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By Richard M. Foose

FIVE miles southwest of Mt. Holly Springs, Cumberland County, Pennsylvania, the Philadelphia Clay Co. has been mining and milling a white clay since 1896; for use in white cement, as a filler in rubber, pigment and paper, in the manufacture of insecticides, and for other minor purposes. Until late in 1942, when the mine was abandoned because of labor shortage, combined underground mining and surface stripping produced approximately 30,000 tons of clay a year, of which 10,000 tons were refined in the mill. GEOLOGY Lower Cambrian Antietam quartzite and the Montalto quartzite, stratigraphically older, trend N.55°E. and make a sharp 1600-ft. anticlinal ridge of the South Mountains. The Tomstown dolomite overlies the Antietam quartzite on the southeast flank of the anticline, which is displaced near its crest by a steeply dipping oblique fault. Erosion of the less resistant Tomstown formation has resulted in a narrow valley at an elevation of 700 ft. Directly on top of the Antietam quartzite and at the base of the Tomstown formation is a zone of sandy white clay, lenticular along the strike of the formations, ranging in thickness from 10 to 300 ft. within a mile. All of the formations dip steeply to the southeast, from 65° to vertical. The clay crops out at an elevation of about 1000 feet. ORIGIN AND CHARACTER The uppermost part of the Antietam formation is sericitic and schistose at many places, and at all these places weathering is in an advanced stage. The clay is the residual product of weathering of this sericitic quartzite or sandy schist. The crude clay has the physical aspect of a sandy kaolin, but there are large areas in the clay formation that are low in free silica, and commonly the 30 ft. adjacent to the Antietam quartzite is notably free of silica. The overlying Tomstown dolomite has been weathered almost completely to a mixed yellow and brown clay, which carries a zone of nodular and chunky limonite and manganese ore, 4 to 12 ft. thick, about l00 ft. from the contact with the white clay. In mining, this zone is an important "marker," indicating where the white clay may be expected in an advancing tunnel. The contact of the white clay formation with the yellow and brown clay of the Tomstown formation is relatively sharp, although the line of contact is irregular and therefore responsible for the lenticular character of the white clay formation. Following is an analysis of the refined clay containing less than one per cent of moisture when dried at 212°F.: Si02, 67.05 per cent; A1203, 22.27; Fe203, 0.40; CaO, 0.00; Ti02, 1.05; MgO, 0.52; Na20, 0.04; K20, 0.88; ignition loss, 7.65; total, 99.86.

Jan 1, 1944

By Frank Riddle

PRODUCTS made from the ores of the sillimanite group, and synthetic substitutes for them, have unique properties, and service tests prove that they are playing, and will continue to play, a major part in improvements in metallurgical processes. Also, they are examples of how comparatively useless, rare, or "museum" minerals have been made available in commercial quantities. Until research developed uses for them, the minerals had been observed only in small, scattered masses, or crystals. Improvements in ceramic processes and compositions have come about very gradually. In the last 10 or 15 years, several outstanding developments have been made. Of greatest interest to the mining and metallurgical engineers are those affecting the composition, necessitating the mining of new minerals, and improvements in ceramic products used in metallurgical processes.

Jan 1, 1932

By Richard W. Smith

THERE are three distinct varieties of phosphate rock, in Tennessee, known commercially as: (a) the "brown" rock, which is the residual pro- duct of the weathering and natural concentration of certain phosphatic Ordovician limestones; (b) the "blue " rock, which is an unaltered phosphatic stratum of Mississippian or Devonian age; and (c) the "white" rock, which is the result of chemical replacement and deposition. Before 1894, South Carolina and Florida had supplied most of the phosphate of the United States, South Carolina leading until that date and Florida from then until the present time. In December, 1893, the blue phosphate of Tennessee was discovered almost simultaneously on Swan Creek, in Lewis County, by two independent parties-by one as the result of a careful and systematic search for a workable deposit of the long known kidney phosphate, and by the other through mistaking it for a "bloom" of coal. Leases were taken and, with further prospecting disclosing other deposits in the region, the development progressed as rapidly as 'could be expected without railroad transportation

Jan 1, 1924

By R. J. Grissom

PHOSPHATE deposits have been worked in many countries of central and south central Tennessee, but only ht ebrown rock deposits of Maury and Giles Counties will be discussed at any length in this articles, as all of the major opeations are now located there. They are: Mt. Pleasant District-Federal Chemical Co., Hoover and Mason Phosphae Co., International Minerals and Chemical Corp. (Maury and Giles Counties), Virginia-Carolina Chemical Corp. (formerly Charleston Mining Co.), and Victor Chemical Co. Columbia District-Armour Fertilizer Works and Monsanto Chemical Co. In the near future, the well-known, extensive deposits of blue rock in Lewis and Hickman Counties,also the brown rock in Hickman, Willamson, Summer and Davidson Counties, will again come into production. Certain physical peculiarities of the Tenessee deposit have played an important part in the design and use of mining and milling equipment.

