TOAD-STONE, noun [toad and stone.] In mineralogy, a sort of trap rock, of a brownish gray color. The toad-stone of Derbyshire is generally a dark brown basaltic amygdaloid, composed of basalt and green earth, and containing oblong cavities filled with calcarious spar.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI