation of ZnAs2. Due to the fact that the zinc partial pressure resulting from the dissociation of ZnsAsz is only a weak function of the partial pressure of arsenic, the amount of the initial ZnAs2 is not very critical. Experimentally, we found that the junction depth, as well as the surface concentration, was practically the same, if the ingots of ZnAs2 varied between 0.2 and 5.0 mg per cu cm. The wafers were oriented with the main faces in (100). Surface damage due to cutting and lapping was removed by a chemical-etch treatment in a rotating beaker (etch solution: HzSOr, H202, and HzO in a ratio 3:l:l). The GaAs substrate material was n type and doped with tellurium, selenium, silicon, or germanium. It was grown by means of horizontal or Czochralski techniques. After the diffusion process, junction depth and planarity were checked either by grooving with a

Jan 1, 1964

By L. W. Sink, B. H. Kear, S. M. Copley, M. F. Hornbecker

IT is well known that under appropriate conditions of chill casting, many metals and alloys develop a columnar grain structure having a high degree of preferred orientation.' In cubic materials, this principle has been employed to produce shaped castings with a unidirectional cube oriented columnar grain structure as well as shaped single crystals with a cube axis parallel to the growth ais.' "he purpose of this note is to describe how this same principle can be enlployed to produce wires, rods, or more complex crystal Shapes with a variety of conlpositions in cube or random orientations by a single casting operation. The procedure for directional solidification of in Fig. 2. Examination under crossed polarizers indicated that the striations were a second phase (presumably the B19 phase) which frequently forms initially at primary grain boundaries and then grows toward the interior as thin ribbons. X-ray studies on filings of this alloy reannealed at 1300°C for 15 min indicated a strong pattern of the fcc phase together with a substantial pattern of the B19 phase. The un-annealed filings, however, showed only the pattern of a cold-worked, fcc structure. In these two-phase alloys it appears, therefore, that the B19 phase is transformed into a disordered fcc structure by cold-working. The mechanical properties of these alloys would be of some interest since a fcc structure might be expected to possess greater ductility than the or-thorhombic B19 structure from which it forms. The author wishes to thank Mr. Harvey Yakowitz and Mr. Richard Manuszewski for obtaining the photomicrograph in Fig. 2. This research was partially supported by Research Grant DE-02455 from the National Institute of Dental Research. columnar grained ingots involves pouring a melt into a preheated mold having a water-cooled copper chill at its base? and controlling the temperature gradient in the mold so as to maintain columnar grain growth from end to end of the ingot.4 This is illustrated schematically in Fig. l(a). It should be noted that the longitudinal temperature gradient promoting unidirectional columnar grain growth is maintained by heat loss primarily through the solidifying ingot to the chill, so that both the temperature gradient and the growth rate diminish with increasing distance from the chill. As the distance from the chill increases? the columnar structure coarsens, and the perfection in preferred orientation tends to increase progressively. Using this same procedure of gradient solidification, Fig. l(b) shows a simple scheme for producing a batch of crystals having the same cube orientation rather than an assemblage of columnar grains. Wires and rods are produced by cementing ceramic tubes to the wall of the mold. The steep temperature gradient produced in the central chamber is controlled by the mold heater to produce favorable conditions for crystal growth. Clearly the success of the operation lies in the selection of individual growing columnar grains by some kind of orifice at the base of each channel in the mold. Using simple constrictions, experience with nickel-base alloys has shown that 4 -in.-diam holes at a distance of -1 in. from the chill yield crystals within 7 deg of (100); closer control of orientation is possible by placing the crystal selector farther away from the chill.

Jan 1, 1970

G. D. Kneip, Jr., and J. 0. Betterton, Jr. (Union Carbide & Carbon Corp., Oak Ridge, Tenn.)—The authors have contributed to the theory of zone melting by considering the effects of the solidification of the final zone on the distribution curves for the finite length bar. However, they do not consider in sufficient detail the restrictions imposed by the particular metals involved. Eq. 4 has the analytical solution which is equivalent to Pfann's' equation for normal solidification of the final zone. For distribution coefficients less than one, it is apparent from this form of the equation that, as the solidification approaches completion, the concentration attains extremely large values which are inconsistent with the density of physical materials. The necessary restrictions then are that the solute concentration cannot exceed the density of the alloy, or more frequently, the solubility limit in the solid phase. Secondly, the distribution coefficient cannot be constant from 0 to 100 pet solute unless the liquidus and solidus coincide over this whole region. It would thus be more correct to impose limits on the solubility such as would be indicated by a typical eutectic diagram. Furthermore, in this case the assumption that the distribution coefficient remains constant is more likely to be realized. Eq. 4 should then be replaced by the following C,,(x) =k/L-x [ ?11 3 C11 (x)Ddx - ?11 4 Cn(x)dx= k[Cn (L-l)/k] [ L-x/l]x-1 L-l = x = L-l [kCenterlie/Cn (L-l)]1/k-1 The typical shape for the distribution curve in the final zone is indicated schematically in Fig. 12 for the simple eutectic case. The solidification proceeds according to Pfann's' expression until the concentration reaches the maximum solubility in the solid phasc. At this point, the concentration changes abruptly to the eutectic composition and remains at this value for the duration of the solidification. The width of the flat region, and the back reflection of this effect into the concentration curve on subsequent passes, depends upon the ratio of the eutectic concentration to the original concentration, upon the distribution coefficient, and upon the number of passes. Similar effects on the concentration curves in the first zone length would be expected in many systems for which the distribution coefficient is greater than one, and where the maximum solubility is not too much larger than the original concentration. The discussers agree with the authors that the assumption that the liquid is uniform in concentration should be considered with caution. Kneip and Better-ton' have shown, however, that in floating zone refining of zirconium, using induction heating, the distribution of iron agrees with theory which assumes a uniform liquid composition. Hence, in this case, the experimentally realized distribution coefficient agrees with the present phase diagram within the experimental uncertainty. L. Burris, Jr., C. H. Stockman, and I. G. Dillon (authors' reply)—The authors are happy to have received the comments of G. D. Kneip, Jr., and J. 0. Betterton, Jr., which provide additional insight into the zone refining process. It is true that the equations developed are inapplicable if the solute solubility in the solid phase is exceeded. However, this restriction on the use of the equations was clearly stated in the paper. A closer approach to

