GEOLOGY OF SOUTHWESTERN IOWA 



FEET INCHES 



12. Light shale 3 



11. Black shale 2 8 



10. Gray limestone, impure, shaly 3 4 



9. Gray shale 8 



8. Limestone, impure, shaly 2 



7. Green shale 16 9 



6. Gray shale 37 3 



5. Gray limestone 1 2 



4. Gray shale 44 3 



3. Caprock limestone 4 10 



2. Black shale 4 



1. Coal, Nodaway 1 6 



Total 212 7 



Records obtained of two core drill holes and two coal mine 

 shafts within one mile of Coin show no constant horizon that can 

 be correlated above the Nodaway coal in the City Bluffs shale. 



Eecent grading at Hamburg on the street north of the school 

 house has exposed an excellent section. The bluff at this place 

 reaches a height of about one hundred and fifty feet above the 

 river flood lands, with the slope of the west face reaching nearly 

 45 degrees. The east slope is somewhat less. The crest is wide 

 enough only for a narrow footpath. The surface of the shale 

 bed rock closely follows the contour of the bluff, and at the con- 

 tact of the shale and loess composing the upper part of the bluff, 

 does not show any traces of weathering previous to the deposition 

 of the loess. 



The Iowa Geological Survey has published several sections of 

 the strata in this bluff, only one of which is correct, that of J. A. 

 Udden, in Vol. XIII, Iowa Geological Survey. At the time of 

 the visit of Dr. Calvin and the writer the limestone and lower 

 sandstone layers were concealed by debris and were not seen. 



SECTION AT HAMBURG BLUFF. 



FEET INCHES 



6. Sandstone, yellow, coarse grained, the 

 grains composed of subangular frag- 

 ments of quartz 3 



5. Shale, blue, weathered gray, contains 



concretions of pyrite 15 



4. Limestone, dark gray, arenaceous, cut 

 by vertical joints, brecciated, occasion- 

 ally contains spheroidal lumps of dark 



