BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



VOL. 27, PP. 305-324, PLS. 15-17 JUNE 3, 1916 



PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



ALEXANDRIAN KOCKS OF NORTHEASTERN ILLINOIS AND 

 EASTERN WISCONSIN 1 



BY T. E. SAVAGE 



(Presented before the Paleontological Society December 30, 191J/.) 



CONTENTS 



Page 



Introduction 305 



Alexandrian rocks and sections of northeastern Illinois 305 



Alexandrian strata in Wisconsin 308 



General statement 308 



Description of sections 308 



Correlation of the Mayville beds of Wisconsin with the Alexandrian rocks 



of northeastern Illinois 310 



Correlation of the Alexandrian rocks of the Mississippi Valley with the 



early Silurian strata of Anticosti 312 



Relation of the Sexton Creek limestone to the Cataract formation 313 



History of the Alexandrian epoch in the Mississippi Valley 314 



Description of species 316 



Explanation of plates 323 



Introduction 



The Silurian rocks of northeastern Illinois and eastern Wisconsin occur 

 over a belt 350 miles long and from 20 or less to 50 miles wide, extending 

 from below Kankakee, Illinois, northward to the extremity of Green Bay 

 Peninsula, in Wisconsin. This area is on the east side of the La Salle 

 anticline and the highland of central Wisconsin, away from which the 

 strata dip gently toward the east; so that the older Silurian rocks reach 

 the surface at intervals only along the west border. 



Alexandrian Rocks and Sections of northeastern Tllinots 



The most southern exposure of Alexandrian rocks in this region is in 

 the banks of Horse Creek, iy 2 miles east of the town of Essex and about 



1 Manuscript received by the Secretary of the Geological Society November 27, 1915, 



(305) 



