156 FRANCIS M. VAN TUYL 



POST-PENNSYLVANIAN HISTORY OF THE BASIN 



Subsequent to the deposition of the Paleozoic the Mississippi 

 Valley region was uplifted. It seems probable that the geosyncline 

 was deepened somewhat at this time and that secondary folds were 

 developed. But the fact that the regularity of the basin has not 

 been appreciably interfered with indicates that this secondary 

 folding was not of great importance. Following this uplift the 

 region underwent peneplanation. That the deposits occupying the 

 geosyncline were peneplained by the beginning of the Upper Creta- 

 ceous is shown by the fact that the basal deposits of this age rest 

 upon the beveled edges of the dipping formations, ranging in age 

 from the Lower Mississippian on the marign of the basin in Iowa 

 to the Permian in Kansas, at approximately the same elevation 

 everywhere . 



There is no evidence of further movement of the geosyncline 

 during or since the Cretaceous apart from the regional uplift 

 which brought the area to its present level. The present course of 

 the Missouri River across the basin was obviously taken some time 

 after the development of the peneplain. 



