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CONTENTS PAGE East Texas, except the Gulf Coast-H. Vance 3 Gulf Coast-L. P. Teas 8 Texas Panhandle-C. C. Rae 16 North Central Texas-H. F. Smiley 23 North Louisiana, South Arkansas and Mississippi-B. C. Craft 25 Oklahoma-C. H. Pishny, Raymond M. Carr and E. J. Dickinson 31 Kansas-E. A. Koester 35 Rocky Mountain District-C. D. Johnson 46 Illinois and Indiana-T. Wasson 49 Michigan-T. Wasson 52 Eastern States-P. D. Torrey and W. H. Young, Jr 58 West Texas and New Mexico-W. V. Vietti. Published as a Supplement.

Jan 1, 1933

By AIME AIME

Gentlemen, we have ten questions on our list and a number of us here probably have other questions to ask. Therefore, we arc going to allocate the time to these different questions so that we will try to be finished by 4:30; from then until 5 o'clock, if any of you have any questions on subjects not related, you will be free to ask them. Mr. Morton and I have changed the order of the questions. Instead of what is now first, we have put No. 3 first, progress on basic-roof construction, inasmuch as we feel that it is quite important. At this time, H. S. Robertson, of Harbison-Walker, is going to give you a short talk, with slides, on what has been done to date on this subject.

Jan 1, 1940

By John Birkinbine

Secretary's Note.—In printing this paper in the present volume, the figures given in the pamphlet edition have been brought more nearly up to date, the product of 1899 being in many instances inserted. Iron-Ore Resources. In a paper presented to the Institute in 1897,* I discussed the iron-resources of the United States as then developed, calling attention to some principal sources upon which other countries depended. The following statement will give a general idea of the amounts, as compiled from the latest official records, of ores won, and metal produced, in the nations which are important contributors to the world's output. Unfortunately these are not all contemporaneous, since in some countries the statistics do not appear until after one or more years. The statement covers not only pig-iron and iron-ore, but also manganese-ore —the manganese mined being principally used in the production of spiegeleisen or ferro-manganese, and these alloys being generally included in the pig-iron output. Table I, which epitomizes the present situation, shows respectively the countries and the quantities of iron-ore and man-

Jan 1, 1901

||Abad, Leopoldo F., Min Engr, Div of Mines, Bureau of Science Manila, P I '23 Abadilla, Quirico A, Geol, Lago Pet Corp Box 172, Maracaibo, Venezuela '20 ||Abbey, Robert Graham, The W W Sly Mfg Co Train Ave, Cleveland, Ohio '21 Abbott, A. N., Mines Supt, Mazapil Copper Co, Ltd Concepcion del Oro, Mexico '23 Abbott, Clarence E., Mgr, Mines & Quarries, Tenn Coal, Iron & R R Co, 1242 Brown Marx Bldg, Birmingham, Ala. '04 Abbott, Louis Benjamin, Chief Engr , Consolidation Coal Co , Elkhorn Div Jenkins, Ky. '16 Abbott, Robert R., Met Engr , Peerless Motor Car Co Cleveland, Ohio '12 ||Abbott, Wells Osborn, Ray Consolidated Copper Co Hayden, Ariz. '23 Abeel, George H, Jr., Cons Min Engr 4612 West 17th St , Los Angeles, Cal '18 Abel, Albert E., Asst to Pres, Valley Mould & Iron Corp Sharpsville, Pa. '19 Abernathy, George Elmer, Prof of Geol & Min , Kansas State Teachers College, Pittsburg, Kans. '20 Abey, Hiroshi, Min & Met Engr, Min & Met Dept, The Higher Technical School, Osaka, Japan. '17 ||d'Ablaing, Philip R, Chem , Anaconda Copper Min Co Great Falls, Mont '25 Aborn, Robert H , Research Assoc., Mass Inst of Tech Cambridge, Mass '19 Abouchar, Sylvain Sley, Min. Engi & Geol , care of S H Sekaly, 13 Rue El Nimr, Cairo, Egypt '17