Jan 1, 1957

The Goodman Mfg. Co., Chicago, builders of underground electric mining machinery, celebrated its 50th Anniversary on April 23rd. The company has a complete line of cutting machines, loaders, conveyors, locomotives, and shuttle cars for service in both coal and metal mines. The Joy Mfg. Co. has received, under the provisions of the Economic Cooperation Administration, an initial order in excess of $1,000,000 for equipment to be used in the mechanization of iron ore mines in France. While the equipment will be used in various privately owned mines, the order was placed through the French Society for the Development of Mechanical Mining. Included in the equipment are the company's recently developed hard rock loaders and shuttle cars. American Brake Shoe Co. has consolidated all operations of its Canadian subsidiaries into one corporation, the Dominion Brake Shoe Co. Ltd., Montreal, Canada. The products of Dominion Brake Shoe include brake shoes, track equipment, manganese steel castings, automotive brake lining, air compressors, and paint spray equipment. Exhibits of more than 2000 electrical products, processes, and techniques, ranging from precise aircraft instruments to complex working models of steel mill, textile and other industry equipment, will be displayed in the "More Power To America Special" when it makes its nationwide tour this spring. C. H. Lang, Vice-President in charge of sales for General Electric's apparatus department, said that the train will visit the country's key industrial centers for inspection by utility and industrial executives and municipal leaders. The train will be hauled by an Alco¬G-E two-unit, 4000-hp., Diesel-electric locomotive which in itself will be part of the unusual series of displays. Sizing of Excavators and Hauling Equipment. The Power Crane and Shovel Association has released a 24-page bulletin dealing with the proper sizing of excavators and hauling equipment, Technical Bulletin No. 3. Rubber Conveyor Belting. "Installation, Care and Maintenance of Rubber Conveyor Belting" is the title of a booklet just published by the Carlyle Rubber Co., New York. Power Transformers. The manufacturing procedure of Allis-Chalmers small power transformers is described in a new 28-page bulletin, 61B6094A, covering the core and coil unit, no-load tap changer, tank construction, cooling methods, oil preserving systems, bushings, terminal compartments, indicators and testing of transformers. Safety Equipment. General Scientific Equipment Co., Philadelphia, has released a 46-page, fully illustrated catalog on personal protective equipment and industrial safety devices. This new catalog covers respiratory devices, eye protection, hats, gloves, carboy pumps, drum pumps, and miscellaneous safety equipment for use in mines, industries, etc. Osmosalts. The Osmose Wood Preserving Co., Buffalo, N. Y., has issued a bulletin on Osmosalts, the wood preservative which, say the manufacturers, makes timber last three to five times longer, slashes maintenace costs, stops rot, and resists wood-destroying insects. Jigs. The Dorr Co. has acquired the Pan American jigs and they are now known as the Dorrco-Pan American jigs. Originally developed as a gold-saving device for dredges, the simplicity, ease of operation. efficiency, and negligible maintenance of these jigs have resulted in wide adoption on all types of placer operations, in the closed grinding circuits of gold mills, and on many applications where a coarse bed concentrate is separated from the ore gangue.

