SHAFT SINKING

is empioyed in mining for working mineral deposits which cannot be reached by tunneling. Shafts are generally cylindrical or rectangular in cro section, and are lined with steel, concrete, masonry, or timber, They may be either vertical or inclined, the latter invariably rectants Rectangular shafts may. be vided into four or more com ents, but cylindrical shafts rarely have more than two. The sinking of a shaft in dry rock is not difficult, but where the ground is soft and wet the proce is troublesome and expensive. Vertical shafts may be 5000 feet in depth, and inclined shafts are sometimes more than 6,000 feet long. Shafts are used for hoisting and ventilating purposes, and or pumping and transmitting underground steam or other power.