Jan 1, 1923

By AIME AIME

THE following paragraphs, constituting the concluding portion of the Annual Report of the Council for 1903, have been withheld from publication until now, in order to make them as accurate and complete as possible. They will be published in Volume XXXV. of the Transactions in their proper place at the end of the said Annual Report. Franklin Ballou was born in Pittsburg, Pa., May 29, 1845. He was the son of an old resident, Arthur Ballou, a manufacturer and wholesale dealer in vinegar. In early youth Franklin attended the Western University of Pittsburg, but left school at the age of 16 to become book-keeper for his father, upon whose retirement from business, in 1868, he associated himself with Walter C. Childs, of Pittsburg, in the manufac¬ture of furnace-grates and asbestos-cement for blast-furnaces. This firm was known as W. C. Childs & Co., and did a success¬ful business for several years. In 1869 Mr. Ballou married Miss May S. Wilson, daughter of Judge Wilson, of Lewistown, Pa. In 1876 he spent several months traveling in the West and studying the mining industry, which greatly interested him. In consequence of this journey, he wound up his business in Pittsburg and removed in 1877 to Georgetown, Colo., where for several years he conducted a sampling-works, and built up an extensive business as an agent for the sale of ores, besides engaging to some extent in mining enterprises. , It is said that he controlled at one time about one-eighth of the output of the Leadville mines. In the early 80's, he became Vice-President and General Manager of the Bimetallic Smelter at Leadville, of which Mr. David H. Moflat was the principal owner. This was practically the first successful demonstration of pyritic smelting in Colorado. Upon the sale of the works in 1897 to the American Smelting and Refining Co., Mr. Ballou retired

Jan 1, 1905

By J. M. Dahl, L. H. Van Vlack

STAFF: Editor, Gerhard Derge Associate Editor, Paul G. Shewman Carnegie lnstitute of Technology Schenley Park Pittsburgh, Pa. 15213 Editorial Assistant, M. A. Redmerski Production Editor, Otto T. Johnson THE METALLURGICAL SOCIETY: Jack H. Scoff, President; Richard C. Cole, Post-President; Harold B. Emerick, President-Elect; Ralph L. Hennebach, Treasurer; Robert W. Shearman, Secretary; Donald A. Parks, Assistant Secretary; Leslie S. Wilcoxson, Assistant Secretary. PUBLICATIONS COMMITTEE OF THE METALLURGICAL SOCIETY: R. E. Lund, Chairman; T. E. Dancy, H. B. Emerick, P. R. Gouwens, R. E. Grace, J. H. Jackson, H. H. Johnson, A. E. Lee, Jr., R. R. Nosh, R. D. Pehlke, and Paul Queneau. Review and selection of monuscripts is under the supervision of the following Publications Committees: Extractive Metollurgy Division: R. E. Grace, Chairman; G. M. Bell, D. W. Bridges, J. M. Cigon, G. W. Healy, T. A. Henrie, R. D. Holli-day, C. E. O'Neill, C. S. Sami s, A. W. Schlech-ten, and Charles Shull . Iron and Steel Division: R. D. Pehlke, Chairman; T. P. Floridis, Arnulf Muon, G. R. St. Pierre, E. T. Tuckdogon, L. H.Von Vlack, and J. M. Uys. Institute of Metals Division: H. H. Johnson, Jr., Chairman; J. B. Clark, Vice Chairman; M. R. Achter, G. F. Bolling, J. O. Brittain, G. P. Conard, II, L. A. Girifolco. G. T. Hahn, J.P. Hirth, L. Himmel, G. T. Horne, George Krauss, C. F. Leitton, Jr., J. D. Livingston, R. D. Monning, H. M. Otte, S. V. Radcliffe, R. E. Reed-Hill, H. C. Rogers, O. Sherby, M. T. Simnod, G. R. Speich, E. A. Steigerwold, R. A. Swolin, W. A. Tiller, W. R. Upthegrove, J. B. Wagner, Jr., Derek Walton, H. W. Weart, W. W. Webb, and D. WiIsdorf. Published monthly by the American lnstitute of Mining, Metollurgicol, and Petroleum Engineers, Inc., 345 East 47th Street, New York, N. Y. 10017. Telephone PLAZA 2-6800. Subscription $30 per year for non-AIME members in United States and North, South, and Central America; $32, foreign; $7.50 for AlME members. Single copies, $6.00, single copies foreign, $6.50. The AlME is not responsible for any statement mode or opinion expressed in its publications . . . Copyright 1965 by the American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. . . . Registered cable address, AlME New York . . . Indexed in Engineering Index, lndustrial Arts Index, and Chemical Abstracts . . Second class postage paid at New York, N. Y., and Ann Arbor, Mich. Volume 233, Number 1.

