THE SILURIAN PERIOD 



105 



Guelph dolomitic limestones. The Clinton formation rests con- 

 formably upon the Medina beds, but is more widespread than they. 



Fig. 59 

 Map showing the surface distribution (areas of outcrops) of Silurian strata in 

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

 Survey.) 



It extends through the Appalachian Mountains, westward from 

 central New York to Lake Huron and Indiana into Wisconsin, 

 and probably through Illinois and Missouri. It is also known in 



