38 A NATURALIST IN THE GREAT LAKES REGION 



J_L L 



Sandstones, limy shales, limestones and coal. 



j 



I Limestone and shales. 



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



cago 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 . 



Richmond (Cincinnati) shale. 



230 ft. 



.. 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 686 ft. 



Sandstone, red marl, and shale or shaly limestones. 



FIG. 24. Diagram of strata in the Chicago region 