Jan 1, 1965

By S. B. Christy

Jan 1, 1902

CORPORAL SHEPPARD B. GORDY Sheppard B. Gordy, a brief biography of whom was printed inn the January Bulletin, entered the employ of the Braden Copper Co. immediately on his graduation from the Sheffield Scientific School in 1912. He remained with this company four years, working up through the various grades to assistant foreman and foreman to one of the individual mines. The last year he was in its employ, he acted as general mine foreman. He was for a short time with the Chile Exploration Co. and then went with the Andes Exploration Co. (Anaconda) and remained with CORPORAL SHEPPARD B. GORDY. the latter, doing mine exploration and development work, until he sailed for home in June, 1918, to give a more personal and active service to his country in her need. He declined a tender of induction into an officers' training camp, at the urgent request of Professor McClelland supplemented by Mr. Potter, because they demonstrated to his satisfaction that he could give more valuable service to his country in helping out with the aircraft production. Being within the draft age, in order to carry out this plan, it was necessary for him to be called by his Local Board and sent to camp. This call came Aug. 26. Two weeks before that time lie had gone to Dayton, Ohio; to begin the study of aircraft production, and was sent by the Dayton Board to Camp Sherman, Chillicothe, Ohio, where he died of pneumonia on Oct. 9.

Jan 3, 1919

By Lester A. Blackner

Discussion of the paper of LESTER A. BLACKNER, presented at the San Francisco meeting, September, 1915, and printed in Bulletin No. 102, June, 1915, pp. 1249 to 1290. SIDNEY J. JENNINGS, New York, N. Y.-In the historical part of the development of the caving system discussed by Mr. Blackner, I notice the absence of one man's name, Charles Henroten. Mr. Henroten used the caving system in South Africa in the. Kimberly mines, and realized from his work there that ground would cave when properly prepared. I think it is due him that his name should be mentioned in connection with an exposition of this system in America.

Jan 12, 1915

(Members are urged to send in for this column any notes of interest concerning themselves or their fellow-members.) The following members registered at Institute headquarters during the month of April: J. C. Ralston, Spokane, Wash. E. P. Ross, Johnson City, Tenn. C. H. James, London, Eng. F. L. Garrison, Philadelphia, Pa. E. H. Benjamin, Oakland, Cal. A. Radcliffe, Copiapo, Chile. W. H. Shockley, Palo Alto, Cal. S. S. Wyer, Columbus, Ohio. A. C. Mauney, Salisbury, N. C. W. B. Kunhardt, Reading, Pa. A. W. Newberry, Los Angeles, Cal. W. E. Saunders, Philadelphia, Pa.

Jan 5, 1913

EXECUTIVE COMMITTEES OF LOCAL SECTIONS New York LOUIS D. HUNTOON, Chairman. ARTHUR S. DWIGHT, Vice-Chairman. THOMAS T. READ, Secretary, Woolworth Bldg., New York, N. Y. E. MALTBY SHIPP, Treasurer. GEORGE F. KUNZ. W. DE L. BENEDICT. Boston ROBERT H. RICHARDS, Chairman. ALBERT SAUVEUR, Vice-Chairman. AUGUSTUS H. EUSTIS, Secretary-Treasurer, 131 State St., Boston, Mass. TIMOTHY W. SPRAGUE, HENRY A. WENTWORTH. Columbia F. A. THOMSON, Chairman. GEORGE W. RODDEWIG, Vice-Chairman. LYNDON K. ARMSTRONG, Secretary-Treasurer, P. 0. Drawer 2154, Spokane, Wash. R. S. McCAFFERY, S. H. RICHARDSON.

