338 COUNTY AND REGIONAL GEOLOGY. 



the case, the extreme border of the Mshnabotany sandstone 

 may intervene in some parts. 



The most northerly point in Middle river valley, at which 

 an exposure of strata occnrs, is near the right bank of the 

 river, about three miles southward from the north boundary 

 of the county. Below this, to the point where the river 

 enters Madison county, similar strata are exposed in the 

 banks of the stream at rather rare but gradually increasing 

 intervals, until, near the eastern border of the county, the 

 exposures are somewhat numerous. All these exposures are 

 referred to the lower half of the series of limestone strata 

 shown in the Winterset section. It will be remembered, also, 

 that all the strata exposed in the valley of Grand river, in 

 Union and Decatur counties are referred to the same horizon. 

 It is believed, also, that all the strata exposed in the counties 

 of Adair, Union, and Decatur, belong within a verticle range 

 of less than one hundred feet. Nearly all the strata exposed 

 along the valley of Middle river are limestone. They usually 

 amount to only a few feet in vertical thickness, but one of 

 them, on section 12, township 76, range 31, presents a vertical 

 F IG . 26. thickness of about twenty feet 



e to^ mm # of limestone. More argil] a- 



& ceous strata exist beneath these, 

 and are exposed in the banks 

 of Drake's creek, on section 13, 

 township 75, range 30. These 

 ^^z^vp^^Jl^g? I" are shown in the following 

 y^ ^fs^^ ]^s^^M^= \ section and illustrated by Fig. 



Section at Drakes Creek. 



No. 6. Black, carbonaceous shale, a few inches at top consisting of 

 impure coal 



No. 5. Marly Clay 



No. 4 Hard, bluish, impure limestone 



No. 3. Brownish, clayey shale 



No. 2. Hard, dark colored, impure limestone 



No. 1. Fine grained, micaceous sandy shale, becoming darker and 

 more clayey at top 



Total 



6" 



2 



feet. 



Y % foot. 



1 



foot. 



1 



foot. 



K 



foot. 



22 



feet. 