Jan 1, 1944

By W. H. Moore, E. T. Powell

IN the early days of mining in the Anthracite field, only the thicker and better seams of coal were mined, because of the limited mining and coal-cleaning facilities, therefore many of the thinner and less productive seams were permitted to remain unmined. With improvements in mining methods, the introduction of modem preparation plants, and the increased market demand for small-size coal, the thinner and more laminated seams have now become assets. In many instances these seams overlie the mined-out beds of the thicker and better seams, from which all recoverable coal was removed by the conventional breast-and-pillar method of mining. Some collieries in certain sections of the Anthracite field are now relying on these thinner and laminated seams. For the purpose of illustration, a large area in the Hickory Swamp-Ridge Basin of the western middle coal field has been selected, where as early as 1898 the No. 4, or Little Buck Mountain, seam was mined and pillars removed. The No. 5, or Buck Mountain, seam lying on a comparatively light pitch and with intervening strata of but 55 ft. of rock was not mined until 1935. Farther east, in the same basin the Nos. 8 and 9 seams, which are two splits of the Mammoth seam, have been mined and robbed and the workings have been abandoned since 1896. The overlying No. 9 ¾ seam, or the upper split of the Mammoth, and the No. 9 ¾ or 4-ft. seam remained virgin, with only an interval of 50 ft. of rock separating them, and with 40 to 50 ft. of rock strata separating the No. 9 ½ seam from the completely mined area of the Nos. 8 and 9 seams. These seams lie on a pitch of 45° on the south side of the basin and on 75° on the north side of the basin. Mining has been carried on in the 9 ½ and 9 ¾ seams for 3 years on both dips of the basin, for a distance of 3500 ft. In some sections the overlying strata of the thicker seams previously mined have settled without any apparent breaks in the upper strata, as indications have shown in the top split of the Mammoth; while in other areas the roof and bottom of this top split of the Mammoth have settled unevenly, thereby causing the bottom and roof to break into blocks. In attempting to mine over a large area of the No. 5 or Buck Mountain seam, a similar settlement has been encountered; the roof of the seam has been broken and a considerable amount of timbering has been necessary in order to make the mining of the seam possible. The conventional breast-and-pillar method, using shaker conveyors, has been used in the No. 5 seam, and a slant-breast method in the mining of Nos. 9 ½ and 9 ¾ seams. MINING OF LIGHT-PITCH SEAMS The No. 4 seam was mined and robbed by the conventional breast-and-pillar system. In this area the seam pitched from 5° to 25° on the north dip, averaged 8 ft. in thickness and had a slate bottom and a

Jan 1, 1941

By Henderson, Robert

A GOOD idea of the magnitude of the underground operations at Climax can be gained from the following figures. A little more than 43,000,000 tons has been drawn from the mine and of this amount, 40,500,000 tons has been drawn in the past ten years and 12,000,000 tons was drawn in two of the war years. The maximum daily average output over a period of one month was slightly more than 20,000 tons but during this period, production on certain days was 24,000 tons, and 9000 tons was produced in a single eight-hour shift. This production came chiefly from 260 draw points although all of them were never in operation at one time. The haulage system for these draw points is made up of 7.5 miles of 36-in.-gauge track, and 131,000 ft. of subsidiary drifts and 44,000 ft. of raises have been driven to develop the necessary broken ore reserves for this high production. Power consumption is often considered an index of operating efficiency. In 1943, the year of maximum production, the mine power consumption was 19,223,000 kw.-hr. or 3 kw.-hr. per ton; in 1945 it was 3.5 kw.-hr. per ton. To handle this amount of power, there are four transformer stations and one switch station in the mine. Mr. Garrabrant, the chief electrician, describes the electrical installation in this issue.

