gritts, in natural history; a genus of fossils, found in minute masses, forming together a kind of powder, the several particles of which are of no determinate shape, nor have any tendency to the figure of crystal, but from rudely broken fragments of larger masses; not to be dissolved or disintegrated by water, but retaining their figure in it, and not cohering by means of it into a mass; considerably opake, and in many species fermenting with acids; often fouled with heterogeneous matters, and not unfrequently taken in the coarser stony and mineral or metallic particles.

Gritts are of various colours, as, 1. The stony and sparre gritts, of a bright or greyish white colour. 2. The red stony gritts. 3. The green stony gritts, composed of homogene sparre particles. 4. The yellow gritt, of which there is only one species. 5. The black and blackish gritts, composed of stony or talky particles.