38 A NATURALIST IN THE GREAT LAKES REGION 



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Sandstones, limy shales, limestones and coal. 



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 



