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By P. A. Toynbee

An experimental air-slide classifier1 has been applied to the de-dusting of ground dolomite in an attempt to produce a grade of -30 +150 mesh (B. S. Sieves) material from a raw material containing 30-35% of the -150 mesh fraction. Air flows varying between 1.5 and 2.5 cu ft/sec sq ft of screen area were used. The throughput of dolomite was between 80 and 100 lbs/h. inch of screen width. The size analyses of the de-dusted material and of the original dolomite are shown in table at right. The proportions of the +100 mesh material in the feed and in the de-dusted products have been used to calculate materials balances, on the assumption that there is no loss, as dust, of this +100 mesh fraction. By interpolation, it can be shown that a de-dusted product recovery of 68.5% will be obtained at an air flow of 2.13 cu ft/sec sq ft of screen area. The feed material contains 68.5% of +150 mesh material, so that if the de-dusting gave a perfectly sharp cut, the product would contain no material less than 150 mesh. Further calculations based on the size analyses, show that, at an air flow of 2.13 cu ft/sec sq ft of screen air, the -150 mesh fraction in the de-dusted product will fall just below the specified maximum limit of 5%.

Jan 1, 1964

Roof Bolts An expansion shell and plug Westinghouse roof bolting assembly made for use with threaded steel rods and large flat washers or steel channel employs a plug larger in diameter than those for trolley wire service. The notched plug helps prevent shell and plug from turning. The unit is shipped complete. Circle No. 1 Fan The Jeffrey Mfg. Co. Aerodyne Midget fan is a self contained blower or exhauster for auxiliary ventilation through tubing. Operating rating with 5 hp motor is 6.5 in. maximum static pressure, and 6200 cfm free delivery volume. Weight is 340 to 475 lb and it may be furnished in open or permissible form. Circle No. 2 Heavy-Density Initial installation in the Mesabi Range country of the Wilmot-Daniels heavy-density concentrating system was a 175 ton per hour plant at the [ ] Skubic Bros. Virginia, Minn., operation. This Wilmot Engineering Co. unit has a separatory vessel providing unidirectional medium flow and as the only moving part uses a standard drag-line conveyor for lifting sink out of the bath. Circle No. 3 Portable pH Meter A low priced battery-operated portable pH meter of utmost simplicity announced by the Photovolt Corp. uses only 3 ordinary radio batteries which give over 2000 hours of service. Accuracy of 0.03 pH is claimed by the manufacturer for the model 125, and AC power line supply is available. Circle No. 4

Jan 1, 1952

By L. L. Hirsch, W. M. Parris, P. D. Frost

IT has been established that titanium alloys con- taining sufficient amounts of ß-stabilizing elements, such as iron, chromium, or manganese, can be age hardened.' Adenstedt, Pequignot, and Raymer2 showed that age hardening occurred in a Ti-15 pct V alloy at room temperature after it was quenched from a temperature in the ß-phase region. During a recent investigation of the heat-treating characteristics of binary Ti-Mn and Ti-Cr alloys at Battelle, further evidence of low temperature aging was found. Appreciable hardening occurred in some of these alloys at aging temperatures as low as 212 OF (100oC). Indeed, the brief heating period employed for mounting metallographic specimens in bakelite resulted in hardening. It was felt that further information on this low temperature aging phenomenon would be of general interest in view of the large amount of work currently being done on titanium alloys. The alloys examined in this investigation were arc-melted in a water-cooled copper crucible as 3/4-lb ingots. Du Pont Process A sponge was used as a base material. The arc-melted ingots were forged at 1700" to 1800°F (927" to 982°C) and hot rolled at 1450°F (788°C) to 14 gage (0.064 in.) sheet. Small specimens were heated in argon at 1742°F (950°C) for 30 min and quenched in various liquid media or air cooled. They were then mounted in a room-temperature-setting resin and given a metallographic

