Search Documents

By T. B. Brooks

THE iron ores of the Marquette region are mostly extracted in open excavations; hence the process is more properly quarrying. Several attempts at underground work have been made, which have not, on the whole, been successful. The Edwards mine has been almost entirely wrought by candle-light. The slate ore pit, NO. 1, of the New England mine, is now worked in the same way, as is also the Pioneer furnace pit of the Jackson mine. The Champion mine was opened systematically for underground work, with two levels, 60 feet apart, and three shafts at distances apart along the bed of 200 feet; but this idea has been practically abandoned, the greater part of the ore in that mine being now taken out in open pits. Several other mines have occasionally worked underground stopes, but only temporarily; if such stopes could not be opened out to daylight, they have usually been abandoned. In brief, it may be said that no considerable amount of ore has as yet (1870) .been extracted underground in the region, and of that so mined very little has been taken out at a profit; and I may add that it seems to be the belief of the most experienced mining men that this state of things will hold for some time to come for reasons which will appear. Nearly the same remarks may be applied to the mines of the Iron Mountain region, Missouri, the ores of which are very similar in character to those of Marquette. Some of the New York and New Jersey magnetic deposits are wrought open, but this is the exception, underground mining there being the rule. The following brief sketch of the geological structure of the Marquette deposits will indicate some advantages of the method of mining employed. The iron-bearing (Huronian) series of rocks, are stratified beds, the principal ore formation being overlaid by a quartzite, and underlaid by a diorite, or greenstone. This ore formation is made up, first, of pure ore; second, of "mixed ore" (i. e., banded

By A. L. Holley

It has been customary at our opening sessions, for the presiding officer to address you on the general development of one or another of our several professions, or upon some important feature of Mining or Metallurgical Engineering. It is somewhat embarrassing to his successor that our former President, Dr. Raymond, expert as he is in every one of these professions, has been accustomed to keep them all, in their turn, prominently before yon. In selecting for this occasion a subject necessarily connected with iron and steel, I have thought that a review of these manufactures, with reference to some of their more pressing needs for improvement, will be more timely than a general or statistical paper. I shall endeavor to confine my remarks to a few specific defects of practice and management, and to their equally specific and more or less developed remedies. That serious defects exist; that they must be remedied ; that the manufacture is indeed already on the verge of transition, will be generally admitted. But it cannot be revolutionized all at once, however desirable the technical results might he, for that would bankrupt the business at large. We cannot afford to pull down and rebuild all our blast-furnaces that do not make a ton of pig iron with 25 cwt. of fuel; nor to replace all our hand-puddling furnaces with revolving ones, even if we could select the best revolver. Although the soft steels promise to supplant iron for most structural purposes, there are neither money nor present market to warrant all at once replacing our iron works, or half of them, with steel works. Since, then, these manufactures can neither stand still nor be suddenly metamorphosed, their managers are saying to one another: " We must feel our way into larger development; we must work gradually into better practice; we must improve a little at a time."

By John Mark Patek

Knowledge of the relative floatability of silicate minerals is increasing in importance as flotation is being applied to the concentration of nonsulfides. Many silicates are in themselves commercial products amenable to concentration by flotation. Moreover, the selective flotation of other nonsulfide minerals, such as cassiterite, depends largely upon the floatability of associated gangue silicates. Differences in floatability existing between the various silicates have not- been sufficiently appreciated; for example, the feldspars that differ greatly in floatability have generally been merely treated as "feldspar." It was the purpose of the work described in this paper to determine by experiment the differences in floatability between silicates; to investigate the causes for such differences, and to discover a means of predetermining approximate floatability without the necessity of experimentation. Determining Floatability The relative floatability of 20 silicates so selected as to represent all of the more common silicate types1 was obtained by flotation tests enumerated in Table 1. The mineral to be floated was crushed dry on a steel plate, and screened repeatedly during crushing through an 80-mesh screen in order to produce a sand with all grains as close to 80 mesh as possible. The sand was placed in dilute (6N) hydrochloric acid until free of soluble foreign material, and then washed with tap water about ten times in order to remove both acid and fines. The resultant product, which averaged 82 per cent plus 200 mesh, was floated in 50-gram charges in a 50-gram Denver celluloid flotation machine with 0.008 gram of terpineol, and from 0.01 to 0.05 gram of oleic acid in a solution acidified with sulfuric acid. The degree of separation of one mineral from another was determined by counting under a nlicroscope the grains of each mineral, both in the concentrate and in the tailings, and comparing their relative abundance in each. Unless the comparison showed a decided difference in amount,