Jan 1, 1946

By William G. Brissenden

Gaspe Copper Mines Ltd., a subsidiary of Noranda Mines Ltd., operates a completely integrated copper mining, milling and smelting plant at Murdochville, on the Gaspe Peninsula of Quebec. Operating six days a week, the mine produces 8000 tpd of ore. The mill runs continuously and capacity is rated at 6500 tpd of ore. Treating Gaspe concentrate output plus a certain amount of custom concentrate, the smelter produces between 3700 and 4000 tons of copper anodes per month.

Jan 9, 1959

By R. R. Van Valkenburch

IT has always seemed to me that mining methods are inventions that follow necessity. I have yet, to be connected with a property where the consultant who has been engaged has laid out a mining method that has been strictly adhered to through the life of the mine. Possibly there are exceptions. As a general rule, perhaps, the method becomes the result of sad experience. I suppose if a person were to attempt to measure the tendency to get away from shrinkage stoping, he would need to send out a questionnaire and expect to receive truthful answers, and, having compiled the results, I think we would find that throughout the country there would be but few cases where present value of product permits the old original so-called shrinkage method to be followed. The method that I had hoped to hear Mr. Fozard expound is strictly an adaptation of shrinkage. Cav-ings do not enter. It was developed by Mr. Fozard and his staff at the Beatson mine of the Kennecott Copper Corp., at, Latouche, Alaska. Stephen Birch, in the TRANSACTIONS in 1923, submitted a brief paper on the mining at Beatson. He stated that a new adaptation of shrinkage was being tried because, although at sur-face the copper .content had been relatively high, at lower levels, in the mine it had decreased.

Jan 5, 1927

By F. D. Waltman

Under the hot, baking sun, engineers at the AEC's Nevada Test Site have been busy for several years in the sinking of 48-in. diam shafts to depths varying anywhere from 1800 to 4800 ft below the surface. In so doing these men have evolved several new techniques which should be of interest to the mining industry. Surface Facilities Designed For Speed: "Expediency plus efficiency" is a key phrase at the Site. Because of the relatively short duration of actual mining operations, all equipment has been packaged to decrease time and cost of "set up" and "take down". The headframe, designed specifically for use over 48-in. cased shafts, can be erected or dismantled within 48 hours. The back legs are pinned and hinged to the front legs for ease of installation and, when dismantled, for movement to another site with a minimum of delay.

Jan 6, 1966

SUMPEARY OF CURRENT PRACTICES History The outcrop and surrounding area of Comincots Sullivan Mine was originally mined by small open cuts on surface and small open stopes underground to which shafts and adits were driven for access. When it was established that a commercial grade of ore was available, an adit was driven on the 4600 level (feet above sea level), and OM was extracted by larger scale open stoping leaving supporting pillars where necessary. After the depth of the ore body was proven to the 3900 level and an adit driven at this level, many miles of drifts, crosscuts, raises and sublevels were driven for the extraction of the ore above this level. Larger open stopea were extended from this development. The mining method was, and to a very limited degree still is, a benching method. Due to the strong hanging wall in this area of the mine, stopes with a width of 100 feet or more were opened. In 1931, because the orebody was proven to extend below the 3900 level, a winze was sunk from the 3900 level to the 3350 level. From this winze three intermediate levels were opened. Following a plan of development well in advance of production requirements, further sinking was done by winzes and eventually a large shaft was raised to surface. Prior to 1958 the 2850 level was bottom which since that time has been extended to the 2500 level. Open stopes were developed and mined as this area was opened up.

