Graywacke
Pronunciation : Gray"wacke`
Part of Speech : n.
Etymology : [G. grauwacke; grau gray + wacke wacke. See Gray, and Wacke, and cf. Grauwacke.] (Geol.)
Definition : Defn: A conglomerate or grit rock, consisting of rounded pebbles sand firmly united together.
Note: 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.
Source : Webster's Unabridged Dictionary, 1913