Jan 1, 1935

Trans. Pamphlet Volume Number Title Author Meeting and Page* 1033 Relation of Air Presaure to Drilling H. W. Seamon New York 66, 743. 766 Speeds of Hammer Drills . Feb. 1921 1034 Time Factor in Depletion of Mines J. W. Roberts New York 66, 711 Feb., 1921 1035 Calculation of Ore Tonnage and Grade J. E. Harding New York 66, 117, 122 from Drill-hole Samples Feb., 1921 1038 Diacuasion of Papers Presented in 1920 1041 Run-off and Mine Drainage H. N. Eavenson New York 66. 624. 630 Feb.. 1921 1043 The Health of the Underground Worker A. J. Lanza New York Feb, 1921 1045 Dust-ventilation Studies in Metal D. Harrington New York 66, 272, 288 Mines Feb., 1921 1046 Discussion of Papers Presented at New York Meeting, 1921 1072 Breakage and Heat Treatment of Rock- B. F. Tillson New York 66. 758 drill Steel Feb., 1921 1073 Discussion of Papers Presented at New York Meeting, 1921 1076-M Analysis of Some Drill-ateel Teats F. B. Foley New York 66,789 Feb.. 1921 1077-M Application of Magnetic Analysis to C. W. Burrows New York 66, -796 Rock Drills Feb., 1921 1078-M Heat Treatment of Rock-drill Steel G. H. Gilman New York 66.779 Feb., 1921 1080 What is the Ideal Drill Steel? F. H. kingdon New York 66, 807 Feb.. 1921 1081 Rock Drill-Steels, etc. W. T. Ober New York 66,814 Feb.. 1921 1082-C Underground Mine Development, Its J. B. Dilworth Wilkes-Barre 66,715, 761 Definition and Valuation Sent.. 1921 1081 Drill Steel from Hollow Ingots P. A. E. Armstrong New York 66,809 Feb., 1921 1068 Authors' Replies to Recent Discussion 1092 Heat Treatment of Rock Drill Steel A.E.Perkins New York 66,811 Feb., 1921 1096-M Octagonal Ventilation Shaft of Davis- J. L. Bruce Wilkes-Barre 66. 252, 608 Daly Copper Co. Sept., 1921 1100-C Determination of Electrical Equip- G. Bright Wilkes-Barre 66,580,606 ment for a Mine Hoist Sept., 1921

Jan 1, 1927

By E. E. Carpenter

Believing that the results accomplished in the mill of the Churchill Milling Co., Wonder, Nev., during the fiscal year ended Sept. 30, 1914, will be of interest, I am presenting the more prominent facts and figures showing the progress made in treating this ore with especial reference to tonnage, supplies, costs, and extractions. The mill is situated at Wonder, Nev., in the Wonder mining district, 55 miles east from Fallon, Nev., the nearest railroad point. All supplies are hauled this distance by freight teams, this method of transportation having been found more reliable for continuous service than truclis, the price paid for hauling being slightly under one cent per pound. In this mill are treated the ores of the Nevada Wonder Mining Co. Ore is Unusually Hard The company which tested this ore before the mill was built reported "This ore is an unusually hard, tough, oxidized quartz, carrying a small percentage of high-grade sulphides, containing good values in both gold and silver. None of the rebellious silver minerals appear to occur in appreciable quantities." ... "In regard to the mill tonnage this ore is unusually hard and tough, and a high stamp duty cannot be expected. Using a 20-mesh screen and 1,050-lb. stamps, our best work was three tons per stamp per 24 hours." It is very probable that the ore delivered to the testing plant was harder than the regular mill run has proved to be. However, at present the mine is developed to a depth of 1,000 ft., and still shows hard ore in places at this depth in about the same proportion as on the upper levels from which the test ore came; during this year's work, ore was treated from nearly all levels. Together with this hard ore in the mill feed a considerable proportion appears to be broken down and tending to crumble, thus making an ideal mixture for stamp milling. A small proportion of talc is also noticeable, which sometimes increases in amount to the point where it is very troublesome in the thickeners.

