Graywacke \Gray"wacke`\, n. [G. grauwacke; grau gray + wacke
wacke. See {Gray}, and {Wacke}, and cf. {Grauwacke}.] (Geol.)
A conglomerate or grit rock, consisting of rounded pebbles
and sand firmly united together.
[1913 Webster]
Note: This term, derived 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.
[1913 Webster]