These two mountains are underlain primarily with late Cretaceous dark greenish-gray graywacke, a poorly sorted sandstone containing angular rock fragments, about ten percent feldspar and detrital chert.
12.
The summit area of Mount Diablo is made up of deposits of gray sandstone ( graywacke ), chert, oceanic volcanic basalts ( greenstone ) and a minor amount of shale.
13.
These metamorphic rocks appear to be the result of the metamorphism of Middle to Early Cambrian deep sea flysch composed of interbedded, mudstone, shale, clayey sandstone, calcareous sandstone, graywacke, and sandy limestone.
14.
A particularly troubling paradox was the occurrence of blueschist blocks ( low temperature and high pressure metamorphic rocks ) in direct contact with graywacke ( a coarse sandstone with lithic fragments ) that was deposited in a sedimentary environment.
15.
To the Lane Construction Co ., which has owned Snake Mountain for 50 years, it is a valuable hunk of Rensselaer graywacke and Metawee argillite, just the right kind of rock for blending with asphalt or cement.
16.
It is 21 paces in diameter at the base, in diameter at the top and high; largely composed of boulders and one large boulder of graywacke stone, long, is partially buried on the top edge facing south.
