U. S. GEOLOGICAL SURVEV 



MONOGRAPH XIX PLATE XVIII 



Fig, 1— Graywacke-slate. 



Fig. 2.— Grayvvacke-sfate m polarized light. 



Fig. 3.— Cherty slate. F,g 4.-Sericitic and chloritic slate. 



THIN SECTIONS FROM THE QUARTZ-SLATE MEMBER. 



