it can be advantageously run into an open stope. . Sullivan, Ingersoll-Sergeant, and Rand air drills are used in mining, and all give satisfaction. In the wider stopes and in hard rock as well as in drift work, a 3 inch machine is employed, requiring two men for its operation. In raises and in softer ground or narrow stopes, a drill with 2-inch or 24-inch piston is used, one man alone operating such sizes. These small sized drills are known to the miners as "Babies" and "Chippies." The following brief description of the practice in mining in the Cripple Creek district is taken from the Professional Paper on the Geology and Gold Deposits of the Cripple Creek District, Colorado, by Waldemar Lindgren, and F. L. Ransome:1 "The methods of mining employed at Cripple Creek, are not materially different from those in use in other districts, where metalliferous veins are exploited. Overhand stoping with slightly differing variations is used. In narrow veins, short stulls comprise about the only timbering used and required, but when the stopes become over 12 feet wide, square sets become desirable. The rock is usually so hard that stopes will stand unsupported for a remarkable height and width. Examples of stopes up to 200 feet high and 30 feet wide, standing without any support may be seen at the Vindicator and Prince Albert mines. Still in many places the calcite seams cause a dangerous scaling off on the walls, and partial filling must be resorted to in conjunction with the square sets. In the big stopes up to 50 feet wide, as in the Portland mine, from 30 to 40 per cent of the amount broken can be left in the mine as filling. "A favorite method of stoping is to break down the whole of the ore in place between two levels, leaving the loose rock to be drawn off through shoots as rapidly or slowly as may be required. This leaves the empty stope entirely unsupported. Sometimes the walls are partly secured by stulls while the ore is being drawn off. The ordinary half or three-fourths ton cars are used. The El Paso is the only mine in which 1-ton cars have been introduced and hoisted on cages. Buckets are also employed very extensively in the shafts and sometimes used to a depth of even 1,000 feet, a practice which is not to be recommended. Practically all of the shafts are perpendicular." The problem of working very narrow high-grade veins is a difficult one and has led to the adoption of the system known as "resuing.' There is, however, a question regarding the use of resuing and the 1 U. S. G. S., Professional paper No. 54, pp. 135, 136, 1906. 1 working of the vein and adjoining rock walls together. According to F. C. Roberts 1 the two methods gave results that varied considerably when applied under the following conditions: "When resuing was applied, the vein was first stripped on the foot wall (which, in this case, was the more economical to handle) to a width of 30 inches. This waste rock used largely as filling, although a certain percentage was necessarily sent to the surface. When some 3,600 square feet of quartz had been stripped, this was broken down as a clean product so that no sorting was required. "In the second case, the quartz and adjoining rock were broken together and the fineness to which this product was reduced allowed of sorting out only 5 per cent of the barren rock." There was considerable difference in the profit and loss obtained in operating by these two methods, but the results favored resuing. Wide Veins. California: the Utica Mine, Mother Lode. - Mining practice on the Mother lode is given in a valuable paper by J. H. Collier in which the particular conditions encountered there with the manner in which they have been met are given in detail. "It might more properly be called a gold-bearing mineralized zone rather than a simple vein. The zone consists of a large mass of crushed diabase which, under pressure, has developed a slaty cleavage. The crushed mass has been more or less altered into a schist containing considerable mariposite and white mica. In this mass the ore occurs as large bodies of massive quartz of a brownish-grey color; as masses of quartz veins from 1 to 3 inches wide, interspersed with micaceous schists in a distinctly banded structure; as masses of more or less altered diabase, containing infiltrated silica often in reticulated veinlets; and as impregnations in massive diabase; all containing free gold and auriferous pyrites. "In working upward on the ore-bodies, they sometimes change from massive quartz to a schistose character, and thin out toward the hanging-wall. Cross-cuts run into the foot-wall, then show the ore making next the foot-wall, and soon widen out to the original width on its upward course, thus proving that the ledge was cut off by a large horse of diabase split from the hanging-wall and fallen to the foot-wall. In this way, the ore-body is made up of several parallel lenses or masses, at different points dipping at a high angle to the eastward with a greater southerly pitch, ranging in all from 10 to over 100 feet in width. 1 Eng. and Min. Jour., Vol. 76, p. 882, 1903. 2 T. A. I. M. E., California Mines and Minerals, pp. 97, 98, 105-109, 1899. "With this outline of the general nature of the deposit, the difficulties of mining, more particularly stoping, such a deposit will be better understood. Not only must the stopes be properly supported and economically worked, but the ground must be thoroughly prospected as the work proceeds. "The prospecting must be thorough to ensure the most economical use of the long levels through which the ore is removed. These levels are often driven in extremely hard diabase, and are not only costly in driving and fitting with tracks and compressed-air pipes, but are often very expensive and difficult to keep open, on account of the settling and crushing of the rock. "A stope is started by breasting-out the ore to the full width of the deposit. Cross-cuts are run into both walls, to be sure that all the ore has been removed. The opening is then timbered with 8-foot stope sets. If the ground is solid, no timbering is done, until the whole mass of the rock covering the area of the stope has been removed. The posts are then set in the solid rock, with 6-inch spreaders and 12-inch round brace-sprags between the posts at the bottom. A floor is then laid over the spreaders. "If the rock is loose or soft, one set is put in at a time as fast as room is made for them. In the soft ground heavy sills are laid, to give a solid foundation for the posts. Sills are not, as is generally supposed, an advantage in working up under an old stope. Good floors laid across the spreaders, even though they have been in place so long as to be badly decayed, are found to be more serviceable than sills. The sills are seldom in place when reached, and have to be caught up securely, or they are liable, by their own movement, to start a serious run in the waste above them. After the sill floor is opened and timbered, a raise following the foot-wall is run up to the level above. "This raise is necessary for the proper ventilation of the stope, as well as the economical introduction of timber and waste into the stope; the timber and waste being thrown down the raise into the stope. The raise is located in the most convenient part of the stope, and, if possible, where there is a seam of gouge on the foot-wall, which greatly lessens the cost of the work by lessening the difficulty of breaking the ground. If the rock 3 hard and solid, machines are used, and the raise is timbered with full-sized stope sets, if timbering is necessary; so that, as the stope is carried up, the timber of the stope is joined on to that of the raise. If the ground is loose, the work is all done by hand, and the raise is built up solid with round timber, |