The Story of Slate - 1923 - Page 5
A channeler is a machine operated by steam or compressed air that chops the rock by repeated blows of heavy chisel-like bars.
In this way a vertical channel or groove 2 or 3 inches wide and possibly 12 feet deep is cut along the wall of the quarry, and cross channels subdivide the rock into large rectangular masses.
The latter are broken free from the quarry floor by driving wedges in drill holes or by the discharge of a small amount of black blasting powder.
The large masses are subdivided by splitting along the direction of slaty cleavage and by making fractures in other directions with wedges driven into drill holes.
Masses of slate thus obtained weighing 1 to 3 tons are hoisted to the surface.
Great chains are placed about them and they are elevated with steel cables wound on drums by powerful hoist engines.
Some slate quarries have been worked for many years and thus are of wide extent and very deep.
Several of the Pennsylvania quarries are more than 400 feet in depth.
The treatment that a block of slate receives after it is removed from the quarry depends entirely on the purpose for which it is to be used.
If it is to be converted into roofing slates the process is very simple.
The block is first subdivided into masses 24 to 30 inches in length and the thickness of 8 slates.
This is the task of the block-maker.
The splitter then takes these masses and with a thin flexible steel chisel and a wooden mallet he subdivides each block, always splitting it in the center, until the 8 slates are obtained.
The trimmer then places them on a trimming machine where the irregular edges are cut away leaving the largest perfect rectangle of a given standard size that the slab will make.
Trimming is done with a heavy blade like a great meat cleaver, operated with a foot treadle, or sometimes with a curved rotating blade like that of a lawn mower.