U. S. OEOLOOICAL SURVEY 



MONOOOAPH XXVIir Pl_ III 



Potsdam or St Marys Sandstone 



FiG. 1.— PORTION OF BROOKS'S MAP OF THE UPPER PENINSULA OF MICHIGAN. 



1^ 



Iron-bearing serie 



<;s 



Peridotite 

 Fig. 2. — IRVING'S OUTLINE MAP OF THE MARQUETTE D'STRICT, 



Lake Superior sandstone 



