(Science: geology) 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.
Origin: g. Grauwacke; grau gray – wacke wacke. See gray, and Wacke, and cf. Grauwacke.