CONTRIBUTIONS TO THE GEOLOGY OF 

 SOUTHWESTERN IOWA. 



GEORGE L. SMITH. 



During- the past summer (1917) Geologic viork has been en- 

 gaged in as opportunity offered in Montgomery, Page, and Fre- 

 mont counties. The fault line north of Thurman has been defi- 

 nitely located, on East Nishnabotna river much information of 

 importance has been obtained by observation and study of the 

 different outcrops from Essex north to Stennett, and on Noda- 

 way river at Clarinda, Shambaugh, and Braddyville outcrops 

 were visited and fossil collections made. 



The Braddyville and Shambaugh outcrops, at the present time, 

 are gTeatly obscured, and little of value can be secured at these 

 places. Search of the mine dumps at New Market and Clarinda 

 was made to secure additional material for paleontological study 

 of the shales in immediate contact with the Nodaway coal. The 

 writer is convinced the complex geology of southwestern Iowa is 

 not sufficiently knowTi or recognized at the present time. In- 

 stead of having great simplicity in its structure and stratigraphy, 

 there are numerous complications caused by erratic dips and by 

 the great Jones Point deformation, and the extent and influence 

 on the local geology of the Brownville syncline that reaches into 

 Iowa to the southeast corner of Cass county has not been ap- 

 preciated. To all this complexity is added the enormous diffi- 

 culty caused by the Pennsylvanian being deeply buried, except 

 in a few scattered localities, by Pleistocene deposits which in the 

 divides between the streams in places reach a depth of 200 feet. 

 In the valley of East Nishnabotna river as far south as Coburg 

 the Pennsylvanian is overlain unconformably by Cretaceous 

 sandstones and shales upwards of one hundred feet in thickness. 

 Exposures of strata are few in number and distant from each 

 other, which necessitates wide correlations with increased 

 chances of error. The finality in the interpretation of the geol- 

 ogy of southwestern Iowa has by no means been reached as yet. 

 In the future many attempts will be required to accurately fix 

 the stratigraphic relations of the puzzling succession of the lime- 

 stones and shales found in the Missouri stage of Iowa. Without 

 any desire to excite controversies as to what has been found in 

 other states it may be expedient for the writer to state the con- 



