The erection of the necessary machinery on the surface, and the opening of the mine.

The boring of the pits to the lowest part of the water-bearing strata.

The placing of the tubbing.

The introduction of cement behind the tubbing to complete its solidity.

The extraction of the water from the pits, and the placing of the wedging cribs, or "faux cuvelage," below the moss box. Figs. 119 to 121 show in elevations and in plan the plant usually employed on the sur

face. O is a small capstan engine, having a cylinder 20 inches in diameter and a stroke of 32 inches, working on the third motion. tached to this engine, and working in the small pit C, is a counterbalance weight.

Fig. 119.

This engine is used for raising and lowering boring tools, and for lifting the débris resulting from the boring. As far as the platform, which is about 10 feet from the surface, the pit has a diameter of 19 feet, or 4 feet more than the diameter of the pit below. A at level of about 38 feet above this platform there is

a tramway on which small trucks run, carrying the debris cylinder on one side, and the boring tools on the other. At a level of 48 feet above the platform are placed supports for the wooden spears to which the boring tools are attached. The machinery for boring is worked by a cylinder, which has a diameter of 39 inches, and a full stroke of 39 inches, the usual

Fig. 120.

stroke varying from 2 feet to 3 feet. A massive beam of wood transmits motion from this cylinder to the boring apparatus, the connection between the beam and the piston-rod and the beam and the boring tools being made by a chain. The engine-man sits close to the engine, and applies the steam above the piston only. The down stroke of the boring tools is caused by the sudden opening of the exhaust, and a frame then prevents the shock of the boring rods from being too severe. The engines work at speeds varying from 12 to 18 strokes a minute, according to the character of the strata passed through.

After the working platform is fixed, the first boring tool applied is the small trepan, Figs. 122 to 125. This tool is attached to the wooden beam by the same arrangement shown by Fig. 109. The boring tools can be lowered at pleasure by means of an adjusting screw. Next in order comes the handle for boring. This is worked by four men on the platform, and and is

turned by the aid of a swivel. Attached to the handle-piece are wooden rods, made from Riga pitch pine. These rods are 59 feet in length and 72 inches

square. A swivelled

Fig. 121.

ring, Figs. 126, 127, is attached to the rope when raising and lowering the boring rods. The small trepan cuts a hole 4 feet 8 inches in diameter, and has fourteen teeth, fitted in cylindrical holes and secured by pins entering through circular slots. The teeth are steeled. At a distance of 4 feet 4 inches above the main teeth of the trepan there is an arm, with a tooth at each end. This piece answers the purpose of a guide, and at the same time removes irregularities from the sides of the hole. At a distance of 13 feet 6 inches above the main teeth are the actual guides, consisting of two strong arms of iron fixed on the tool, and placed at right angles to each other. The hole made by the small trepan is not kept at any fixed distance in advance of the full-sized pit, but the distance generally varies from 10 to 30 yards. With the small trepan, which weighs 8 tons, the progress varies from 6 to 10 feet a day.

Fig. 124.

B

Plan of Guide B.

Fig. 125.*

The large trepan, Figs. 128 to 130, weighs 16 tons, is forged in one solid piece, and has twenty-eight teeth. A projection of iron forms the centre of this trepan, and fits loosely into the hole made by the small trepan, acting as a guide for the tool. At a distance of 7 feet 6 inches above the teeth, a guide is sometimes fixed on the frame, but is not furnished with teeth. At a distance of 13 feet

E

Fig. 122.

Fig. 123.

Fig. 126.

Fig. 127.