Jan 1, 1954

By W. W. Tyler, A. C. Wilson, L. B. Nesbitt

INVESTIGATIONS of thermal conductivity and impact strength of the titanium alloy RC-130-B and 316 stainless steel were undertaken because of interest in strong, nonmagnetic, commercially available alloys of low thermal conductivity for use in low temperature experiments. Measurements of electrical resistivity and thermoelectric power were also made for some of the samples studied. The titanium alloy designated as RC-130-B is manufactured by Rem Cru Titanium Inc. It contains 0.14 pct C, 3.99 pct Al, and 4.7 pct Mn. A general discussion of properties of the two phase Ti-4Mn- 4A1 alloys is given by Finlay and Vordahl.' The alloy is machinable and has a yield strength greater than 130,000 lb per sq in. at 0.2 pct offset. The 316 stainless steel sample used for both conductivity and impact strength measurements was obtained from the Allegheny-Ludlum Steel Corp. and is designated as Allegheny metal 18-8M, Type 316, Grade 316. The sample had received 25 pct minimum final cold reduction and had a Brine11 hardness rating of 255. Several impact tests were made on a sample of 316 stainless which had not received the 25 pct cold reduction. Also several data points are reported giving thermal conductivity and electrical resistivity for a sample of 304 stainless steel taken from stock. Figs. 1 and 2 give thermal conductivity and electrical resistivity data for the titanium alloy and for

Jan 1, 1954

By G. J. Wolga, W. W. Tyler, A. C. Wilson

THE physical properties of uranium have been reviewed by Katz and Rabinowitch.1 Their review includes thermal conductivity data for ternperatures above 375°K. Recently, Mendelssohn and Rosenberg' have published data on the thermal conductivity of uranium from 2" to 20°K. Our measuremerits indicate the temperature dependence of the thermal conductivity in the temperature interval from 20" to 300°K. Electrical resistivity and thermoelectric power were measured on the same sample. The material studied was normal uranium which had been heated at 700°C in a lead bath for 10 min and then quenched in a water bath held at 50°C. From this material a rod M in. in diameter and 2 1/2 in. long was machined. Two 0.040 in. holes were drilled into the rod 1 3/4 in. apart. Copper-constantan thermocouples for temperature and potential measurements were soldered to copper pins which were pressed tightly into these holes. Details of the equipment and experimental techniques used in making the measurements have been described elsewhere." Fig. 1 shows micrographs of a section of the sample studied. Fig. la was taken with unpolarized light and shows impurity inclusions, probably uranium carbide. Fig. lb, showing the same field, was taken with polarized light and gives some indication of the grain size and twinning within the grains. Experimental Results Thermal conductivity and electrical resistivity data are shown in Fig. 2. Table I shows values of

Jan 1, 1954

By George W. Maynard

In the Journal of the Iron and Steel Institute for the year 1878, in the account of the proceedings of the annual meeting in March of that year, when Mr. Bell read his paper On the Separation of Phosphorus from Pig-Iron, occurs the following statement, as part of the reported discussion of that paper: " Mr. Sidney Thomas stated that he had succeeded in effecting the almost complete removal of phosphorus in the Bessemer process. Experiments had been carried on at Blaenavon, with the co-operation of Mr. Martin, on quantities varying between 6 lbs. and 10 cwt., and some hundred analyses made by Mr. Gilchrist (who had the conduct of the experiments from the first) showing the removal of from 20 per cent. to 99.9 per cent. of phosphorus in the converter. He believed the practical difficulties in the way had been overcome, and that Cleveland pig might be made into good steel without any intermediate process. He hoped on a future occasion to lay full details before the Institute." I was present at that meeting, and I doubt if any one in the hall knew, either by sight or name, the young man who had dared to rise in that august body and claim that he had accomplished that after which the great metallurgists of Europe had been unsuccessfully striving ever since Mr. Bessemer's great discovery. I remember distinctly the pitying smile of derision and the stony stare

Jan 1, 1885

By D. C. Buffum, L. D. Jaffee

THAT the path of brittle fracture in temper brit-tle steel differs from the path in unembrittled steel has been known for some years1 More recently it has been recognized that alloy steels, at least, display two forms of temper brittleness1 which may be called upper-nose and lower-nose. No experimental evidence has been published, however, to show that the two forms can be distinguished by simple inspection of brittle fractures. Fig. 1 is a photograph of the fractured surface of a V-notch Charpy specimen of SAE 3140 steel in which temper brittleness developed during heat treatment in the lower-nose temperature range.' The steel was austenitized 1 hr at 900°, tempered 1 hr at 675", and embrittled 48 hr at 500°C, with water-quenching after each treatment. The temperature of transition from ductile to brittle fracture in the Charpy test was + 2°C (criterion of transition: 100 pet fibrous). The hardness was Re 25; the austenite grain size ASTM 8. This specimen was broken at 150°C in the standard Charpy test and absorbed 6.6 ft-lb; its fracture was rated 0 pet fibrous. Fig. 1 shows that the fracture appeared rough to the naked eye. At the side of the specimen away from the notch (the side which was in compression during the test), the surface as a whole deviated sharply from a plane. At higher magnification, X60, the surface gave

