AGE OF GYPSUM OF CENTRAL IOWA 729 



dence seems sufficient to show that a deposit so extensive and 

 so pure could not have been formed in a basin without oceanic 

 connection, and an oceanic connection during the Eocene for a 

 basin in central Iowa seems impossible. 



Attention has lately been called to a well boring at Cherokee 

 which reached a depth of 800 feet. At the bottom, beneath a 

 sandstone that was certainly Dakota, and at a depth below any 

 possible Cretaceous beds in this state, sixteen feet of gypsum 

 are said to have been found. The persons making the report 

 are regarded as reliable. Gypsum is readily identified and the 

 report has significance. An effort is being made to determine 

 positively the nature of the material regarded as gypsum. If 

 the report is correct it has a direct bearing on the question in 

 hand, for the position of this gypsum would indicate that it 

 belonged to the close of the Carboniferous. 



The claims of the Cretaceous have been pressed also, on other 

 than stratigraphic grounds.^ Reference to the geological map of 

 Iowa shows that Cretaceous deposits are present throughout the 

 greater part of northwestern Iowa, and that they approach within 

 thirty miles of Webster county, at Auburn in Sac county, where 

 they appear as chalk. The Cretaceous in Iowa consists of sand- 

 stone of the Dakota stage, and shales, limestone and chalk of 

 the Colorado stage. Sandstone, shales, and limestone have yielded 

 abundant fossils which definitely fix their age. Other things 

 being equal, it would be somewhat more natural to regard the 

 Webster county gypsum series as an outlier of the Cretaceous 

 than of the Permian which is farther away, yet the distance is 

 not so great as to render a correlation with the Permian in any 

 degree improbable, if the preponderance of other evidence favors 

 such a view. A review of Cretaceous climatic conditions is first 

 of all necessary, for if aridity is a more striking characteristic of 

 the Permian than of the Cretaceous, the Cretaceous age of the 

 gypsum can hardly be established. The Dakota sandstone is at 

 times red, but this color does not everywhere prevail, and it does 

 not characterize the Cretaceous shales and limestones in any 

 degee. The Dakota sandstone abounds in fossils, as does the 



^lowa Geological Survey, Vol. Ill, p. 290. 