Jan 1, 1916

By Thomas T. Read

EVERYONE engaged in the teaching of mining engineering will, I suppose, agree that the most difficult subject to teach is "Mining Methods." One primary difficulty is that the students taking the course have either had no previous experience in mining, or else they have had; either seeming to be somewhat of a drawback. The students who are unfamiliar with mines find it difficult to visualize underground conditions, as described and illustrated with sketches and maps, while those who have had underground experience seem to 'find it difficult to visualize anything much different from that which they have already seen. This reminds one of the remark about the Presbyterian doctrine of predestination, to the effect that "you are damned ,if you do; and damned if you don't."

Jan 1, 1930

By J. B. Stubbins, D. F. Coates, K. L. McRorie

Twenty-two pit slides that occurred in two Canadian open pit mining properties are analyzed. Information on the results of laboratory tests of the rocks and a brief description of the geological environment are also presented. One deduction from the study is that slides seem to be predictable by using established theory. This corroboration indicates that, contrary to normal mining practice, the appropriate slope angle should vary with the height of the wall. In addition, if the general ground water level around an open pit can be reduced, the appropriate slope angles of the walls could then be increased by a determinable amount. The ultimate objective of these investigations is to determine the relationship between the percentage probability of failure of any slope designed with specific strength paraheters. With this relationship it would then be possible to determine optimum slope angles. Because of changes in various economic factors, open pits are now being mined to much greater depths than previously. The need to keep stripping ratios low without endanrrerine.-- lives and equipment provides a strong incentive to determine the maximum practicable wall slopes. Applied research work is currently being conducted to establish the methods for analyzing optimum slopes.

Jan 1, 1963

By R. G. Robins, O. J. Kwok

The application of chemical thermodynamic theory to high temperature aqueous systems is discussed as a basis for the explanation of thermal precipitation. The derivation of high temperature potential/ pH diagrams is briefly outlined in order to show a temperature/pH relationship for hydrolytic precipitation, which is an effect that is caused simply by heating an aqueous solution. Various examples of thermal precipitation are given, with particular reference to separation of metal values from leach solutions. Metal sulphate solutions are shown to precipitate basic sulphates, hydrated sulphates , oxides, hydroxides, and oxydroxides of the metal depending largely on the pH, the concentration of metal ion, and the concentration of sulphate or bisulphate. The CuS04-H2S04-H20 system is treated in some detail, and the separation of copper from other metal ions is investigated. Other separations involving Fe, Ni, Zn, Cd, and Cr are considered. Other advantages of thermal precipitation, such as the formation of high purity, large particle size and easily filterable materials, are presented. The kinetics of thermal precipitation are also briefly examined.

