728 FRA NK A . WILDER 



with red shales occurring in both Europe and America, and the 

 striking resemblance which the series bears to the Permian only 

 300 miles to the west — carry great weight. The Iowa series 

 might reasonably be interpreted as an outlier of the Permian of 

 Kansas and Indian Territory. During the long interval between 

 its deposition and that of the drift which now protects it erosion 

 had an abundant opportunity to remove the Permian from the 

 intervening territory. The gypsum was doubtless protected by 

 heavy beds of the red shales, for, had it been exposed long, it 

 must have yielded to the solvent and erosive action of water. 



The gypsum has been referred to the Cretaceous and to the 

 Eocene for stratigraphic reasons. In the region of the Missis- 

 sippi valley and great plains there are two well-marked uncon- 

 formities to be considered. One occurs at the base of the 

 Cretaceous, and the other at the base of the Eocene. By an 

 unconformity also, the gypsum beds of Iowa are separated from 

 the Coal Measures. The Missourian, which farther west attains 

 a considerable thickness, is here wholly absent, and instead of 

 deposition, erosion was probably taking place in the Fort Dodge 

 region during this stage. No unconformity has been recognized 

 between the Permian and the Coal Measures in Texas and 

 Kansas. The absence of an unconformity in these regions does 

 not preclude the possibility of a local unconformity in Iowa, 

 More striking unconformities, local in nature, between certain of 

 the older formations in the state, can be positively demonstrated. 

 The surface beneath the gypsum was plainly not brought down 

 to a base level before the deposition of the gypsum, for the 

 gypsum lies in an erosion trough which has rather steep slopes. 



In view of the important climatic conditions which will be 

 presently considered, which seem to have been particularly 

 favorable during the Permian all over the world, a local uncon- 

 formity may be admitted if it obviates the necessity of referring 

 the gypsum to the Cretaceous, where these conditions were 

 notably absent. 



To regard the gypsum as belonging to the Eocene seems 

 impossible, when the conditions under which it was formed, con- 

 sidered in a later paragraph, are taken into account. The evi- 



