graywacke Meaning, Definition & Usage

Gray"wacke` noun
Etymology
G. grauwacke; grau gray + wacke wacke. See Gray, and Wacke, and cf. Grauwacke.
Definitions
  1. (Geol.) A conglomerate or grit rock, consisting of rounded pebbles sand firmly united together. ✍ This term, derved from the grauwacke of German miners, was formerly applied in geology to different grits and slates of the Silurian series; but it is now seldom used.

Webster 1913