Jan 1, 1973

By M. J. McPherson

Having worked on the thermodynamics of air/liquid-water mixtures passing through the surface fans of deep mines, I find this paper of great interest and congratulate the authors on producing it. There are two matters, however, deserving discussion. First, the authors have described the classical theory of fog formation with fogging occurring at "supersaturation." In fact, the process of fog formation begins well below 100% humidity. The more strongly hygroscopic nuclei in the atmosphere will attract water molecules and begin to grow at a relative humidity perhaps as low as 70%. The process is a dynamic one with both condensation and evaporation taking place throughout the mixture on microscopic liquid surfaces. As saturation is approached, the rate of condensation accelerates rapidly producing the familiar reduction in visibility. Hygroscopic nuclei are present in all natural atmospheres and under the appropriate conditions of pressure and temperature, will produce clean fogs. However, if the air is polluted by particulates from combustion or other processes then the resultant coagulation with growing liquid particles may produce dense (and sometimes photochemical) smogs. It is this process that is likely to occur in underground mines when moist air is cooled below dew point. Second, the authors have summarized very well the individual measures that might alleviate the problem. In particular, I agree that neither heating nor refrigerating the air, by themselves, provides a satisfactory solution. However, there is a combination of these that provides a neat and effective control of fog formation. This involves a small, self-contained refrigeration unit within a duct but without the usual external heat rejection facility. The air is cooled below dew point and, hence, dehumidified on passing over the cold evaporator coils. The heat from the condenser is rejected back into the air down-stream from the water eliminator, as shown in [Fig. 1]. The duct configuration can be designed to create good mixing at the outlet.

Jan 1, 1984

D. J. DEMOREST,* Washington, D. C. (written discussion ?).-This paper is a real contribution to technical science; it will make it' easier to think accurately about the inner workings of a blast furnace. I was rather surprised to read that the authors regarded as a new discovery the idea that a molten mixture of CaO, A1203, and Si02 is a molten solution of the compounds of these oxides rather than of the oxides in each other. Surely no. chemist with an active respect for the known facts of chemical affinity could believe that these oxides could be melted together without forming compounds, and that these compounds would then dissolve in one another. This work does, however, help to establish what it was supposed must be true. I think it is worth while, in the light of the work of the Geophysics Laboratory, this work of the Bureau of Mines, and that of previous investigators, to visualize what happens as a charge passes down through a blast furnace, thinking especially of the slag-forming materials. These are chiefly kaolin (Al203.2SiO2.2H2O), quartz, and limestone. These substances do not undergo much change until the limestone decomposes at about the middle of the furnace, whereupon the chemical affinities of CaO and SiO2 must begin to he active; especially if there is any amorphous Si02 present. This forms CaSiO3, and the SiO2, CaSi02 and Al2-032SiO2 then come together to form the binary and ternary eutectics so well located by the work of the Geophysics Laboratory. No matter how much lime has been charged into the furnace, the formation of this eutectic will start it about the same height in the furnace and the gangue will start to get pasty at the same height. If the charge is such that the

Jan 4, 1918

By Foster Bain

THOUGHTFUL people have raised questions as to how long nature's bank could continue to accept our drafts. These questions came to the fore so persistently, and there were so many evidences -such as the failure of natural gas in Indiana, the increasing scarcity of lumber in the Lake Superior region, the progressive sterility of Southern farm lands, the choking of the Sacramento River by tailing-point-ing to possible danger from overdraft or to misuse of resources and opportunity, that President Roosevelt called a conference which assembled at the White House on May 13, 1908, to consider these and related questions. This, the first great Conservation Congress, had a wide and beneficial influence on the thought of the world. It profoundly influenced the course of succeed-ing events and, while even yet there are sharp dis-agreements as, to the wisdom of much that has been done in the name of conservation, I believe that thoughtful men, and engineers especially, agree that the time had come when sharp attention was properly called to the waste that accompanied development of our resources. RESOURCES LARGE BUT NOT INEXHAUSTIBLE In 1908 there was a surprisingly large number of men, who should have known better, prepared to argue that our resources are "inexhaustible." No competent mining engineer, of course, believes that, as regards minerals at least. They may be, and, in most cases, fortunately are, large; as to many of them our knowledge is too general to permit measuring the reserves; but we know now, and I think the public appreciates, that there is a limit to our supply of gas, oil, coal, iron, and metals. Indeed, with the inten-sive study made necessary to meet the demands of the war, and the more careful accounting required by the newer systems of taxation, depletion has become a common word, and that mines are wasting assets has become a platitude.

Jan 8, 1922

By R. E. Hook, R. L. McGaughey, A. M. Adair

The initial yielding characteristics of a vacuum-melted iron have been measured as a function of thertnal history after slow cooling or quenching from a 700°C recrystallizntion anneal. A thermal history favoring the segregation of interstitials to grairz boundaries results in a material having high values of upper and lower yield stress and long, irregutar Luders' plateaus, wheueas specimens treated to minimize grain boundary segregation have significantly lower values of these yielding characteristics. The struc- ture of typical grain boundary areas as revealed by electron transmission microscopy is consistent with these findings. The grain boundaries in iron are considered to be principally responsible for the release of dislocations during macroscopic yielding and it is suggested that strong locking results when a substantial amount of grain boundary segregution is present; it follows that weak locking results from a more random distribution of interstitials to grown in dislocations. RECENT years have seen an increased emphasis placed on a more quantitative study of the influence of grain boundaries on the yield behavior of bcc metals. The earlier picturk of dislocation pileups at grain boundaries building up a sufficient stress concentration to unlock dislocations in neighboring grains1

Jan 1, 1967

By G. St. J. Perrott

A study of certain fundamental characteristics of liquid-oxygen explosives has been made. A discussion is given of the factors affecting the life of the cartridge and the relation between explosive strength and oxygen content. The explosive properties of L.O.X. cartridges packed with a variety of lampblacks, gas blacks, and other materials have been experimentally determined by means of the ballistic pendulum, Bichel gage, and measurement of the rate of detonation. DURING the past year, the Bureau of Mines has carried on an investigation of liquid-oxygen explosives (L.O.X.) to supplement the work described in previous publications.' The present paper gives results of the first part of this work, which was a laboratory investigation of the properties of typical combustibles used in L.O.X., and the relation of these properties to the absorption and retention of oxygen by the explosives and their explosive characteristics. No attempt will be made to describe the development of liquid-oxygen explosives, because this phase of the subject has been well covered. The L.O.X. cartridge consists of a paper wrapper filled with an absorbent combustible material that is saturated with liquid oxygen by soaking it therein. After saturation, the cartridge is removed from the liquid and fired with fuse and cap, or electric detonator, in a manner

Jan 12, 1924

By G. B. Gould

EVERY mathematical statement of a measure of anything (as distin-guished from a count) is followed by a qualification always implied if not explicity stated--that the statement is only an estimate, which may vary from absolute accuracy within certain limits, according to the accu-racy of the measuring instrument. This basic fact, so obvious to engineers, is not so well understood by many that make use of laboratory coal tests. The tolerances that must be allowed in measurements of coal quality are very important in both their commercial and engineering applica-tions-and the significance of these tolerances depends upon the use made of the laboratory coal test. Only in recent years has there been any intensive study of this ques-tion of tolerances as applied to measurements of coal quality. There is very little in our published literature on the subject, and what has been published is not, readily comprehended by those who sell coal, or buy coal and use it, unless they happen to have made a study of the subject them-selves. There is great need for more widespread understanding of what has been discovered and how it applies to the use of laboratory coal tests. What follows is an attempt to condense into a few pages the results of the major investigations so far reported, and to explain their meaning in simple nontechnical language, with the addition of some recent illustrative experiments.

Jan 1, 1937

By E. L. Tucker

PREVIOUS investigations of E. L. Tucker and R. E. Head' related in particular to the effect of cyanogen compounds on galena, sphalerite, and pyrite, and their behavior in the presence of such com- pounds. The present contribution deals with the float- ability of the copper minerals and of pyrite. All experiments were performed on minus 200-mesh material, the method of preparation being the same as that described in the previous article. Flotation tests were made in a small mechanically agitated machine of 50-g. capacity designed in this laboratory by Gates and Jacobsen." General Naval Stores pine oil No. 5 and potassium xanthate were used in constant amount in all of the experiments; these agents were selected because of their present wide use in the flotation of copper minerals. Lime additions were varied to secure four 'final hydrogen ion concentrations, namely, neutral, 0.0005 per cent CaO, 0.003 per cent CaO, and 0.02 per cent CaO. The variation in lime addition was introduced to include the range of alkalinities employed in actual flotation practice.

