Referring to material that is formed or introduced from somewhere other than the place it is presently found: Allochthonous rocks are those whose primary constituents have not been formed in their natural or original places.

Allocthonous is the misspelling of allochthonous.

A type of coal arising from accumulations of plant debris moved from their place of growth and deposited elsewhere: In her book on geology, Jill learned that allochthonous coal originated from a mass of plant remains transported from the place where they grew to somewhere else.