On August 19th, 1871, on the north side of the east heading, machine No. 1, starting at 10 A. M., had at 2.08 P. M. drilled three holes, averaging about five feet four inches; the time actually occupied in drilling being 74 minutes, or an average of about 25 minutes to each hole. The remaining 2 hours and 54 minutes are accounted for by changes of drills, breaking of carriage, and an interval of 40 minutes for dinner. On the south side, machine No. 2, starting at 9.35 A. M., had at 2.09 P. M. drilled three holes, averaging about six feet four inches; the time actually occupied in drilling being 81 minutes, or an average of 27 minutes to each hole. The remaining 3 hours and 13 minutes are accounted for in a similar manner to the time of machine No. 1, except that there was no accident to the carriage. The average time of the two machines was about 26 minutes for the average depth of about five feet ten inches, being two inches and seven-tenths per minute. It will be seen by these facts that the actual drilling is but a comparatively small part of the work; bringing forward the machines, connecting to the air main, inserting the drills into the jaws of the machine piston, changing these drills as they wear down, oiling, releasing drill when stuck, removing back the machine carriage out of reach of the blasted rock, waiting for blaster to charge the holes, connect his wires, and apply the electric current to fire the exploders, removing the debris to clear the track for the approach of the drills—all these operations, so varied and yet so necessary, each consume a considerable quota of the eight hours allotted to each shift. On August 30, 1871, a blast was made in the east heading at 5.30 P. M., as follows: fourteen 7 foot holes were fired with 25 lbs. of Nitro-Glycerin, throwing out about 30 tons of loose rock; and one solid rock, diameter 9 × 4½ × 4 feet, and weighing about 24,000 lbs., a distance of 30 feet, a weighty testimonial to the explosive power of Nitro-Glycerin. The expense incurred and difficulties met with, in working at the Central Shaft, will serve as a hint to contractors to make all due allowance in their estimates for striking a seam of water; work may go on smoothly for a long time; the general geological formation of hill or mountain may be well understood, and yet the contractor cannot tell but that he may strike a vein of quartz that may throw him back days and weeks in his drilling calculations, or a seam of water which will cost him thousands of dollars in machinery and labor to keep it under.