MONOGRAPH XIX PLATE XXI 



U. S. GEOLOGICAL SURVEY 



Fig. 1.— SiderJtic chert. 



Fig, 2. — Sideritic chert, in polarized light. 



Fig, 4. — Siderit-c ..i':'l ferruginous chert. 

 THIN SECTIONS o7's,DEr',T,C ROCKS FROM THE IRON-BEARING MEMBER AND FROM LAWRENCE COUNTY, OHIO. 



Fig. 3. — Sidentic slate. 