Jan 5, 1950

By Karl F. Peterson, H. K. Najarian, Robert E. Lund

R. E. Powers (Mellon Institute of Industrial Research, University of Pittsburgh, Pittsburgh)—Several of the processing methods at the Josephtown smelter might well be considered by plants producing iron blast furnace sinter. In making blast furnace sinter the objectives are much the same as at Josephtown: To produce a strong yet porous agglomerate which has a size consist in a preferred range. The emphasis however is on production rate rather than on the size or other quality characteristics of the sinter. Therefore the technique is entirely different. Blast furnace sinter plants attempt to make their product in one pass with a minimum recirculating load and without sizing treatment after the sinter leaves the machines. Many plants are beginning to feel that more attention paid to quality characteristics would make the product a more desirable blast furnace material. The pelletizing of very fine material before placing it on the bed is not deliberately done at iron sinter plants, although the installed equipment sometimes gives a simila; action. Such pelletizing seems to be a promising way of accommodating the down-draft sintering Drocess to very fine materials. he recirculating load at Josephtown is extremely high. Two plants' producing blast furnace sinter from raw material of comparable size have a recirculating load of about 100 pct of production. At Josephtown it is notable that the size and the rate of feeding of return fines are under control. This is not the case in most blast furnace sinter plants. The sinter slicer appears to be a worthwhile aid in effecting such control. It is similar in action to rakes and plows used at a number of plants, but it has the advantage that the sinter dislodged is positively removed and not left to the inefficient action of a stationary grizzly screen. Blast furnace size specifications for sinter are not at present so rigid as the Josephtown specifications. If the sizing of blast furnace sinter does become important, then the Josephtown crushing practice, in which a large recirculating load is maintained on the crusher in order that minimum fines be produced, may be of interest. H. K. Najarian (authors' reply)—We note that Mr. Powers appreciates some points that we tried to emphasize in our paper as being of importance in making zinc sinter of good quality and which may well be applied to iron blast furnace sinter. Fig. 2 shows the pelletized nature of the feed going on to a Dwight-Lloyd type sintering machine in our plant. Practically, the entire feed consists of more or less rounded particles which permit more uniform air passage through the charge, while the larger particles in the charge roll on to the surface of the grate, which helps to keep the grate openings from being clogged by excessive fines. An agglomerated charge of this character may preferably be made by rolling action while being mixed in a rotating drum and wetted by water sprays to bind the fine particles together and give the charge the desired moisture content. From our observations of several iron ore and blast furnace flue dust sintering operations, we believe that if the fines from the sinter discharged from the machines were to be recirculated and agqlomerated with the new feed, not only sinter of better quality but larger capacity from the machines may be realized.

Jan 1, 1952

THERE has been a lot of talk about the shortage of engineers and we have done our share of it; but recently we heard a spot radio commercial-between broadcasts-urging high school seniors to study engineering. We think this is going too far. Engineering is an exacting profession requiring the highest personal qualifications. Publicity for the purpose of interesting capable young people in choosing courses in engineering should emphasize qualification. The opportunities for a career in a great constructive profession which is the basis of our high standard of living should be properly evaluated. Although there is a need for more engineers today, nobody knows what the employment potential is going to be four years hence. The profession may do itself a grave disservice by attempting mass recruitment in the face of an unpredictable national economy. The mining and metals industries are in a special position as fewer engineers are needed in these fields. Only 10 pct of all engineers are mining and metallurgical engineers. Today's shortage is not so much in recent graduates, but in trained practicing engineers. The shortage has served the profession to good effect because it directed the talents of engineers into more productive channels. In some areas high school graduates have been put into routine jobs such as, surveying. If there is one thing the mining profession does not want, it is an oversupply of graduates which would relegate college men to years of work and discouragement in routine jobs. The public has a clear cut picture of the legal and medical professions and thus the respect knowledge imparts. But the engineer is variously thought of as a man who pulls the throttle lever on a locomotive, tends a furnace, or builds a bridge. The term engineer is too loosely used. For instance we have heard of "crowd engineers" and "exterminating engineers." In some unions an engineer designation has been established to describe a person doing routine checking or other control job. We do not disparage these positions but they are different from the work done by the man qualified by years of experience and study. Many of these so-called engineers are not engineers at all. The engineering profession has cooperated closely on a program of recruiting high school graduates for engineering study. It should start a cooperative public relations program to enlighten the public on the accomplishments and work of engineers. This type of publicity need not be of the bombastic type. It can be educational and dignified. Radio, television, and the periodicals can be used to convey information. It is time that laymen and interested young people learn to make a distinction between the true engineer and the technician. Such a program would instruct parents and high school students and thereby interest the right type of people in the engineering profession. The Centennial of Engineering sponsored by the American Society of Civil Engineers is a step in the direction of instructive public relations. This fine start should not be allowed to remain as a one pass venture. The engineering profession as a whole should follow this exposition with a sustained, well directed effort to inform the public of the engineer's work and the possibilities it holds for a constructive career.

Jan 1, 1952

R. E. Powers (Mellon Institute of lndustrial Research, University of Pittsburgh, Pittsburgh)—Several of the processing methods at the Josephtown smelter might well be considered by plants producing iron blast furnace sinter. In making blast furnace sinter the objectives are much the same as at Josephtown: To produce a strong yet porous agglomerate which has a size consist in a preferred range. The emphasis however is on production rate rather than on the size or other quality characteristics of the sinter. Therefore the technique is entirely different. Blast furnace sinter plants attempt to make their product in one pass with a minimum recirculating load and without sizing treatment after the sinter leaves the machines. Many plants are beginning to feel that more attention paid to quality characteristics would make the product a more desirable blast furnace material. The pelletizing of very fine material before placing it on the bed is not deliberately done at iron sinter plants, although the installed equipment sometimes gives a simila; action. Such pelletizing seems to be a promising way of accommodating the down-draft sintering Drocess to very fine materials. he recirculating load at Josephtown is extremely high. Two plants' producing blast furnace sinter from raw material of comparable size have a recirculating load of about 100 pct of production. At Josephtown it is notable that the size and the rate of feeding of return fines are under control. This is not the case in most blast furnace sinter plants. The sinter slicer appears to be a worthwhile aid in effecting such control. It is similar in action to rakes and plows used at a number of plants, but it has the advantage that the sinter dislodged is positively removed and not left to the inefficient action of a stationary grizzly screen. Blast furnace size specifications for sinter are not at present so rigid as the Josephtown specifications. If the sizing of blast furnace sinter does become important, then the Josephtown crushing practice, in which a large recirculating load is maintained on the crusher in order that minimum fines be produced, may be of interest. H. K. Najarian (authors' reply)—We note that Mr. Powers appreciates some points that we tried to emphasize in our paper as being of importance in making zinc sinter of good quality and which may well be applied to iron blast furnace sinter. Fig. 2 shows the pelletized nature of the feed going on to a Dwight-Lloyd type sintering machine in our plant. Practically, the entire feed consists of more ,or less rounded particles which permit more uniform air passage through the charge, while the larger particles in the charge roll on to the surface of the grate, which helps to keep the grate openings from being clogged by excessive fines. An agglomerated charge of this character may preferably be made by rolling action while being mixed in a rotating drum and wetted by water sprays to bind the fine particles together and give the charge the desired moisture content. From our observations of several iron ore and blast furnace flue dust sintering operations, we believe that if the fines from the sinter discharged from the machines were to be recirculated and agqlomerated with the new feed, not only sinter of better quality but larger capacity from the machines may be realized.

