GEOLOGY OF SOUTHWESTERN IOWA. 357 



By referring to the descriptions of Ringgold, Union, Adair, 

 and other counties to the eastward, it will be seen that the 

 Drift Deposit there is stated to be very deep. Going westward 

 from that region, we find the drift gradually diminishing in 

 thickness until we reach the counties that border upon the 

 Missouri river, where it is sometimes found not exceeding 

 half a dozen feet in thickness between the stratified rocks 

 beneath it, and the Bluff Deposit above it. The Bluff Deposit 

 is so deep throughout Fremont county, and the drift so thin, 

 it is only at a few points where the latter has been bared by 

 the erosion of the valleys that it is seen at all. Thus, only 

 the immediate beds of the larger streams contain any 

 sand or gravel, while the banks of all of them, and the beds 

 also of the smaller branches and creeks, are composed of 

 the fine material of the Bluff Deposit, and are usually soft 

 and muddy. 



Geology. The strata only of the Upper coal-measures have 

 been found exposed in Fremont county, and in consequence of 

 the great thickness of the Bluff Deposit, the exposures of these 

 are very few. None have been found in the valleys of either 

 the Mshnabotany's, and, with the exception of a slight one 

 in the valley of Walnut creek, the only exposures are to be 

 found at distant intervals along the base of the bluffs that 

 border the Missouri river flood-plain. They usually extend 

 only a few feet in height above the level of the plain, and are 

 then lost from sight beneath the Bluff Deposit, or the slight 

 intervening accumulation of drift, but in the northwestern 

 part of the county a few exposures reach considerable height 

 above the general level of the flood-plain. 



On land of Mr. John Wilson, section 23, township 70, range 

 43, there are some fine exposures of Upper coal-measure 

 strata, which reach the greatest aggregate thickness of any 

 yet known within the State, westward from Madison county. 

 It is therefore a locality of great interest and importance in 

 the study of that formation in southwestern Iowa. The strata 

 observed there are represented by Fig. 35, and by the section 

 following it. 