Jan 4, 1914

By S. A. Levy, J. D. Wood, J. F. Libsch

A study of the preparation and characteristics of a sevies of Fe-C-N alloys has been conducted. X-ray, microhardness, and metallographic data from a series of single-phase alloys produced by controlled nitriding of carburized foils are reported. The existence of a, y', and E carbonitride has been confirmed and it has been found that y' is the hardest of these three phases. These results have been used to interpret the structures observed in nitrided steels. ThIS paper represents the second phase of a three-part study concerning combined nitriding and induction hardening. The first part' reports the engineering properties (depth hardness, fatigue, corrosion, and tempering resistance) obtained when seven different steels were subjected to the combined surface hardening treatment. The present paper concerns the nature of a series of single-phase alloys prepared by controlled nitriding of carburized foils. The objective was to simulate the various layers present in the as-nitrided steels. A third paper will report data concerning induction hardening of the foils and will attempt to set forth a mechanism for the high hardness obtained with the combined treatment. Studies of nitriding generally fall into three categories. The first were performed with bars using conventional nitriding procedures, thus yielding a nitrogen gradient and a series of phase layers near the surface.2-6 Such studies were complicated by the presence of the nitrogen gradient, for it was difficult to correlate microhardness and X-ray data with chemical composition. There were always complications due to penetration of the X-ray beam which yielded data influenced by underlying layers. Similar difficulty was experienced in taking hardness readings on a tapered specimen or in isolating various layers by machining. A second group of investigations was primarily concerned with establishment of regions in the Fe-N7,9,10 or the Fe-C-N phase diagram.8 These were performed with powder specimens which were nitrided in am-monia-hydrogen mixtures to produce a series of single-phase specimens. Unfortunately, the powder specimens were not amenable to either microstruc-ture or microhardness study. The third was essentially a compromise of the first two. Bose and Hawkes," using 0.005-in.-thick iron foils, were able to obtain microhardness, microstruc-ture, composition, and X-ray data on Fe-N alloys of eutectoid composition by equilibration in ammonia-hydrogen mixtures at 1290°F. To obtain a better understanding of the nitriding process and the characteristics of the phases in ni-trided plain carbon steels, the present investigation was undertaken. The investigation was patterned after that of Bose and Hawkes with the exception that nitriding was performed at 930°F (below the eutectoid temperature), as in the case of conventional nitriding. In addition to gaining some understanding of the source of high hardness of nitrided and induction-hardened steels, found in a previous study,' this investigation was concerned with the possibility of controlling the phases present in a nitrided case through the use of ammonia-hydrogen mixtures. Knowledge of the properties of each phase and the conditions necessary for its production could make it possible to avoid undesirable surface layers in nitriding. EXPERIMENTAL PROCEDURE Specimen Preparation. A specimen thickness of 0.005 in. was selected to insure that a uniform nitrogen concentration could be obtained in a reasonable length of time by equilibration in an ammonia-hydro-gen atmosphere. The starting material was a vacuum-cast ingot of pure iron, the major impurities of which were: C, 0.003 pct; 0, 0.014 pct; S, 0.004 pct; N, 0.003 pct.* 'Compositions are quoted as weight percent except as noted. The ingot was heated to 1500°F in a nitrogen atmosphere and forged to a slab 0.25 in. thick. The material was then reduced to 0.005 in. by alternately cold rolling and annealing in a nitrogen atmosphere at 1600°F. This material was divided into five groups of specimens which, after carburizing, yielded the following carbon contents: 0.003, 0.28, 0.36, 0.46, and 0.74 pct C. The carburizing was performed by the Leeds and Northrup Research Laboratories, using a controlled "carburizing potential" which yielded a uniform carbon concentration throughout the cross section.

Jan 1, 1970

THE Nominating Committee appointed at the Division meeting in October and consisting of Frank A. Herald, A. W. Peake, C. R. McCollom, Joseph Jensen, H. W. Camp, C. P. Watson, F. Julius Fohs, George Otis Smith, J. B. Umpleby, J. M. Lovejoy and A. W. Ambrose, have presented the following ticket for the year 1929: Chairman, Joseph B. Umpleby; associate chairman, A. C. Rubel; secretary-treasurer, R. Van A. Mills; vice-chairman for Economics, Warren A.. Sinshein~er; vice-chairman for Engineering Education, H. C. George; vice-chairman for Engineering Research, Harry H. Hill; vice-chairman for Production, C. P. Watson;vice-chairman for Refinery Engineering, A. D. David. For Production Engineering Charles V. Millikan. is named vicechairman, with ,Charles E. Beecher, Glenn D. Robertson and W. W. Scott as associate vice-chairmen. The Executive Committee named is to consist of Joseph B. Umpleby, chairman with A. W. Ambrose, Charles E. Beecher, A. D. David, Glenn D. Robertson, H. C. George, Harry H. Hill, John M. Lovejoy, Charles V. Millikan, R. Van A. Mills, Earl Oliver, A. W. Peake, A. C. Rubel, W. W. Scott, Warren A. Sinsheimer and .C. P. Watson, members. Ballots will be mailed to members of the Division.

Jan 1, 1928

By JOHN W., E. C. SARCENT

The South Texas area discussed herein represents districts 2 and 4 of the Texas Railroad Commission. It extends from Jackson, Lavaca and Gonzales Counties on the northeast to the Rio Grande River, and comprises a total of 26 counties.