Jan 1, 1970

By H. H. Wade, N. F. Schulz

The large quantities of iron-bearing materials, including taconite, semi-taconite,* and other low-grade ferruginous materials occurring in Minnesota and elsewhere, constitute an important potential source of iron. Satisfactory grade and recovery of iron ore concentrate cannot ordinarily be obtained from these ferruginous materials by simple methods of beneficiation. Iron is distinctive in that the free metal and two of its oxides [magnetite (Fe2O3) and maghemite (gamma-Fe2O3) ] are strongly ferromagnetic. The successful magnetic separation of natural magnetite from taconite has already been established on a commercial scale. The iron in semi-taconite, however, occurs largely as goethite (Fe2O3-H4O) and hematite (Fe2O3) which do not respond to ordinary magnetic separation methods. Magnetic roasting converts these iron oxides to magnetite, which can, after liberation, be magnetically concentrated. MAGNETIC ROASTING Hematite undergoes a stepwise reduction when exposed at moderately elevated temperatures to a reducing atmosphere containing hydrogen or carbon monoxide: Fe2O3? Fe3O4 ? FeO ? Fe Since the desirable product in magnetic roasting is Fe3O4, the conversion is halted after the first stage by controlling the reduction potential of the gas mixture with water vapor or carbon dioxide. The reducing gas mixture must be such that the oxygen partial pressure at the solid-gas reaction interface will be maintained intermediately between the oxygen partial pressures in equilibrium with Fe2O3 and Fe3O4 at the prevailing temperature. Because of the rapid increase in decomposition pressure of Fe3O4 with increase in temperature, the practical upper limit of useful reaction temperature is about 1400°F, above which over-reduction usually occurs in atmospheres containing hydrogen or carbon monoxide. On the other hand, useful reaction rates usually occur only above 800°F. Goethite reacts similarly except that the combined water probably has to be driven off thermally before the reduction to magnetite occurs. Iron carbonate must also be decomposed thermally to an oxide before conversion to magnetite. Iron silicates are apparently not amenable to magnetic roasting. The rate of penetration of the reaction toward the interior of a given ore fragment is dependent on the chemical composition and physical structure of the solid. Most ore fragments tested here reduced satisfactorily to 1/4-in. depth in less than 14 min at 1200°F. Some very dense fragments, however, were reduced to less than 1/32-in. depth under the same conditions. Determination of the optimum temperature, gas composition, ore fragment size, or time of exposure

Jan 1, 1961

Among the bills now pending in Congress is one to authorize exploration for and disposition of coal, phosphate, sodium, oil, oil shale, and gas on, public domain. One, to provide protection and government revenue for potash and for zinc ores and products. One to prevent withdrawal of mineral lands from entry and occupancy by law, also to promote, production of quicksilver, tungsten, sulfate, pyrites, and sulfur, and of manganese and manganiferous ores. Three resolutions have been introduced to suspend requirements of annual assessment work on mining claims during year 1919 and one to relieve owners of mining claims mustered into military service.

Jan 8, 1919

Coal Division Industrial Minerals Division Minerals Beneficiation Division Mineral Economics Division Mineral Industry Education Division Mining, Geology and Geophysics Division MINING BRANCH AND DIVISIONS OFFICERS AND COMMITTEES Council Ralph E Kirk, '55, Chairman (Coal). C M Cooley, Secretary, M D Cooper, '56 (Coal), Harold Bannennan. '55 (Ind Min Div ). R C Stephenson, '56 (Ind Min Div ) , E P Pfleider, '55 (MGGD) . J D Forrester. '56 (MGGD) , Donald W Scott, '55 (MBD). S D Michaelson, '56 (MBD). J K Richardson (MED). J R Van Pelt, Jr (MIED) COAL DIVISION Established as a Division September 20, 1929 M D Cooper. Chairman H F Yancey, Chairman-elect David R Mitchell, Secretary-Treasurer Professor of Mining The Pennsylvania State University State College. Pennsylvania

Jan 1, 1954

Coal Division Mineral Industry Education Division Industrial Minerals Division Minerals Beneficiation Division Mineral Economics Division Mining, Geology and Geophysics Division Council R C Stephenson, Chairman (Ind Min Div), M D Cooper (Coal), H F Yancey (Coal), S D Michaelson (MBD), Will Mitchell, Jr (MBD), J R Van Pelt, Jr (MIED), S S Cole (Ind Min Div), J D Forrester (MGGD), L E Shaffer (MIED), E L Clark (MGGD), C W Merrill (MED), E H Robie, Acting Secretary, 29 West 39 Street, New York 18, New York

Jan 1, 1955

Coal Division Industrial Minerals Division Minerals Beneficiation Division Mining, Geology and Geophysics Division Council Will Mitchell, Jr, Chairman (MBD), Kenneth L Cook, Vice-Chairman (MGGD). Edward L Clark (MGGD), Raymond B Ladoo (Ind Min Div), Sandford S Cole (Ind Mm Div), Norman L Weiss (MBD), C T Hayden (Coal), H F Yancey (Coal), Clayton G Ball (MED), P De Bruyn (MIED), Arnold Buzzalini, Secretary, AIME, 29 West 39th Street, New York 18, N Y Mining Branch Advisory Committee Will Mitchell, Jr, Chairman, Grover J Holt, J B Morrow, J L Gillson, Edward G Fox, S S Cole, Roger V Pierce, Norman L Weiss. H C Weed. J R Van Pelt