Jan 1, 1959

ON FEBRUARY 13, 1953 the Miami Copper Company signed a contract with the United States Government, through the Defense Materials Procurement Agency, whereby it under- took, with a base price of 27.359 per lb (subject to escalation based on wage scales and wholesale-price indices), to exploit a new ore body in its mine in Gila County, Arizona. Recoverable ore was estimated at 23,000,000 tons, averaging about 0.677 per cent copper. Moreover, the proportion of oxidized copper, difficult to recover by flotation concentrating, was so high that an average net recovery of only ten pounds per ton (0.5 per cent) was expected. The company proposed to mine the ore by the underground method known as undercut block-caving. Unfortunately the ore body, as has been true of all Miami's ore bodies, lay so deeply buried that no possibility existed of adopting opencut mining as has been done in recent years at Miami's neighbors, Ray and Inspiration. Probably the most distinctive characteristic of Miami's operations has been the extent to which it has developed and improved methods and equipment for underground mining. True, necessity was a potent stimulant, because its available ores since 1926 have been exceptionally low-grade; so, if the enterprise were to survive, it was necessary to keep costs at the minimum. This fact does not detract, however, in any way from the remarkable achievements of Miami engineers in conducting efficient and low-cost underground mining.

Jan 1, 1957

GENERAL Broken Hill lies at latitude 31º58'S longitude 141º27'E on the semi-arid western plains of New South Wales. From discovery in 1883 until the end of 1969 the lead-silver-zinc orebody has yielded 107,570,000 tons of ore for an overall grade of 13.1% Pb, 6.9 oz Ag/ton and 9.4% Zn.* The orebody currently supports the activities of four mines which are, from north to south, North Broken Hill Limited, Broken Hill South Limited, The Zinc Corporation, Limited and New Broken Hill Consolidated Limited. It is estimated that in 1969 these mines produced about 8 ½ % of world lead production and about 6% of world zinc production. In 1905 The Zinc Corporation, Limited was founded to recover zinc from tailings dumps and moved into mining in 1911 on leases purchased from Broken Hill South Limited at the then southern extremity of the "line of lode". New Broken Hill Consolidated Limited was formed in 1936 to explore and mine for deep ore in the leases to the south of The Zinc Corporation which were purchased from Barrier South Limited. The Zinc Corporation, Limited and New Broken Hill Consolidated Limited mines are both managed by Conzinc Riotinto of Australia Limited, which wholly owns The Zinc Corporation, Limited and has a 32% interest in New Broken Hill Consolidated Limited. * Throughout this paper tons referred to are long tons of 2,240 lbs.

Jan 1, 1970

By H. W. Montz

THE problem of surface support in coal mining is naturally divided into three branches: 1. Surface covered with improvements of such value as compared with the value of the underlying coal, or with such elements of danger to mining, that absolute support is essential. 2. Surface with improvements of less value than the underlying coal such that moderate settlement may be permitted, but destructive settlement must be avoided, either by reason of danger to human life or unwarranted property damage. 3. Surface of relatively small value as compared with the underlying coal where destructive settlement may be permitted. First Problem In the first case it is evident that the original support must be maintained either (a) by leaving ample pillars and confining the coal recovery to a very conservative first mining, (b) by so supporting less conservative first mining by filling or flushing that the gradual deterioration of the pillars may be prevented and subsidence avoided, or (c) by incompressible support as masonry either as an adjunct to insufficient pillars or in place of the original coal support. a. From tests made by the Scranton Engineers Club, it appears safe to figure on 2000 lb. per sq. in. as the safe squeezing strength of coal pillars in place, provided that these are, as usual, not higher than their least horizontal dimension; and from this figure the percentage of pillar to be left for various depths may be easily calculated. For safety in this

