but the difference is probably not so great as might at first be supposed.

In sinking large shafts the time lost in removing the drills might be lessened by working alternately on each end of the shaft, and removing the drills to the opposite end, under a shield of some kind, during the firing.

Nor is it necessary to describe here in detail the hand method of sinking, which is in every respect similar to ordinary quarry work-a gang of three men, two strikers and the drill-holder, working together.

The number of gangs employed at once is of course gov erned by the size of the shaft. In shafts of the size now or dinarily sunk, from three to five gangs work together at once, and when quick time is to be made, three shifts of eight hours each are worked per day; otherwise two shifts are worked.

The center, or that portion of the shaft immediately under the head-frame is kept in advance of other portions of the shaft to facilitate loading the bucket and to act as a sump for the collection of water.

The holes are drilled from three to six feet apart, depending upon the nature of the rock, its dip, cleavage planes, etc., and are now usually fired simultaneously in groups by an electric current.

"Rend rock" and other varieties of the higher explosives are used in hard rock, but in soft slate better results are obtained with ordinary black blasting powder.

The dip or cleavage of the rock often governs the position of the lowest point or sump, and in order to obtain the best results blasting it may sometimes be advisable to move the head-frame or to erect an auxiliary frame, in order to have the lowest point (sump) immediately beneath the sheave.

A plumb-bob is suspended from each corner of the shaft, either from the flooring or from a beam laid across the cribbing, to guide the miners in squaring the corners and sides.

After firing each blast a gang of laborers immediately descends to load the displaced rock while the miners resume drilling.

Timbering.

When the walls are self-sustaining the shaft is usually left untimbered, but sets of heavy single timbers (buntons) are placed from four to seven or eight feet (vertically) apart to divide the shaft into compartments. The cage-guides are fastened to these timbers by bolts with countersunk heads.

Under such conditions these timbers are simply fitted into notches or steps cut in the rock on each side of the shaft, and fastened tightly in place by wooden wedges.

When the sides of the shaft are not self-sustaining, complete timbering is necessary. Page plate No. 8 shows the heavy timbering and cribbing of the Hollenback shaft from a drawing by Mr. J. H. Harden. A light form of timbering for shallow shafts is shown by Page plates Nos. 6 and 7. The distance between each set of timbers is of course dependent upon the relative insecurity of the shaft walls,from four to eight feet may be taken as an average.

Various forms of joints, mortices, &c., are used, but the form is not a matter of much importance, provided the strength of the timber is not greatly impaired by the wood removed, or a tendency to split created. Wedge-shaped joints and dovetailing are therefore bad forms.

Each set of timbers is firmly wedged in place, and at the same time lined up true, by wooden wedges driven in between it and the rock wall.

When the rock is very unsafe, lagging or sheathing planks are placed behind the timbers. They are either driven in and wedged in place (lagging) or, what is better, spiked to stringers running across between each set.

At the Hollenback shaft the permanent cribbing is made of 12"X12" timbers measuring 45′ 4′′X11′ 6′′.

Outside the permanent cribbing and about one foot from it is a temporary cribbing built of 8"x10" timbers. The backing or sheathing is of 3-inch plank and a clay filling was rammed between the two cribs to exclude the surface water. The total dimensions of the earth pit to base of cribbing is 51' 2"X17' 4"x31' deep.

The plan here adopted of building a temporary crib-work as the pit is being sunk is (as has already been stated) fre