For a description of the quarries at the Roosevelt dam see page 81. The stone for the upstream face was cut to make a 2-in. joint, no depth from the face specified, and the cost of cutting was as follows:
Stone cutters helpers...................
... 15,502 hours
This force cut the stone for 98,575 sq. ft. of face area, at a cost, including supervision and tool sharpening of $0,235 per sq. ft.; or assuming that with headers it averaged 3 ft. thick, 10,952 cu. yd. at a cost of $2,118 per cu. yd. No proportion of cost of derrick service, plant, power, or overhead charges was distributed to cutting, but is all included in cost of quarrying. (See page 82).
At the New Croton dam, the granite facing stone was quarried at a cost (previously mentioned) of $1.80 per cu. yd. This figure included the splitting of the stones to within about 3 in. of the required dimensions. The stones were cut for a 1/2-in. joint for a depth of 4 in. from the face, and beyond this depth the joint might not exceed 2 in. in thickness. Each course was to be composed of two stretchers and one header alternately, the stretchers not less than 3 ft. nor more than 7 ft. long, nor less than 28 in. deep. The headers were to be not less than 4 ft. long, and the face work throughout was to be estimated and paid for as 30 in. thick. The cost of cutting these stones, for a rock face as described above, was $6.48 per cu. yd. The prices paid for the chief classes of labor in the quarry was as follows, for an eight-hour day: Superintendent of quarry $175 per month, superintendent of stone cutting $150 per month, foreman of stone cutters $5 per day, quarrymen $1.50 to $1.75 per day, hoisting engineers $2 per day.
The cost of quarrying and cutting granite for the Pathfinder dam, under practically the same specification as applied to the Roosevelt dam, has been stated as follows:
$0.91 per sq. ft.
Supplies, powder, etc............
0.16 per sq. ft.
$1.07 per sq. ft.
Or assuming it 3 ft. thick equals $9.63 per cu. yd. This figure does not include steel, oil, blacksmith's coal nor plant charge.
The cost of quarrying and cutting stone depends very largely upon the kind and quality of the stone; upon how it occurs in the particular quarry; whether hard or soft; whether or not it splits easily and regularly and whether it can be quarried in large well-shaped blocks with little waste. The cost of cutting further depends upon the thickness of the proposed joint. The cost at the Roosevelt dam was low because every condition was favorable. Thus the regular sheets of very distinctly stratified rock parted easily on bedding planes, the dip was one that facilitated removal from the quarry face and the stone while hard for sandstone could still be cut readily. The costs at the New Croton or Pathfinder dams would apply much more nearly to average conditions.
In the class of stone work above discussed the stones have random lengths, i.e., the length can be varied within liberal limits in order that they may be cut readily and with a minimum of waste from the stone as quarried. Specifying the exact length of the stones immediately places the work in the different and much more expensive class of dimension stone. Since the stones are quarried in a large variety of lengths, the short ones must be wasted or used for something else, while many of the remainder will be so long that considerable must be split or laboriously cut away and wasted. Again, with whatever care the limit is approached, it occasionally happens, in working a stone down to a specified dimension, that the limit is passed and the stone lost through unforeseen splitting from a single effort or step in the process of cutting.