Jan 1, 1928

By William F. Boericke

THE Christy Creek clay mine of the General Refractories Co., in the Olive Hill District, ranks with the most important producers in the north-eastern Kentucky fire clay field, both from production of high-grade flint clay, as well as unusual extent and thickness of deposit. The property is but one of a number controlled by the General Refractories Co. in this district, but is given first consideration among them by the operating staff. Its total area is over 5000 acres, owned in fee or by lease of clay mining rights, and although mining operations have been in progress for over five years, scarcely one per cent of the ground has been worked as yet. The mine is near the southwestern end of the clay field, which extends in a belt 12 miles wide and 55 miles long, in a southwestern direction from Kenova, W. Va., which, as the name indicates, is at the junction of Kentucky, Ohio, and West Virginia. Olive Hill, where there is one of the l1Ulin plants of the General Refractories Co., and to which the clay from the mine is shipped, is about 26 miles distant from the mine. Connection is made with the Chesapeake & Ohio R. R. by a spur line . 8 miles in length, owned and operated by the company.

Jan 1, 1929

TULSA SECTION At the smoker concluding the two day meeting of the Tulsa section of the American Institute of Mining and Metallurgical Engineers, Tulsa, Okla., Feb. 26, 1919, Dr. Willis T. Lee, the new head of the Geological Department of the University of Oklahoma, was introduced to the assembled geologists and mining engineers. Dr. Lee requested that the geologists and engineers who were making a specialty of petroleum geology assist him in giving a good course in practical oil geology in the Geological Department of the University. After a motion offering the services of all present in giving lectures on their special subjects had been adopted, Dr. Perrine of Hutchinson, Kans., named the geologists who were pledged to give lectures in Dr. Lee's course. The students in geology at Norman are assured of the latest information regarding practical work in petroleum geology and will have the inspiration derived from contact with men who are actually at work upon the problems which they are studying. Dr. Lee and President Brooks of the University are to be congratulated upon the introduction of this .method of instruction. The plan thus put into operation is similar to the graduate system of coaching in athletics followed at many of the large universities; what is good for instruction in athletics should also prove good for instruction in applied geology.

Jan 6, 1919

LIST OF THE MEETINGS OF THE INSTITUTE AND THEIR LOCALITIES FROM ITS ORGANIZATION TO OCTOBER, 1904 Transactions Number Place Date Vol Page 1 Wilkes-Barre, Pa May, ?71 1 3 2 Bethlehem, Pa August, ?71 1 10 3 Troy, N Y November, ?71 1 13 4 Philadelphia, Pa February, ?72 1 17 5 New York, N Y May, ?72 1 20 6 Pittsburg, Pa October, ?72 1 25 7 Boston, Mass February, ?73 1 28 8 Philadelphia, Pa May, ?73 2 3 9 Easton, Pa October, ?73 2 7 10 New York, N Y February, ?74 211 11 St Louis, Mo May, ?74 3 3 12 Hazleton, Pa October, ?74 3 8 13 New Haven, Conn February, ?75 3 15 14 Dover, N J May, ?75 4 3 15 Cleveland, 0 October, ?75 4 9 16 Washington, D C February, ?76 4 18 17 Philadelphia, Pat June, ?76, 5 3 18 Philadelphia, Pa October, ?76 5 9 19 New York, N Y February, ?77 5 27 20 Wilkes-Barre, Pa May, ?77 6 3 21 Amenia, N Y October, ?77 6 10 22 Philadelphia, Pa. May, ?78 6 18 23 Chattanooga, Tenn May ?78 7 3 24 Lake George, N.Y. Oct. ?78 7 25 Baltimore, Md. Feb. ?79 7 26 Pittsburgh Pa, May ?79 8

Jan 1, 1923

LIST OF THE MEETINGS OF THE INSTITUTE AND THEIR LOCALITIES FROM ITS ORGANIZATION TO OCTOBER, 1904 Transactions Number Place Date Vol Page 1 Wilkes-Barre, Pa May, ?71 1 3 2 Bethlehem, Pa August, ?71 1 10 3 Troy, N Y November, ?71 1 13 4 Philadelphia, Pa February, ?72 1 17 5 New York, N Y May, ?72 1 20 6 Pittsburg, Pa October, ?72 1 25 7 Boston, Mass February, ?73 1 28 8 Philadelphia, Pa May, ?73 2 3 9 Easton, Pa October, ?73 2 7 10 New York, N Y February, ?74 211 11 St Louis, Mo May, ?74 3 3 12 Hazleton, Pa October, ?74 3 8 13 New Haven, Conn February, ?75 3 15 14 Dover, N J May, ?75 4 3 15 Cleveland, 0 October, ?75 4 9 16 Washington, D C February, ?76 4 18 17 Philadelphia, Pat June, ?76, 5 3 18 Philadelphia, Pa October, ?76 5 9 19 New York, N Y February, ?77 5 27 20 Wilkes-Barre, Pa May, ?77 6 3 21 Amenia, N Y October, ?77 6 10 22 Philadelphia, Pa. May, ?78 6 18 23 Chattanooga, Tenn May ?78 7 3 24 Lake George, N.Y. Oct. ?78 7 25 Baltimore, Md. Feb. ?79 7 26 Pittsburgh Pa, May ?79 8 28 Montreal, Canada Sept, ?79 8