Jan 1, 1952

By H. D. Kessler, M. Hansen, R. J. Van Thyne

The phase diagram of the titanium-rich portion of the system Ti-Cr-Fe to 70 pct Ti was established by means of isothermal sections at 900°, 800°, 750°, 700°, 650°, 600°, and 550°C, using arc-cast alloys. An isotherm at 800°C was determined for the section bounded by Ti, TiFe2, and TiCr2. Micrographic analysis was employed as the principal method of investigation, supplemented by X-ray diffraction and incipient melting studies. A ternary eutectoid, ß ? a+ TiCr2 + TiFe, occurs at approximately 8 wt pct Cr, 13 wt pct Fe, and about 540°C. AMONG the first titanium-base alloys in commercial production were the Ti-Cr-Fe alloys. For this reason, the Materials Laboratory, Wright Air Development Center, sponsored an investigation of the system. No information on the constitution of the titanium-rich corner was available. Vogel and Wenderott studied titanium-poor ternary alloys.' As part of this program, the binary systems Ti-Cr and Ti-Fe have been determined previously by the authors.' Other investigators have also studied the binary systems Ti-Cr,3-7' Ti-Fe.³,8-10 Both of the binary systems are characterized by the eutectoid decomposition of the ß phase. Most of the effort of the present work has been concentrated on the titanium-rich corner with compositions of less than 30 pct total chromium and iron content. The determination of isothermal sections was the experimental approach used to obtain the ternary phase diagram. Vertical sections were used to check the consistency of the isothermal sections. While this investigation was in progress, a study of the Ti-Mo-Cr system at Armour Research Foundation disclosed the existence of a high temperature modification of TiCr2 above 1300 °C.11 This allotrope has a hexagonal structure of the MgZn2 type, iso-morphous with TiFe2, whereas the low temperature modification of TiCr2 is cubic," of the MgCu2 type. The existence of allotropy in TiCr2 of course means a more complicated set of phase relationships in this general region than if the phase were monomorphic, as was first assumed. Additional studies were made late in the investigation in order to clarify the part that the hexagonal TiCr2 phase plays in the ternary phase relationships. These will be discussed in a separate section. Because they are of greatest practical significance, the phase relationships in the titanium-rich corner will be presented first, omitting the equilibria involving the hexagonal modification of TiCr2 in an effort to simplify the presentation somewhat. Experimental Procedure Materials: The titanium used in the preparation of the alloys was iodide crystal bar (99.9 pct pure) produced by the New Jersey Zinc Co. High purity chromium and iron were obtained from the National Research Corp. Table I gives the analyses of these materials. Melting Practice: Over 100 alloy ingots weighing 10 to 20 g were melted in a nonconsumable electrode arc-melting furnace. As the techniques are identical to those reported previously,12,13 they will not be detailed here. The ingots were melted in the cavity of a copper melting block insert under a slight positive pressure of helium. No measurable hardness

