THE DEVONIAN PERIOD 



123 



shales and limestones, has very much the same distribution as the 

 Onondaga, except for the absence of Erian from the south end of 



Fig. 68 

 Map showing surface distribution (areas of outcrops) of Devonian strata in 

 North America. (Modified by W. J. M. after Willis, U. S. Geological 

 Survey.) 



Hudson Bay, and additional Erian areas in the middle Appala- 

 chians, Iowa, northern Missouri, and just west of Lake Winnipeg. 

 In the east, shales were deposited, attaining a thickness of 1500 