Jan 1, 1923

By H. W. McCue, Henry Rogatz

Oil.—In the Texas Panhandle, 502 oil wells were drilled during the year 1940, with a total daily initial production of 139,187 bb1.—that is, 137 more oil wells drilled than in the previous year, with an increase in total daily initial production of 8219 bbl. The total daily potential of the field on Dec. 31, 1940, as determined by the Texas Railroad Commission, was 1,375,502 bbl., an increase of 30,825 bbl. over the previous year. On Dec. 31,1940, a daily allowable of 85,050 bbl., which was a decrease of 35 per cent over 1939, was assigned to the field to be produced from 4788 wells. The total amount of oil produced for the year was 26,788,590 bbl., making a cumulative total of 378,960,728 bbl. during the past 19 years. No new oil-producing acreage was discovered. Gas.—During the year, 92 gas wells were drilled, having a combined open flow of 2,402,900.000 CU. ft.; that is, 6 more than the number of wells drilled in 1939, with an increase in the open flow of 204,900,000 cu. ft. per day. The gas production for the year was 670,435,112,000 CU. ft., and the total gas removed from thc ground during

Jan 1, 1941

LIST OF THE MEETINGS OF THE INSTITUTE AND THEIR LOCALITIES FROM ITS ORGANIZATION Transactions Number Place Date Vol Page 1 Wilkes-Barre, Pa May, ?71 1 3 2 Bethlehem, Pa August, ?71 1 10 3 Troy, N Y November, ?71 1 13 4 Philadelphia, Pa February, ?72 1 17 5 New York, N Y May, ?72 1 20 6 Pittsburg, Pa October, ?72 1 25 7 Boston, Mass February, ?73 1 28 8 Philadelphia, Pa May, ?73 2 3 9 Easton, Pa October, ?73 2 7 10 New York, N Y February, ?74 211 11 St Louis, Mo May, ?74 3 3 12 Hazleton, Pa October, ?74 3 8 13 New Haven, Conn February, ?75 3 15 14 Dover, N J May, ?75 4 3 15 Cleveland, 0 October, ?75 4 9 16 Washington, D C February, ?76 4 18 17 Philadelphia, Pat June, ?76, 5 3 18 Philadelphia, Pa October, ?76 5 9 19 New York, N Y February, ?77 5 27 20 Wilkes-Barre, Pa May, ?77 6 3 21 Amenia, N Y October, ?77 6 10 22 Philadelphia, Pa. May, ?78 6 18 23 Chattanooga, Tenn May ?78 7 3 24 Lake George, N.Y. Oct. ?78 7 25 Baltimore, Md. Feb. ?79 7 26 Pittsburgh Pa, May ?79 8 28 Montreal, Canada Sept, ?79 8 29 New York, N.Y. Feb, ?80 9

