U. S. GEOLOGICAL SURVEY 



MONOGRAPH XIX PLATE XX 



Fig. 1.— Quarlzite. 



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 Fig. 2. — Quaitzite, in polarized light. 



Fig, 3. —Ferruginous c|uanzite, Fig. 4,-Fefrugir,ous quartzite, in polarized light. 



THIN SECTIONS FROM THE UPPER HORIZON OF THE QUARTZ-SLATE MEMBER, 



