"Adit" on the other hand is an excavation that goes into a hill or mountain - in other words almost all of the underground mines that do not have shaft access are, in fact "adits"
That may be true, Ted, but the only ones I ever heard refer to "adits" were geologists and engineers.
We miners always referred to a horizontal opening into a mountain as a "tunnel". Examples: The American Tunnel and Terry Tunnel at the Sunnyside. The Treasury Tunnel at the Idarado. The Joker Tunnel at Ironton. The only true tunnel in the San Juans would have been the Meldrum Tunnel from Ironton to Pandora if it had ever been completed.
Of course things can get really interesting underground when adits become drifts or crosscuts, and shafts become winzes and raises.
Sam Bass
23 years looking at the inside of mountains