Adit - A nearly horizontal passage from the surface by which a mine is entered and dewatered. A blind horizontal
opening into a mountain, with only one entrance.
an adit is an entrance to an underground mine which is horizontal or nearly horizontal, by which the mine can be entered, drained of water and ventilated.
Adits are driven into the side of a hill or mountain, and are often used when an ore body is located inside the mountain but above the adjacent valley floor or coastal plain. In cases where the mineral vein outcrops at the surface, the adit may follow the lode or vein until it is worked out, in this case the adit is rarely straight. The use of adits for the extraction of ore is generally called drift mining.
Adits can only be driven into a mine where the local topography permits. There will be no opportunity to drive an adit to a mine situated on a large flat plain, for instance. Also if the ground is weak, the cost of shoring up a long adit may outweigh its possible advantages.