38 



A NATURALIST IN THE GREAT LAKES REGION 



>■ Sandstones, limy shales, limestones and coal. 



< 

 I— I 



u 



l-H 

 > 



o 

 p 

 pj 

 o 



< 



\ II I -r-r 



,1 .1 , 1 



I I I ~7'n' 





Limestone and shales. 



■* Below this level are the rock strata of the Chicago area as revealed 

 in a well bored at Lockport (after Alden, U.S. Geological Survey). 

 Above strata found to south and east; the Devonian is slightly 

 represented at Chicago. 



> Niagaran, dolomitic limestone 230 ft. 



Richmond (Cincinnati) shale no ft. 



> Galena-Platteville (Trenton) limestone 300 ft. 



> St. Peter sandstone . 210 ft. 



> Lower Magnesian formation 395 ft. 



Dolomitic limestone, red marl, and shale, or shaly limestones. 



> Potsdam formation 



Sandstone, red marl, and shale or shaly limestones. 



686 ft. 



Fig. 24.— Diagram of strata in the Chicago region 



