• Webster's Revised Unabridged Dictionary
    • n Graywacke (Geol) A conglomerate or grit rock, consisting of rounded pebbles and sand firmly united together.☞ 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.
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Century Dictionary and Cyclopedia
    • n graywacke In geology, a compact aggregate of rounded or subangular grains of various silicious rocks, held together by a paste which is usually silicious. Graywacke is a slightly metamorphosed detrital rock, and is chiefly found in the Paleozoic series. When geology began to be studied as a science, the so-called “transition series” was frequently called the “Graywacke series,” from the predominance in it of the rock of that name. Since the establishment of the “Silurian system” by Murchison, which (in Europe at least) consists largely of rocks formerly designated as graywacke (in German grauwacke), this term has almost entirely gone out of use.
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Chambers's Twentieth Century Dictionary
    • n Graywacke grä′wak-e a kind of sandstone, consisting of rounded pebbles and sand firmly united together.
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Webster's Revised Unabridged Dictionary
G. grauwacke,; grau, gray + wacke, wacke. See Gray, and Wacke, and cf. Grauwacke
Chambers's Twentieth Century Dictionary
Ger. grauwackegrau, gray, wacke, a flint.


In literature:

Is it primitive, or is it graywacke like Catskill Mountains?
"Personal Memoirs Of A Residence Of Thirty Years With The Indian Tribes On The American Frontiers" by Henry Rowe Schoolcraft
It is a boulder of fire graywack, twelve feet long and five feet high, and faces the bed of the river.
"The Pre-Columbian Discovery of America by the Northmen" by B. F. De Costa