SMITHSONIAN EXPLORATIONS, I927 



31 



Fig. 31. — Limestone Mountain, near Baraga, Mich. This isolated erosional 

 remnant is the only tangible proof that parts of the northern peninsula of 

 Michigan were basins of marine deposition during most of Paleozoic time. 

 (Photograph by E. R. Pohl.) 



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FiG. 3J. — A quarry face illustrating one of the most interesting features 

 of stratigraphy. The black line through the center of the picture draws the 

 boundaries of two formations and shows surface erosion of the one and 

 overlap bv the other. Such a contact is called an unconformity. Near 

 Petoskey, 'Mich. (Photograph by E. R. Pohl.) 



