GEOLOGY OF SOUTHWESTERN IOWA 



The twenty feet of shale, with the associated limestone bands, 

 above the Tarkio limestone are highly fossiliferous. Two miles 

 northeast of McKissicks Grove, about one-half the distance to the 

 Mill creek outcrop, the Nyman coal has been prospected and 

 found to have a thickness of one foot. The Mill creek outcrop 

 can be correlated easily with that of McKissicks Grove. In pass- 

 ing north and east the upper limestone becomes less arenaceous 

 and more fossiliferous. 



SECTION ON MILL CREEK TWO MILES SOUTH OF RIVERTON. 



FEEX 



6. Shale, gray, weathered 10 



5. Limestone in five layers with shale part- 

 ings. The upper layer six inches 

 thick is an indurated and white lime- 

 stone composed of fragments of shells 

 and crinoid plates arranged in a hori- 

 zontal position. The two lower layers 

 ten and four inches thick are a very 

 dark gray limestone. They contain 

 numerous round lumps of calcareous 

 matter one-fourth inch in diameter. . 3 



4. Shale, calcareous, weathered yellow.... 3 



3. Shale, blue, arenaceous, contains sev- 



eral thin bands of sandstone, not well 

 exposed 9 



2. Sandstone, blue, fine-grained, micaceous, 



indurated 2 



1. Shale, blue 8 



Total 35 



On the bluff road north of Opossum creek to Thurman several 

 outcrops of the same ledge of limestone and sandstone can be 

 seen. 



COMPOSITE SECTION SOUTH OF THURMAN. 



FEET INCHES 



5. Sandstone, blue, fine texture 6 



4. Shale, gray 10 



3. Limestone, dark gray, cut by vertical 



joints into large , blocks, and con- 

 taining numerous spheroidal calcar- 

 eous lumps about one-fourth inch in 

 diameter 3 