Jan 1, 1954

By Kenyon E. Richard, James H. Courtright

Thomas W. Mitcham (Strategic Minerals, Inc., Grand Junction, Colo.)—The authors have presented a significant contribution to the field of mining geology. The article is graphic, remarkably concise, and crisply original. The presentation is made on only three pages with two maps, but their Silver Bell story is entirely adequate in background, development, and conclusion. Most of their colleagues would agree that this paper reflects the high quality of the work which these unusually capable men have done in the Silver Bell area over the past few years. The Silver Bell area is one of complex tectonic structure, and time and spatial relationships are by no means apparent. Actually, most of the observations and interpretations in this paper are new to published geologic literature on the Silver Bell area. I am in agreement with these interpretations with two possible exceptions, which are discussed below. One might well define the three roughly parallel west-northwest faults, shown on the insert of Fig. 2, as the major structural elements of the area. North to south, I propose that these be named the Ragged Mountain fault, the Silver Bell fault zone, and the Waterman thrust, after the mountain ranges which are the results of these major structures. While I would agree with the authors that the northern two of these major structures are high-angle faults of the Laramide revolution, my impression is that the southern structure is a low-angle thrust of approximately Miocene age. In support of this opinion, I submit the following observations: 1) irregularity of the fault in strike; 2) scarcity of Laramide intrusives and alteration of sediments along the fault; 3) present high re- lief of the Waterman Range which indicates youth or certainly rejuvenation; and 4) existence of a series of parallel structures farther to the south which results in an outcrop pattern suggesting imbricate thrusting. The authors have stated that Laramide igneous activity began with the intrusion of alaskite. Some dacite flows appear to be conformable with Cretaceous beds, and thus my impression was that alaskite followed the intrusion and extrusion of dacite. I would be interested to learn of evidence in support of the reverse relationship suggested by the authors. Kenyon Richard and J. H. Courtright (authors' reply)—The authors appreciate Mr. Mitcham's attention to this paper. The names he proposed for the major faults seem appropriate. His suggestion that the Waterman fault is a thrust may be correct because he did more work in that particular area than the authors. However, it is believed that no direct evidence of a low-angle thrust relationship has been recognized, and the authors consider that indirect evidence favors a high-angle fault interpretation. The pre-dacite flow age of the alaskite is definitely established, the authors believe, by the fact that the flows rest on an erosion surface which was carved in the dacite porphyry, an intrusive clearly younger than the alaskite, as evidenced by inclusions of alaskite occurring in dacite porphyry. No direct evidence of Cretaceous sediment-flow rock relationships was found at Silver Bell, but in the nearby Tucson mountains dacite agglomerates, megascopically similar to those at Silver Bell, overlie a basal conglomerate which in turn rests on the truncated edges of steep-dipping Cretaceous arkosic beds.

Jan 1, 1956

By -1ng. B. Stampa

Introduction The author investigates the technology available for mine flow reversibility by reversing the operation of the main fans. Air bypassing, reversed sense of impeller rotation, and blade angle overturning are indentified as the most important means of achieving the flow reversibility. The axial flow fan is studied in some detail and the important variables of fan capacity, pressure, and efficiency are compared. Although some references to rotor velocity vectors are made (Fig. 1) the subject is not presented in detail in order to stay within the paper's intent. Background Where applicable, the requirements of mine air reversibility are an important part of the overall mining operation and should be given proper attention during mine ventilation design. The need for preventing mine fires in intake shafts is the reason that, for a long time, it has been a requirement in the Eastern European countries to have the feature of flow reversibility built into all main mine ventilators. In West German coal mines, this requirement does not apply since higher priority is given to safety precautions. Some metal and mineral mines in the United States are required to have ventilation currents readily reversible in order to fight underground fires as stipulated by the Title 30, Mineral Resources, and by the mining laws of some states. From an equipment performance standpoint, assuming the validity of other flow technical data, the question of the ventilator flow reversibility is of ten related to the actual scenario of the begining of an emergency. Most of the time, the system operates within half of the design capacity only and assuming that the equivalent mine orifice is stable only a quarter of the design pressure must be produced by the fan in any event. For such an operating point, the effective gradient and energy losses can be disregarded since fire emergencies usually last for only a short period of time. Equipment Comparison Fig. 2 depicts a ventilation arrangement wherein the flow can be reversed through changing the functional position of the dampers (slideplate or blade type). Both axial or radial fans can be applied in this case. For the mine exhaust operation, slide plates (guillotines) I and I11 are opened while plates I1 and IV are closed. The flow thus encounters two reroutings, which due to the reverse ventilation flow cannot be equipped with proper sheet metal deflectors, and therefore large pressure losses result during the air reroute operation. When the intake operation is considered, the dampers I and I11 are closed and the pair I1 and IV is opened. For this arrangement, almost the same flow conditions exist as for the foregoing exhaust mode; however, one additional corner must be applied. Even if a highly efficient ventilator is used in one of the previously described systems, the additional pressure losses resulting from air rerouting plus those encountered between the planes "0" and "00" significantly affect the overall energy requirements. Illustrated in Table 1 are the relative component losses of even flows for evaluation of various detour arrangements. From the aerodynamics standpoint, when these components are being designed, serious consideration must be given to the individual levels of the pressure loss coefficient, 5. Should there be an increase in the sum of the loss coefficients due to the particular component selection such that, for example, the net change is 1.2; the resulting pressure to be produced by the fan can be calculated from:

Jan 1, 1981

By Herbert Hoover

IT is always a pleasure for me to join in the Ameri-can Mining Congress, for not only has my own professional life been closely linked with the industry, but the Secretary of Commerce is specifically enjoined in the organic act creating the office to promote and foster the interests of the mining industry. And it is a vital part of our national life. It is one of those indus-tries without which. the nation could not go on for a week. It ranks second only to the agricultural industry in its contribution to our raw materials. Its production amounts to nearly 6 ½ billions annually, providing direct support to probably ten millions of our people through employment to about two million workers. But the in-dustry has a greater importance than even these figures indicate, for with agriculture, forestry, and water power it furnishes the raw materials upon which the whole work of our civilization rests. When the raw ma-terials of our mines emerge. from manufacture with the added expenditure of labor and capital upon them, they have a wholesale value of over fifteen billions of dollars. And in this, the second stage of their application, they give employment to another two million workers and support to about ten million more of our people. A large portion of these manufactured commodities must filter through the retail trade; their total value when delivered to the consumer exceeds twenty billions of dollars. And from this distribution arises the support of many more millions of our people. It is estimated that the products of agriculture when they reach . the consumer, with transportation, manu-facturing, and distribution costs added, have about the same value as the mineral industries-each of them thus contributing about one-quarter of our total na-tional income. No other continent has demonstrated its possession of such a magnitude of minerals as has ours, and such a bountiful distribution over our whole land. But our mineral resources differ in one essential from our other natural resources-they are not renewable. Agricul-ture, forests, and water power replenish their supplies from season to season. Some people conclude from the non-renewable character of the mineral supply that they must shortly be exhausted. The practical question is ,one of time, and time in these matters needs to be measured in generations, and apprehension of exhaus-tion needs to be tempered with many probabilities in-cluding the advance in technical methods of extraction. In some of our minerals, such as coal, iron, and building materials we can, through a knowledge of their geologi-cal structure and occurrence, make fairly good estimates of our reserves. We. know that they will outlast many generations of Americans. In non-ferrous metals and oil, geology affords us no great basis for an estimate of future supply. We only know of the occurrence of minerals of this type by actual exposure of them, and we can thus make no estimates except upon reserves which have been proved by actual development by the process of mining. To develop them ahead merely for national satisfaction of assured future supply would imply an unbearable waste of capital. The consequence is that in these groups there is never a demonstrable assurance of more than a few years' supply ahead of us. Yet we have never failed from year to year to find new deposits and extension of old deposits.

Jan 1, 1928

By R. C. Hall

The magnetic anisotropy and magnetostriction of single crystals of alloys between 25 and 59 wt pct Co in Fe have been determined in the disordered and ordered states. The magrzetostriction is large and positive for all alloys in both states of order (up to 150 x 10-6 for A,, and 40 x 10-6 for 111). The magnetic anisotropy becomes zero rzear 41 pct Co for the disordered state. Ordering shifts the zero-anisotropy composition to about 50 pct Co. COBALT-iron alloys have for many years been of interest as magnetic materials because they have unusually high magnetic saturation values.' This interest was increased recently by the development of Supermendur.' Supermendur is an alloy of 49 pct Co-49 pct Fe-2 pct V* which was found by suitable purification and heat treatments, including a magnetic anneal, to possess excellent magnetic properties. These included a square hysteresis loop with a low coercive force and a high magnetization, and a low total loss. Two factors which are important in determining the magnetic hysteresis properties are the basic magnetic properties of magnetostriction and anisotropy. Alloys having zero anisotropy and zero magnetostriction show improved hysteresis properties.3 Since very meager data4-' are available in the literature on the single-crystal anisotropy and magnetostriction of the cobalt-iron alloys, the present program was undertaken to determine these two properties in the disordered and ordered states. EXPERIMENTAL TECHNIQUES Ingots of the cobalt-iron alloys containing from 25 pct to 59 pct Co in iron were vacuum melted from electrolytic iron and cobalt of 99.9 pct purity. The ingots were cooled at a rate of about 1°C per hr through the transformation temperature (950" to 980°C dependent on the alloy content) for the growth of large grains. From these grains, single-crystal disks were fabricated with either the (110) or (100) plane parallel to the faces of the disk. The crystals were given two heat treatments to produce either the ordered state (cooling rate of 20°C per hr from 850 "C) or the disordered state (water quench from 850 °C). Since the iron-cobalt alloys order very rapidly, the water quench may not have produced complete disorder in all cases. Due to the method of growth, the crystals were not perfect. Most of the samples had low-angle boundaries and a few had some small included grains. These imperfections could and probably did affect the accuracy of both the magnetic anisotropy and magnetostriction measurements. Much of the scatter in the data may be attributed to the crystal imperfections. The methods of determining the spontaneous saturation magnetostriction and the anisotropy have been previously described.419110 MAGNETOSTRICTION The magnetostriction in the [loo] and [Ill] directions (hO0 and ?111 respectively) is illustrated in Fig. 1 for the disordered state. Both ?100 and ?111i became large positive values as cobalt was added to iron. The state of order did not have a large effect on the magnetostriction. The effect of order did not appear too consistent in these data. Tentative curves are shown in Fig. 1 for the ordered magnetostriction near the FeCo composition; here ?100 appeared to be lowered and ?111 raised as the degree of order was increased. These results agree qualitatively with the