Jan 1, 1956

By W. R. Atkins

THE Negaunee mine is at the east end of the Marquette Range, in the city of Negaunee, on the Upper Peninsula of Michigan. Iron ore was first discovered on this property in 1883 by diamond drilling. A shaft was sunk soon afterward, and the mine has been worked continuously ever since. The total shipments from 1887 to' Jan. 1, 1945, were 20,417,587 long tons. The mine was taken over by the present operators, The Cleveland-Cliffs Iron Co., in 1903. During the past four years, 1941 to 1944 inclusive, the property has produced an average of nearly a million tons a year, and has employed more than 400 men. GEOLOGY The ore body at the Negaunee mine lies in a large syncline dipping about 15° to the west, the ore coming to ledge at the east end of the trough. The ore occurs in the Negaunee formation of the middle Huronian age, which consists of ferruginous cherts and slates through which intrusions of diorite have occurred. Although these intrusions of diorite have an important bearing on the formation of ore on the range, they are not important in this ore body. Some faulting has taken place along the diorite intrusions, or dikes as they are called locally, and also other faults are known to exist across the formation. These faults do not complicate either mining or development of the ore body. The footwall consists of jasper underlain with Siamo slate; the hanging wall is jasper and ferruginous chert. Fig. I shows a typical cross section of the ore body. The ore body is quite regular, about 120 ft. thick in the middle of the syncline and thinning out toward both sides of the fold. Its width ranges from 400 to 800 ft., the average being about 600 ft. The footwall is uniform in dip and strike, but irregular lenses of ore often extend 50 to 75 ft. up into the overlying jasper capping. METHOD OF MINING Ore in the Negaunee mine has been mined by top slicing almost exclusively since 1903. This method of mining has been employed because it is especially adapted to the size and shape of the Negaunee ore body, and to the soft, sticky nature of the ore as well as the generally soft, broken jasper capping. Development The ore body has been developed from six different levels with intervals varying between l00 and 125 ft. On the average, the dip causes a horizontal offset of 350 ft. per level, and under these circumstances it has been necessary to carry on considerable development in rock to make available the ore lying along the north and east footwalls. This is not as disadvantageous as might be supposed, because of reduced pressure and the accompanying saving in maintenance costs. The development of the

Jan 1, 1946

By E. D. Gardner

WHEN the National Forests Were created, all lands embraced in their boundaries were exempted from all forms of entry, except mineral claims. Later, by Act of June 11, 1906, and as amended by Act of Aug. 10, 1912, provision was made allowing homesteads on areas chiefly valuable for agriculture and not necessary for the public use. Patents to mining claim in the Forests are granted the same as on land not in the Forests, irrespective of timber or other values. It is the policy to encourage the highest use of the Forests. As a business proposition, it is a good policy to have mines developed in the Forests. Their development in remote or inaccessible regions causes the country to be opened up and, in addition to the local market which the mines create, means of transportation are afforded to outside markets. No examination of mining claims is made until patent has been applied for, unless they are actively interfering with the administration of the Forest. In this case, an examination is made, and if there is evidence that the claims are being held in good faith they are in no way interfered with. Timber is never sold from a mining claim except with the consent of the claimant, or unless it is clearly shown, after an examination, that the claim is abandoned. In the case of fire-killed timber, which rapidly deteriorates by standing, a contract bond arrangement can be made for the sale of the timber which protects the interests of both the mining claimant and the government. The promiscuous locating of mining claims has in the past caused considerable trouble. It has been, and still is, the custom in some parts of the West to locate a mining claim when the surface rights of any particular area are desired, irrespective of the mineral character of the ground. This has been done to hold power sites, town sites, summer residences, springs, etc. When the, ground is desired for any of these purposes, what is known as a Special Use Permit will be issued at a nominal sum, to legalize the occupancy. In most instances, it is far cheaper to take out one of these permits than to do the annual assessment

