Webster's Revised Unabridged Dictionary · 1913

Outcrop

Outcrop , noun

(a)
(Geology) The coming out of a stratum to the surface of the ground.
(b)
(Geology) That part of inclined strata which appears at the surface; basset. — Lyell

Outcrop , intransitive verb

(Geology) To come out to the surface of the ground; -- said of strata.