Jan 1, 1923

Trans No. Place Date Vol. 1. Wilkes-Barre, Pa' May, '71 1 2. Bethlehem, Pa Aug., '71 1 3. Troy, N. Y Nov., '71.. 1 4. Philadelphia, Pa Feb., '72.. 1 5. New York, N. Y.' May, '72.. 1 8. Pittsburgh, Pa Oct., '72.. 1 7. Boston, Maas Feb., '73.. 1 8. Philadelphia, Pa." May, '73.. 2 9. Easton, Pa Oct., '73.. 2 10. New York, N. Y Feb.. '74.. 2 11. St. Louis, Mo.* May, '74.. 3 12. Hazleton, Pa Oct., '74.. 3 13. New Haven, Conn Feb., '75.. 3 14. Dover, N. J. ? May, '75.. 4 15. Cleveland, 0 Oct., '75.. 4 16. Washington, D. C Feb., '76.. 4 17. Philadelphia, Pa.} June, '76.. 5 18. Philadelphia, Pa Oct., '76.. 5 19. New York, N. Y Feb., '77.. 5 20. Wilkes-Barre, Pa. ? May, '77.. 8 21. Amenia, N. Y Oct., '77, . 6 22. Philadelphia, Pa Feb., '78:. 6 23. Chattanooga, Tenn.*...May, '78'.. 7 24. Lake George, N. Y Oct., '78.. 7 25. Baltimore, Md.* Feb., '79.. 7 26. Pittsburgh, Pa Mayo '79.. 8 27. Montreal, Canada Sept., '79., 8 28, New York, N. Y.? Feb., 'SO.. 8 29. Lake Superior, Mich. ..Aug., '80.. 9 30. Philadelphia, Pa.' Feb., '81.. 9 31. Staunton, Va May, '81..10 32. Harrisburg, Pa Oct., '81..10 33. Washington, D. C.? ....Feb., '82..10 34. Denver, Colo Aug., '82..11

Jan 1, 1928

By Henry Rogatz, H. W. McCue

Oil.—In the Texas Panhandle, 502 oil wells were drilled during the year 1940, with a total daily initial production of 139,187 bb1.—that is, 137 more oil wells drilled than in the previous year, with an increase in total daily initial production of 8219 bbl. The total daily potential of the field on Dec. 31, 1940, as determined by the Texas Railroad Commission, was 1,375,502 bbl., an increase of 30,825 bbl. over the previous year. On Dec. 31,1940, a daily allowable of 85,050 bbl., which was a decrease of 35 per cent over 1939, was assigned to the field to be produced from 4788 wells. The total amount of oil produced for the year was 26,788,590 bbl., making a cumulative total of 378,960,728 bbl. during the past 19 years. No new oil-producing acreage was discovered. Gas.—During the year, 92 gas wells were drilled, having a combined open flow of 2,402,900.000 CU. ft.; that is, 6 more than the number of wells drilled in 1939, with an increase in the open flow of 204,900,000 cu. ft. per day. The gas production for the year was 670,435,112,000 CU. ft., and the total gas removed from thc ground during

Jan 1, 1941

ALEXANDER BRYDEN Alexander Bryden, clean of engineers in the anthracite mining field, and a member of the pioneer Pittston family, was claimed by death Wednesday, September 26, 1917. The announcement was not a surprise, as he had been in a critical condition for several days. Mr. Bryden had been in failing health for a year past, but his indomitable will kept him at his accustomed duties until quite recently. Two weeks before his death he attended the regular weekly meeting of the Board of Directors of the Miners' Savings Bank in Pittston, Pa. At that time he apparently felt that his end was fast approaching, as he bade farewell to his associates on the bank board. Until a few days before the end, he continued to give attention to business matters at his home, in preparation for the end, which he met unflinchingly. In the passing of Mr. Bryden, northeastern Pennsylvania loses one of the best-known mining engineers, and the community, a man who, throughout his long life, was actively interested in its social welfare and business prosperity. He was for many years prominent in the management of the mining operations of the Pennsylvania Coal Co., and at the time of his death held the position of consulting engineer of the Pennsylvania and Hillside Coal. Companies.

Jan 12, 1917

The high-grade orebody at Miami was mined successively by top-slicing, shrinkage, stoping and under caving. The method described in this paper was developed to enable the low-grade orebody (36,000,000 tons assaying 1.06 per cent copper) to be mined at a low cost without further dilution of the grade. The method is clearly described and illustrated by drawings and photographs, and the original paper should be consulted as it is impracticable to abstract it, beyond noting that the mining cost is just under 40 cents per ton and the average grade of ore now being produced yields less copper than the mill tailing of 1915, the tons mined per day having increased from 4000 to 18,000 in the same period. Vertical and Incline Shaft Sinking at North Star Mine By Arthur B. Foote, Grass Valley, Calif. (Tech. Pub. No. 324: Class A. Metal Mining, No. 36) THE main shaft of the North Star mine is an inclined one following the main vein at an average dip of 26 deg., a vertical shaft intersects it at the 4000-ft. (incline) level, the incline continuing to the 6300-ft. level. At this point the vein was found to give out and a new vein, called the No. 1, was found to dip in exactly the opposite direction.

Jan 1, 1930