Jan 1, 1946

By Oliver C. Ralston

This paper reports the results of the use of salt in some research work carried on during the past 3 years at the Salt Lake City Station of the Bureau of Mines, which is quartered in the University of Utah, whose Metallurgical Research Department cooperates with the Bureau. Only the work involving the use of salt is described. The authors wish equal credit given to J. F. Cullen, C. L. Larson, C. Y. Pfoutz, C. E. Sims, H. C. Neeld, R. W. Johnson, F. G. Moses, N. C. Christensen, and G. H. Wigton, who have all in some way contributed toward the success of this work, while connected with the station in one way or another. Lead Metallurgy Popularly Supposed to be Without Problems In lead metallurgy it is difficult at first to find metallurgical problems, as the prevailing conception has been that lead is so easily concentrated in its various ores and so easily reduced to its metallic form that the only progress possible is that involved in cheapening methods of mining and of reduction. Most of the problems usually considered are of minor nature and do not involve radical metallurgical changes. During the three years of work of the Salt Lake Station, the following classification of problems in the metallurgy of lead has been made: Oxidized Ores. 1. Ores containing only lead. 2. Ores containing lead and silver or gold. 3. Ores containing lead and zinc, with or without silver. Sulphide Ores. 1. Ores of pyrite carrying some lead. 2. Ores of complex zinc-lead-iron sulphides. 3. Complex sulphides containing precious metals.

Jan 1, 1918

By AIME AIME

The XCVIIth meeting of the Institute for the reading and discussion of papers will be held at Spokane, Wash., beginning Monday, Sept. 27, 1909, as already announced in Special Circulars of May 8 and Aug. 14, 1909, and in the Bulletins for June, July, and August. The meeting will be preceded by a tour through Yellow stone Park and visits to Butte and Anaconda, and will be followed by visits to the Coeur d'Alene district, to the Alaska-Yukon-Pacific Exposition at Seattle, to the mining- and smelting-plants near Salt Lake, and to the iron- and lead- and zinc-plants at Pueblo. The special train for the party' will leave Chicago, September 16, and return about October 12. Details of the itinerary are given later in this announcement. The Secretary of the Spokane Local Committee is Lyndon K. Armstrong, 615 Hyde Block, Spokane, Wash., to whom should be addressed all inquiries concerning local matters. The control of the papers and proceedings will remain in charge of the Institute office, as usual. It is greatly to be desired, both in behalf of the Institute and in recognition of the many courtesies to be extended on the trip, that the excursion party be made larger. Exceptional facilities to visit the many mines and smelters have been freely provided; and members are requested to make all reasonable effort to attend the meeting at Spokane and participate in the excursions. For those who cannot join in the entire trip, it may be possible to provide special Pullman accommodations after leaving Yellowstone Park. In order to make the necessary arrangement, however, the names of members and guests contemplating this partial trip should be sent at once to Theodore Dwight, 29 West 39th Street, New York City. The general cost of the trip per member will be $300, which includes transportation, berth, and meals for the entire trip from

Sep 1, 1909

By C. A. Stewart

I. INTRODUCTION AND GENERAL STATEMENT OF RESULTS. The field-work upon which this paper is based was done in the summer of 1910, and was made possible by the courtesy of the Imperial Copper Co., which gave me access to its property. For their kindness in this respect I wish to express my thanks to W. F. Staunton and Meade Goodloe. Moreover,. B. F. Smith and G. B. Gentry, mining engineers in the employ of the company, gave invaluable assistance by placing maps,. etc., at my disposal, and by discussing with me the problems of the district; and it is a great pleasure to acknowledge this indebtedness to them. In order that the significance of some of the details that follow may be better appreciated at first reading, a general outline of the conclusions reached is given here. In the Silverbell mining-district a series of Palaeozoic limestone blocks is completely surrounded by post-Palaeozoic igneous rocks, intruded in the following order: alaskite, alaskite-porphyry, biotite-granite, andesite, and quartz-porphyry. The biotite-granite is believed to represent a differentiation of the. magma from which the alaskite-porphyry came ; and this conclusion-has an important hearing on the origin of the ores. The intrusion of both alaskite-porphyry and biotite-granite was followed by the emission of magmatic waters, which sericitized and silicified the alaskite-porphyry and granite, and produced in the limestone, by the addition to it of silica, iron, and alumina, great masses of garnet, quartz, and wollastonite. Following close upon these solutions came metal-bearing magmatic waters, which impregnated porphyry, granite, and alas kite with cupriferous pyrite, and deposited in the garnet zones chalcopyrite and copper-bearing pyrite that make important bodies of contact-metamorphic ores. Secondary enrichment has taken place in the disseminated ores in the igneous rocks,. raising their copper-content to 2 per cent. in some cases,. and extensive drilling has been undertaken to block out these deposits. East of the contact-metamorphic deposits there is a fissure-vein of lead-silver ore in the quartz-porphyry. This rock is distinctly younger than the alaskite-porphyry and the granite; and the lead-silver ores belong, therefore, to a period of mineralization distinctly later than the copper-deposition.