Jan 1, 1926

By Joseph B. Umpleby

The oil industry is at the parting of the ways in relating fundamental engineering concepts to legal interpretations and field practices. The old concept, based on an erroneous analogy to wild game, that oil and gas are migratory substances and belong to him who reduces them to possession regardless of their point of origin in the reservoir, has come to be quite generally recognized as the basis of many of the serious ills and extravagances of the industry. The chain of consequences resulting from this erroneous conception has been traced elsewhere and need not be recounted here. The important problem at this stage in the development of the industry, when laws are being revised by legislative action and modified by court decisions; when added powers are being exercised by voluntary committees and official regulatory bodies; and when the need for control of output has forced itself to the forefront, is to see to it that new law and action are based on sound engineering concepts. Reservoir Energy Common Property Since the study of gas instituted by the Marland committee of the American Petroleum Institute in 1927, a great mass of information has accumulated concerning the function of gas in the development and production of oil. This wealth of data leads to the conclusion that every oil pool contains three resources: Oil, gas and reservoir energy. I take it that the central problem of this symposium is the ownership of these three resources and that "source" and "utilization" are involved because of their bearing on ownership through the demands of equity and conservation. In order to facilitate the discussion, permit me to state categorically, that: The oil and gas in a particular tract should belong to the owners of the mineral rights in that particular tract, but the reservoir energy should be common property of all owners of mineral rights in the pool I take it that apportionment of oil and gas among owners according to the relative amounts that exist in place in their respective tracts is

Jan 1, 1933

By Henry M. Howe

This paper is a discussion of the extremely valuable one of Mathewson and Phillips, The Recrystallization of Cold-Worked Alpha Brass on Annealing,1 which not only gives us a wealth of important data reached with great intelligence, but also shows both uncommon powers of imagination and a perfectly fair spirit. Let me try to analyze some of their results, and to enunciate some of the laws to which these results point. For brevity I refer to them as "The Authors." The page numbers in parentheses refer to their paper. 1. The Visible Aspects of Recrystallization.—Plastic deformation in a single direction, as in cold-rolling, draws the grains out in that direction, that is, inequiaxes them, without destroying their apparent individuality. Each grain seems to endure the drawing out without changing either its volume or its orientation materially, for the etching tint of each grain seems to be as uniform after as before the drawing out, save for the "etch bands,"2 shown in Figs. A to D of the Authors' Plate I. As the drawn-out metal is heated progressively, on reaching a certain "disintegration temperature" these old grains seem to break up, probably into submicroscopic fragments, and this apparent disintegration is followed by a coalescence of these fragments, so that their number decreases and their size increases, till they may become very much coarser than before the drawing out. Ruder3 coarsened the grains of silicon steel in this way till single grains reached an area of 50 cm. (7.75 sq. in.). The deformation itself probably breaks each grain up into many very small fragments, but the fact that each grain continues to have a uniform etching tint different from that of its neighbors indicates that these fragments retain the initial common orientation of the grain. The apparent disintegration which we observe, then, is rather an abandonment of community of orientation for individuality of orientation, by the fragments formed earlier during the deformation. Hence we

Jan 1, 1917

By J. B. Umpleby

PRoduction engineering in 1927 may be characterized by a great. clarification of fundamental conceptions, and many improvements in technique. During the year the profession has received tnarked recogni-tion by the industry and to an extent never before attained has become an integral part of it. History Petroleum production engineering is a new profession. Prior to 1925, when this Institute undertook the work, no forum existed for the open discussion of its technical problems. There was no attempt at a handbook of the subject prior to "Petroleum Production Methods by J. R. Suman, in 1921, and no textbook prior to Petroleum Production Engineering" by L. C. Uren, in 1924. As late as 1926, only six schools and universities offered special courses in petroleum production engineering. Prior to about 1923, engineers engaged by oil companies were used almost exclusively for construction and location work. Two of the leading production engineers in the Mid-Continent field, although with their respective companies more than twelve years, were not definitely assigned to production work until 1924. Both men now head large departments giving almost their entire time to production problems. Because of the newness of the profession, the leading production engineers of today have had their fundamental training in mining, civil, mechanical and electrical courses. Not unlikely this diversified training is in considerable part responsible for the amazing growth of the profession. I believe, however, that recognition is due principally to economic pressure within the industry which has directed attention more and more sharply on costs and efficiency. After all, the justification for the growth and continued development, of the profession is to recover more oil from a given unit of sand at less cost per barrel. In this new profession, it seems to me that greatest progress will result from focusing thought and effort on this single objective, and if I might offer one suggestion to the com-