Jan 1, 1961

By Evert Hoek

Summarising a conference is never an easy task, but I will try to keep my comments brief and to the point. There are a number of lessons which we have learned from our deliberations together during these past three days, and I will try to give you my impressions of these lessons and of their practical implications in open pit mining. The first thing that has become increasingly obvious during these discussions is that it is no longer acceptable to offer an 'Act of God' as an excuse for a major slope or tailings dam failure. Disasters such as that at Aberfan in the United Kingdom have focussed the world's attention on the activities of the mining industry and the report of the commission set up to investigate the Aberfan disaster clearly showed that adequate knowledge was available and that failure to apply this knowledge did not qualify as an 'Act of God'. The courts and the world's press are certain to impose increasingly harsher penalties and criticism on those held responsible for major failures, particularly of tailings dams, in the future. One of the major problems in applying available knowledge to slope problems is that attempts to apply this knowledge are frequently left too late. To provide an engineering solution in the case of a slope in an advanced state of failure is an almost impossible task, and it is essential that those responsible for the stability of a slope must learn to recognise signs of distress at an early enough stage for effective remedial measures to be taken. As our ability to solve slope problems improves, the time at which slope stability problems are considered in a mining project must move forward to a stage at which these problems can be anticipated and dealt with before they arise. Conferences such as this are important in that they enable us to exchange ideas and advance our knowledge to a level at which such predictive engineering will be possible. It has been encouraging to hear of mining projects such as the Bougainville Copper operation where slope stability studies were carried out as part of the overall evaluation programme and it is hoped that this will become a more common procedure in the future. Providing a safe slope in an opencast mine obviously costs money, either in terms of the reduced ore to waste ratio given by flat slopes or because of the cost of stabilization techniques such as drainage or the use of rock anchors. An optimum slope design will provide maximum safety at minimum cost but achieving this optimum is not an easy task. Any one of us could design a slope which would be stable to the end of time, but it is probable that that slope would be so flat as to be totally uneconomic in most open pit mining situations. On the other hand, if the overall economics of a mining project are so critical as to require slope angles which the engineer responsible for these slopes considers to be unsafe, it is his duty to make us could design a slope which would be stable to the end of time, but it is probable that that slope would be so flat as to be totally uneconomic in most open pit mining situations. On the other hand, if the overall economics of a mining project are so critical as to require slope angles which the engineer responsible for these slopes considers to be unsafe, it is his duty to make

Jan 1, 1971

By W. W. Krysko

In order to calculate the critical particle size of lead oxide entrapped in lead, Stoke's Formula may be applied. All data were available except figures for the density of lead oxide at elevated temperatwes. The density of lead oxide was determined by means of dilatometmetrc and volumetric methods up to 1010°C. Graphs of the density of lead and lead oxide as well as the viscosity of lead are given and discussed, with the conclusion that the most unfavorable region for the separation of lead oxide from molten lead lies just above the melting point of lead. DURING previous investigations, particularly on the dedrossing of lead with aluminum1 and the oxygen solubility in lead,' the critical particle size of lead oxide which could be entrapped in solidifying lead was estimated by calculation, and it was shown that high values found for the oxygen content of lead may be due to the method of sampling and the entrapped particles of dross. Unfortunately, due to lack of data, an exact mathematical solution was not possible. The particle size which will separate under a given condition can be estimated from Stoke's Law, which states that where: d = diameter of the critical particle size ¦q = viscosity of lead in Poise V = constant velocity in cm sec-I g = 981 cm sec-2 61= specific gravity of lead 62= specific gravity of lead oxide The depth of the lead bath and the time before solidifying define the velocity. The viscosity of molten lead is known from earlier work by Krysko and is given in Table I. The specific gravity of lead is also known, see Table II. These values are according to Hofmann. A careful survey of literature revealed no values for the density of lead oxide at elevated temperatures. The present investigation was therefore conducted to provide this information. RESEARCH INVESTIGATIONS The density of lead oxide was determined from the following experiments: 1) Determination of the density of lead oxide at room temperature. 2) Dilatometric investigations on the same samples. 3) Determination of the shrinkage at the liquid-solid trans£ormation. 4) Density determinations on liquid lead oxide. 5) Time temperature curves during cooling. 1) The samples for the determination of the density of lead oxide in the solid state were prepared in the following manner. Molten lead oxide was cast into I hot mold which could be opened along the longitudinal (vertical) axis. The cast samples were cylinders of approximately 10 mm diam and approximately 80 mm length. The cylindrical hot mold was open at both ends and was placed on a large copper chill plate shortly before casting. The solidification of the lead oxides proceeded upwards without any formation of internal cavities. The sample was carefully checked with respect to density and crystalline appearance, and only the lower portions which were crystalline and free from porosity were used. The density was determined in a specially made pyknometer-like container, where the surplus liquid was squeezed out through an orifice approximately 1/10 mm in diameter. Mercury or water was used as the liquid. The densities of the samples were calculated from the weight, volume, and mean specific gravity of eight samples was 9.62 * 0.05 g cm"3 at 22"~. 2) The samples were machined to approximately 1 1/2 in. in length and fitted into a dilatometer. A