Jan 7, 1914

Discussion of the paper of E: D. Gardner, presented at the Salt Lake meeting, August, 1914, and printed in Bulletin No. 91, July, 1914, pp. 1467 to 1471. H. V. WINCHELL, Minneapolis, Minn.-There are two questions I should like to ask: First, does the Department still adhere to the decision made in the East Tintic case? Second, does the Department require placer ground to he of such value that, in the opinion of the Forest Service employees, it will pay to work, before admitting the location to be valid? T. C. HOYT,* Ogden, Utah.-With reference to the first question: the Department does not hold to that decision, as it was reconsidered by the Secretary Of the Interior, and the Department is governed by the decision of the Secretary Of the Interior, on those points always. The Department of Agriculture makes no decision as to what constitutes a sufficient discovery. The mineral examiners simply report their findings and Opinions. These are transmitted to the chief of the field division of the General Land Office, who in turn transmits the reports to the Commissioner Of the General Land Office, who decides whether the report raises an issue requiring a hearing. If a hearing is ordered, expert testimony is given on the question of the discovery, as well as the evidence of practical people who operate in the vicinity of the claim in question. As to the extent of placer values considered sufficient to justify a location, my answer will need a little amplification. I couldn't answer it directly for the reason that sometimes people resort to placer claim location as a means of acquiring land for Other purposes than placer mining, which makes it absolutely necessary that the government give close attention to the question of whether good faith has been shown, as it is the evidences of good faith that largely determine whether a report adverse to a claim shall be made. That is a difficult point to cover sometimes. For instance, in the region I have recently visited there are some 17 miles of a valley, from ¼ to ¾ mile in width, all covered by placer locations. It is valuable stock-grazing land, and is stocked at the present time. It also contains a stand of timber, and is on the watershed of an important stream-important from the fact that it furnishes the water supply to government storage reservoirs, and to pending reclamation and Carey Act projects. In this case the placer claims will not be disturbed as mere locations. They will simply remain there, and there will be no action with reference to them until the claimant asks for patent or, before patent, begins to denude that watershed and remove that timber. Then the government would direct that the mineral experts go on to the ground, examine it, prospect it, and submit their report, with a view to seeing if

Jan 11, 1914

By J. C. Smock

THE primitive mode of mining clay by open workings, in which the overlying beds of earth (commonly termed the "bearing") were removed, and the clay then dug out by sinking shallow pits, is still the prevalent and almost universal mode of extraction. This is particularly true of our cretaceous and tertiary clays, which are generally earthy in character, and but slightly covered by drift and alluvium. The most accessible beds in many of our clay districts have been worked out, and clay miners are compelled to search for new outcrops, or to remove thicker beds of top dirt or bearing. Under this stimulus subterranean working, or mining proper, has been suggested. A brief notice of this new mode, as employed by Mr. Otto Ernst, near the head of Chesquake's Creek, three miles south of South Amboy, New Jersey, is here presented for your consideration. Previous to mining, the old mode of extraction, digging pits, was found to be too expensive, in' consequence of the heavy amount of top dirt and the excessively large amount of water in these overly-

Jan 1, 1875

By Fred McConnell

FROM beginning to end, the processes of coal stripping are of great interest. From the time the prospector enters upon the property to examine it and to prove it, until the coal is loaded into railroad cars, every step must be taken with careful thought and planning. In proving the merits of a prospective property, an examination and computation of the overburden is of almost equal importance to the determination of the extent and quality of the coal bed itself. Is the overburden hard, and will it require drilling and shooting? How many yards of it will have to be handled to produce a ton of coal? Will it remain in place when .put in the spoil bank, or will it spread and run back into the pit? Are the drainage problems serious, and what will it cost to handle the water? Does the coal have bad dips, and what will be the grades and curvatures for haulage? These are a few of the physical problems that confront the prospector, and they can be ascertained only by adequate and careful drilling and engineering of the property to be considered. The engineer is an ever-present necessity, not only in the prospecting but in the daily operation of the property after it has' been approved and developed. The first step in operation after the location of the tipple is the contouring of the surface to be stripped and the laying out of the pits for operation, having in view again adequate room for spoil, drainage, haulage and other problems. If the overburden is hard, as much of it is in the larger stripping areas, it must be drilled for shooting with churn or well drills, the holes continuing from the surface down to or near the coal bed. The location of these holes should be made, and marked with stakes, by the engineer, acting in conjunction with the shooting foreman. The usual practice is to drill holes 6 in. in diameter, although the present tendency is to increase the diameter of these holes so that they will hold, without springing, a larger charge of explosive. With the use of the old method of shooting, the holes were sprung or chambered several times with charges of dynamite, and in the cavity thus made, the explosive was placed, largely at the bottom of the hole; but with the use of liquid oxygen as an explosive, and with the later

Jan 1, 1931