Jan 1, 1928

By Edward Norton

THE -salt deposits of the Mississippi Embayment region present a problem of origin so genetically related to the larger problem of the stratigraphy and structure of the region that a discussion of the one necessarily involves or assumes an understanding of the other. For this reason, I shall summarize briefly our knowledge of this region, emphasizing the facts related to the subject of this paper. In so doing I shall make liberal use of the reports of the National and State surveys. Geographically that section of the United States known as the Mississippi Embayment region represents a great V-shaped area, extending from near Cairo, Ill., to the Gulf of Mexico, and including Louisiana, eastern Texas, all that part of Arkansas bordering the Ouachita and Ozark mountains, western Tennessee, Mississippi, and a part of Alabama. This great section Professor Harris has described as structurally a pitching trough, its medial line being well represented by the Mississippi River. Outcropping along the border of this area are the Cretaceous and Tertiary formations, unconformably laid down on the hard Paleozoic rock sheets that show more or less plication, deformation, and faulting, depending upon their proximity to the nearby major uplifts. East and west of the Mississippi River the Cretaceous and Tertiary beds dip river- and coastward at angles greater than the slope of the land. "Waters entering along the outcropping edges of the Tertiaries and Cretaceous and following bedding planes southward are soon thousands of feet beneath the surface." As the sedimentation of the region progressed, faulting and slips occurred along planes of pre-Cretaceous weakness. Whether these movements were genetically related to the loading of this V-shaped area, as Professor Harris seems to think, is a question still to be settled. The accompanying map, Fig. 1, was taken from Bulletin No. 7 of the Louisiana Geological Survey. It shows the regional distribution of the salines, as well as an alignment of the domes, which has been assumed to indicate faulting.

Jan 1, 1915

By C. E. Van Orstrand

AN intrusive body is a mass of igneous rock that has migrated upward, presumably from great depths. Great variations in form, composition and depth of burial occur. It is not proposed in this paper to go into all of the details of the problem. Instead, it will be assumed here that the intrusive has the form and characteristics represented in Fig. I. According to W. H. Emmons,1 minerals are not deposited in appreciable quantities below the "dead line." Important amounts of ores of virtually all metals may be found around summit cupolas, but only gold, copper and zinc (in limited quantities) are usually associated with trough cupolas. Most students of ore deposits agree that temperature changes are largely instrumental in precipitating many ores in the "hood" and that the difference in temperature between the intrusive and that of the country rock may be the chief factor in determining the mineralogy of a deposit. A problem then of some interest is to correlate the principal physical features of the intrusive with the phenomena of heat conduction as evidenced by the cooling curves and the isothermal surfaces. MATHEMATICAL THEORY In order to show the possible application of heat conduction to the interpretation of the processes of metalliferous deposition associated with intrusives, it will be assumed that the intrusive is a large parallelopiped of dimensions, 2l, 2m, 2n. The equation that represents the flow of heat from the parallelopiped into country rock (v = o, t = o), which has the same thermal properties as the intrusive, is2,3 [ ] In this equation, the origin, x = o, y = o, z = o, is at the center of the parallelopiped. 'v = temperature at point x, y, z, time t. vo = initial temperature throughout the intrusive, t = o. K = coefficient of thermal diffusivity. a, ß, ? are variables of integration. Put n = m in Eq. I, and we have [ ]

Jan 1, 1944