As a check on the average figures obtained from various sources, the following estimate of the cost of drilling per cubic yard was made up from these average figures, for comparison with the actual average cost on the whole work. The cost records show this to be about $2.25 per yd., exclusive of power for running the drills, almost exactly what the following estimates give for theoretical average conditions, although no effort was made to have this latter compare so closely. _Estimated Cost per Drill per Day._ Drill Runner 1 at $3.50 per day, $3.50 Helper 1 ” 2.00 ” ” 2.00 Nipper 1/5 ” 1.75 ” ” 0.35 Heading foreman 1/12 ” 5.00 ” ” 0.42 Walking boss 1/50 ” 7.50 ” ” 0.15 Blacksmith 1/12 ” 4.00 ” ” 0.34 Blacksmith helper 1/12 ” 2.00 ” ” 0.16 Machinist 1/12 ” 3.00 ” ” 0.25 Machinist helper 1/24 ” 1.75 ” ” 0.07 Pipe fitter and helper 1/50 ” 5.00 ” ” 0.10 Oil, waste, blacksmith coal, etc. 0.24 Drill steel, 6 in. per shift 0.20 ----- $7.78 Average number of feet drilled per cubic yard 3 to 3.5 Number of feet drilled per drill, per shift 10.5 to 12 Number of yards per drill, per shift 3.5± Cost of drilling, per yard, $7.78/3.5 $2.22± In all the foregoing tables and computations, the quantities used have been those paid for. The quantity taken out, however, has been 10% more than that paid for, and 28% more than the contractor was actually required to take out. The specifications required that the excavation should be taken entirely outside of the neat line, as shown on Plate VIII of the paper by Mr. Jacobs, but not necessarily beyond this line, but that the contractor would be paid for rock out to the standard section line, which is 1 ft. larger on the sides and top and 6 in. deeper in the bottom than the neat line. A great deal of the extra quantity was due to rock falling from the core-wall side whenever one working face was behind the other. Blasting at the face behind generally loosened more or less rock on the core-wall side of the tunnel which was ahead, in one or two instances breaking entirely through, as shown in Fig. 2, Plate XXVI, the hole in the core-wall in this case being utilized by building a storage chamber in it.