U. S. GEOLOGICAL SURVEY 



MONOCRAPH XIX PLATE XXXII 



Fig. 1 —Micaceous graywacke. 



Fig. 2. — Biotitic and muscovitic graywacke. 



Fig. 3,— Biotitic gfaywacke. Fig. 4.— Biotitic and chloritic graywacke. 



THIN SECTIONS OF GRAYWACKES FROM THE UPPER SLATE MEMBER, 



