BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 5, pp. 231-242 February 27, 1894 



CRUSTAL ADJUSTMENT IX THE UPPER MISSISSIPPI VALLEY 



BY CHARLES ROLLIN KEYES 



(Presented before the Society December 29, 1893^ 

 CONTENTS 



Page 



Introductory 231 



Carboniferous Basin of the Mississippi Valley 232 



Extent 232 



Structure 233 



Geologic Provinces •. 233 



Character of Deformations 233 



Folds 234 



Principal Features 234 



Minor Corrugations 235 



Faults 235 



Alleged Faulting 235 



Dislocations in Iowa 2o6 



Normal Faults 236 



Step Faults 237 



Trough Faults 238 



Clay Seams 239 



Origin of the Faults 240 



241 

 Summary 



Introductory. 



The effects of orogenic moveixients so obvious everywhere in all moun- 

 tainous regions rapidly lose their more salient characteristics as the dis- 

 tance increases from the heart of the system to the more level, plain-like 

 districts above which they rise. In the lowland ])lains, such as exist in 

 the Mississipiji basin, the corrading power of running water is reduced to 

 a minimum, and profound secular decay or heavy glacial accumulations 

 obscure almost completely everything except the most prominent struc- 

 tural features. Indications of low folds or shallow synclines are often 

 visible in this region, but dislocations of strata are rarely found. That 

 the latter are much more frequent than is perhaps generally supposed, 



XXXTI-Bur.L. GEor.. Soc. Am., Vol. 5, 1893. V-<jl) 



