COAL-CUTTING MACHINERY
When excavating coal the heading is first undercut, that is, a deep slot is cut in the wall of coal along the floor line. Then blast holes are bored into the coal above this cut so that when the charges are fired the coal will be broken downward. To undercut the coal special machines are used, driven by compressed air or electricity. These have endless chains fitted with chisel or pick points that bite into and cut the coal. After the material has been shattered and reduced to fragments of convenient size special machinery may be employed to shovel it away from the heading and into dump cars. One electrically driven shoveling machine which was tried out on some of the Catskill aqueduct excavation had a broad open shovel which could be driven into the pile of rock fragments under the control of an operator and would scoop up the material, delivering it upon a traveling belt conveyor which carried it on to the train cars. Many types of mechanical shoveling and loading machines have been built for use in mines. They are driven either by pneumatic or electric power.