May 1, 1912

By Robert Bell

THE " Tar-Sands." is the name which has been given to the extensive horizontal deposit of fine Cretaceous sand, blackened by tarry petroleum, which forms the banks of the last or lowest 130 miles of the Athabasca river before it terminates in Athabasca lake. The Cretaceous strata, to which these sands belong, extend northwesterly from Dakota all the way to this lake and for 500 miles beyond it. The Athabasca river forms the uppermost section of the Athabasca-Mackenzie, one of the great rivers of the world. It rises on the Pacific side of the Rocky mountains, westward of Edmonton, and flows north of east to a point called Athabasca. Landing, 100 miles north of Edmonton, where it turns northward and runs about 280 miles before it falls into the west end of Athabasca lake. The section of this river-system which discharges the lake just named into Great Slave lake, is called Slave river, and below the latter lake it becomes the Mackenzie river. Along the section of 280 miles of the Athabasca river above mentioned, the Cretaceous strata consist of bluish-gray and drab-gray marls, on top, from Athabasca Landing to Drowned rapid, 110 miles down stream; then heavily bedded gray sandstones, 225 ft. in greatest thickness, underlying these, form the banks for about 40 miles further. The strata appear to be horizontal, but they really clip very slightly to the southward. At Drowned rapid, we see the first of the tar-sands resting on almost horizontal beds of bluish-gray limestone of Devonian age. In some places the limestone is associated with shaly or marly bands. Notwithstanding the great hiatus between the two series, the horizontal tar-sands lie conformably upon the almost level upper beds of the limestone wherever the two formations are seen together, all along the river, throughout a

Mar 1, 1908

By Sherwin F. Kelly

THIS is intended as a simple review of the principles and practice of geophysics, so will not be of interest to the geophysicist, who is hereby warned of its elementary character. The engineers for whom it is written are those who, having glimpsed the formidable formulas and discussions of the geophysicists, give all publications on the subject a wide berth. For a few years now the geo-physicists have had a tendency to be ingrowing at their meetings, going deeper and deeper into theory and instrument construction, and forgetting to present the topics that would interest the practicing engineer who desires merely to know how geophysics can help him, not why.

Jan 1, 1934

By B. B. Bucky

THIS investigation was carried on by means of models and the applica-tion of the principles of similitude to determine the effects of props, props and cribs and sand filling in longwall mining. The geologic structure and rate of face retreat were kept constant and the only change introduced was in the method of support. It is not felt necessary to repeat a description of apparatus, or to explain the fact that a scalar model made in all parts of the same material as the prototype will behave similarly to the prototype when rotated at speeds such that the centrifugal force is as many times the gravitational force as the prototype dimension is a similar linear model dimensions. The reader is referred to earlier papers1,2 for further information regarding these statements. All models were made of sandstone and were as in Fig. 6. They are composed of a 3/16-in. ore body bed A, overlain by a 3/16-in- bed B, a 3/8-in, bed C and two 1/8 -in. beds D and E. The model was rotated at ±2350 r.p.m. equivalent to a model ratio of 1268. It was worked back 1/4 in. at a time before being replaced in the centrifuge and again rotated. Table 1 gives model and prototype dimensions occurring in this discussion, the prototype dimensions being 1268 times the model dimensions. Figs. 1, 2, 3 and 4 were taken while the model was rotating at 2350 r.p.m. One was taken for each face retreat of 26.4 ft., but for obvious ,reasons all are not presented. Fig. 1 (A-E) shows the behavior of this type of structure with face retreats of 26.4 ft, and no artificial support. Fig. 2(A-E) shows the behavior of this type of structure where breaker and face props were used. The props were exceptionally strong, being of steel 1/8 in. square in cross section, and capped with 1/16 in. ± of soft wood and paper, to allow for roof deflection. The face props were

Jan 1, 1939