The following summary description of slope-sinking and timbering will, therefore, be understood to apply as well to planes. The method of sinking rock-slopes is of course somewhat different.

When the location of a projected slope has been determined, the first procedure is the erection of a temporary sinking plant. This usually consists of an old engine and drum placed upon a temporary timber foundation or a rude crib-work loaded with stones. A rough frame house is erected over the engine, and one or two tubular boilers or two to four plain cylinder boilers supply the steam.

For a short distance-varying with the nature of the ground but usually ranging from twelve to eighteen feet in depth-the sinking is carried down as an open cut and the earth and rock are thrown out by hand.

As soon as the roof becomes sufficiently strong the miners begin to work in under it, and the work of timbering is commenced. At the same time a single or double track is carried down and the coal and other material is raised in a car or self-dumping skip.

When a skip is used, the track is continued up on a trestle some distance above the mouth of the shaft, and a headsheave placed in proper position to draw the skip up the required distance to dump the material into a dump-car or pocket beneath the trestling.

The width of the sinking depends upon the width of the cars and the number of compartments necessary. A common arrangement is to divide the opening into three compartments, two of large size for raising coal and a third of somewhat smaller size for the pump rod, column-pipe, and for use as a traveling-way and this is also used as an air-way during the sinking.

The practice sometimes adopted of having but one hoisting compartment laid with three rails with a turn-out at the middle of the hoist, while cheaper at first, is of doubtful economy, as rope breakage on one side or falling coal from the upper wagon, is likely to demolish the other, and on planes and slopes so constructed. collisions at the turn-out

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are not infrequent. The same objections apply to slopes with a single track and a passing turn-out at the middle.

It will hardly be necessary to refer here to slopes with a single track throughout. They are used only when the output is small. Slopes designed for three compartments as above described are usually driven from sixteen to twenty-two feet wide.

When the dip does not exceed thirty-five or forty degrees, the height of the slope is made about the same as that of the gangways, usually about seven feet in the clear from the top of the rail to the under side of the collars, measured not in a vertical line, but at right angles to the dip. On steeper dips the prevalent custom of raising the cars on slope cages (to prevent spilling the coal) necessitates a much greater height; but when the car is raised in gunboats, the ordinary height suffices.

*

In slope sinking the operation of getting out the coal is similar to gangway driving, and is done with similar tools; but when in order to straighten the slope, or for other reasons, the driving is done in rock, rock drilling tools and explosives are used.

The bottom of the slope is kept in advance of the top or vice versa by putting in holes nearly vertical or inclined slightly down the pitch, and one corner is kept in advance of the main face to collect the water and give a loose end in blasting.

After the bottom has been underholed by a series of shots, the top is blown down as in gangway work; but this is not the universal practice, as the top is sometimes kept in advance of the bottom, and the lower benches blown up afterwards.

The timbering and track laying are carried down pari passu with the sinking, and kept within a few feet of the working face.

Slope timbering.

This is similar in many respects to gangway timbering, but the joints are cut with more care, and square timber is

* Monitors or skips.

used much more largely for slopes than for gangways. It also often differs from gangway timbering in many other particulars, as shown by Page-plate No. 10, and by Figs. 10 to 15.

The above illustration (Fig. 10) shows a slope with no other timbering but a center-prop. On steep dips a heavy foot-sill is let into the rib on each side to prevent the road bed from slipping down the pitch.

When complete timbering is necessary, the form shown by Fig. 11 is frequently used. The legs and collars and center-prop are similar in every respect to heavy double track gangway timbering, and they are surrounded by lagging similarly placed. (The timbers are too massive in Fig. 11.)