Conglomerate:
cemented river gravel from Orinda Formation
This rock is displayed in
“Sibley's Geological
Treasures” collection on the roofed patio of the visitor
center in the Robert Sibley Volcanic Regional
Preserve. The above caption is the same that is given on-site
(June 11, 2012).
Conglomerate is a sedimentary rock composed of
water-worn rock or
pebbles that are held within a
finer-grained matrix of siliceous (silica-containing or
silica-resembling) or argillaceous (clayey) substances.
In contrast to breccias, which contain angular fragments in their
matrix, conglomerates consist of matrix-embedded
rounded fragments.