Jan 1, 1962

By Joseph G. Franzone, Alan K. Kuhn, Jerry J. Oliver

INTRODUCTION Tailings produced by many uranium milling operations consist of fine sands with some silt and slimes. When fine sandy materials are placed by hydraulic methods behind an impermeable dam, they are deposited in a loose state and some portion remains saturated. These saturated, loose fine sands are highly susceptible to liquefaction, the phenomenon in which a monotonic or cyclic disturbance causes excess pore water pressure and, concurrently, a total loss of strength in the sand. Once liquefied, the fine sand flows, causing collapse of supported structures. The potential for such a liquefaction failure was identified and successfully treated at Sohio Western Mining Company's L-Bar Uranium Operations near Seboyeta, New Mexico. The Sohio tailings dam is an earthfill starter dam with tailings raises constructed upstream of the starter dam crest. Beginning with the start of mill operations in 1976, tailings were deposited hydraulically in the impoundment behind the starter dam. As the tailings level approached the crest of the starter dam, beached tailings were excavated and placed in lifts by a dozer to form two raises above the crest of the starter dam. As the impoundment has gradually filled with tailings, the decant water pond level has risen. Correspondingly, the water level in the tailings dam, upstream of the chimney drain, has also risen. By August 1980, the phreatic surface was above the crest of the starter dam and stability analyses indicated that the tailings dam did not have the safety factor of 1.0, under static loading with liquefaction, implicit in the 1980 New Mexico State Engineer's requirements. The problem related directly to the high phreatic surface in the loose sandy tailings behind a dam structure that was not capable of resisting failure which might develop in liquefied tailings. Two methods of stability enhancement were considered for the Sohio dam. One method was reinforcement of the dam using a clay buttress placed against the downstream slope. The other method was installation of horizontal drains through the starter dam to drain decant water and lower the phreatic surface. Either method would increase the stability of the dam. However, the comparative analysis of the methods indicated that horizontal drainage offered significant advantages in cost and could provide a more direct remedy of the source of the problem, the saturated section of tailings. In addition, a drainage system would be more amenable to modification and more quickly installed than a buttress. On the other hand, a clay buttress could be more directly controlled, would involve routine earthwork, and has successful precedent. Therefore, the buttress approach would involve less risk. After weighing the advantages of both methods and the costs versus risks, the horizontal drainage approach was selected. Consequently, a horizontal pipe drain system was recommended and designed (D’Appolonia, 1981a). This paper describes the design and installation of the drainage system and its initial performance. PIPE DRAIN SYSTEM DESIGN Design Criteria and Parameters To increase the stability of the dam to acceptable levels, the drainage system had to lower the phreatic surface behind the dam to the level calculated to give a minimum safety factor of 1.0 under conditions of liquefaction. In addition, the system needed to be essentially self-operating, easy to maintain, and economical. To accomplish these objectives, the following design criteria were established: 1. The pipe drains must lower the phreatic surface at least 4.3 m (14 ft.) at the midpoint along the dam (the deepest section) and by proportionately smaller amounts toward the abutments to satisfy safety factor requirements.

Jan 1, 1982

By W. H. Triplett

DISCUSSION John G. Barry (Mexico)—"The Nerinea limestone," writes W. H. Triplett, p. 584, "is ... medium-bedded (0.5 to 1.0 m)...." This is the Zuloaga formation. It has always been described as thick-bedded (1.0 to 3.0 m). "Whether the marls and shales were less amenable to replacement," he goes on to say, ". . . is a matter of opinion." In general, it is probable that the thinner-bedded formations were less competent than the nearby thicker-bedded, so that the latter produced pre-mineral breccias when all were subjected to flexing stresses. With reference to Mr. Triplett's analysis, p. 584, under Lower Cretaceous, in the Taraises and Cupido formations some few horizons should be considered as possibly containing hidden orebodies. In the Potrero camp, shown on the general map in the northwestern part of Fig. 4, p. 587, several mineralized beds are known; they are found throughout the whole thickness of the Cuesta del Cura formation. With regard to intrusive rocks, p. 585, the general map, Fig. 4, shows that the Potrero and Noche Buena camps are near a third, monzonitic intrusive. It seems doubtful that the Aranzazu was any hotter than the Providencia camp. However, the former does contain large deposits of exogenetic silicates, which in large part occur within the Zuloaga limestone, as shown by Bergeats in a stereogram. At the Aranzazti camp the La Caja formation was only slightly changed, whereas it was altered highly at the Providencia, possibly en-dogenetically. That the temperatures at the Providencia camp were relatively high at one time is also shown by the tourmaline veinlets and lenses in the monzonite and by the garnets on Temeroso peak; high temperature mineralization has possibly been eroded. Maps and sections show that the Concepcion del Oro —Temeroso stock occupies the original locus of some 40 kms of sedimentary rocks. The remains of large roof pendants at Carmen and Animas indicate that stoping was active. Whether all the sedimentaries were stoped and assimilated presents a lively problem, a correlative of which would be an estimate of the original constitution of the invading instrusive rock. As to extrusive rocks, see p. 585, there is also a large thick area of the extrusives left near Noche Buena in the "La Caja" intramontane valley of the La Caja range. This place gave its name to the range. The volcanics are also said to occur in considerable amount in the Mazapil valley.'' Turning now to the remarks under Regional Structure, p. 586, as partly indicated on the general map, Fig. 4, the Mazapil Mountains of the Mazapil region are a continuous, U-shaped range including a northern leg of some 24 km, a southern leg of similar length, and a uniting base which lies to the East and which measures some 10 km in a S 20 E direction. Thus the U-shaped mountains are continuous through a length of 58 km and also contain one continuous anticline, the adjacent valleys being synclinal. The northern leg of the U is called the La Caja range, the base is called the Concepcion del Oro range, and the southern leg the Santa Rosa range. The ranges in northeastern Zacatecas and southern Coahuila contain anticlines and the valleys contain synclines, which where thin are necessarily highly compressed isoclines with very steep dips. Many of the anticlines also have isoclinal components which are overturned, original mushroom tops being indicated. The anticline in the base of the U of the Mazapil Region, Concepcion del Oro range, is a recumbent anticline, over to the ENE, with a necessarily subjacent recumbent syncline.

Jan 1, 1953