IOWA ACADEMY OF SCIENCES. 



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NOTES ON THE GEOLOCtY OF NORTHWESTERN IOWA. 



BY PKOF. J. E. TODD. 



I handed in the subject of this paper, intending to throw together various notes 

 which have been accumulating for several years. 



I recently took a trip to the region under consideration intending to visit several 

 localities and examine the borings of several wells, which, however. I was pre- 

 vented from doing for lack of time. Had I been able to procure careful notes 

 from all the wells I should be more decided on several points stated below. 



The following is a tabular list of the wells noted with elevations of top and 

 bottom : 



Of the Ponca well I had access to notes published by Prof. S. Aughey, who 

 visited a well when it was being bored at that place in 1880, and I also had the 

 opportunity to examine the somewhat complete core taken out by the diamond 

 drill in 1888. A summary of the result is as follows: 



Eighty feet — More or less, drift clays. 



Forty-five feet — Chalkstone capped with siliceous layers. "Inoceramus beds." 



Sixty-Sve feet — Alternate layers of fine, stratified sand and light and drab clay. 

 A pretty compact stratum of sandstone at the top, with a layer of lignite above, 

 sometimes for a little ways, 6-8 inches thick. 



Two hundred and thirty feet — Sand and sandstone. (Dakota.) 



Thirty-five feet — Sandy shale and fine light green clay with grains like "green- 

 sand." 



Fifty feet— Rusty gray, porous granular limestone above, blotched blue and 

 cream color below, dolomitic, few casts of shells resembling maci-ocheilus. 



Forty-five feet — Limestone, whitish above and capped with a layer more 

 argillaceous, containing fragments of dolomite; below blue, becoming blue car- 

 bonaceous clay. 



One hundred feet — Compact gray limestone, with portions below darker, vesicu- 

 lar in several strata. A print of a large trilobite near the top. 



Filty feet— Compact limestone with fragments of greenish Hint. 



