THE WESTERN INTERIOR GEOSYNCLINE 151 



been brought about in part by subsidence during the post-Cherokee 

 stages of the Pennsylvanian and in part by post-Pennsylvanian 

 deformation. The data are not sufficient at present to warrant an 

 estimate of the relative importance of each of the two. There is 

 evidence that the original outlines and relations of the basin have 

 been considerably modified by these later readjustments. 



The magnitude and significance of the basin have been demon- 

 strated by the construction of 100-foot contours on the base of the 

 Coal Measures, from data furnished by the reports of the state geo- 

 logical surveys of Iowa, Missouri, and Kansas (Fig. 1). Contours 

 showing the altitude of the base of the Coal Measures in Missouri 

 have already been drawn by Hinds and Greene, 1 and these have been 

 copied directly. Norton has also drawn a similar contour map for 

 the southwestern and south-central portions of Iowa, 2 and this has 

 been adopted with little modification. 



The presence of this basin not only explains the great dis- 

 similarity between the Coal Measures of this field and those of the 

 eastern interior field, which were undoubtedly deposited in a dis- 

 tinct basin, but also explains the belted arrangement of the out- 

 crops of the Pennsylvanian formations in Iowa, Missouri, and 

 Kansas, where the younger members are approximately confined 

 to the center of the basin, progressively older ones being exposed 

 toward its margins. 



There can be no doubt that this geosyncline exerted an impor- 

 tant influence on sedimentation in this region during the Pennsyl- 

 vanian. The work of Hinds and Greene in Missouri has furnished 

 valuable data bearing on this point. Referring to the Cherokee 

 deposits of that state they say : 



The Cherokee sea, advancing from the west or southwest, first invaded 

 Missouri in the vicinity of Forest City, Holt County, and soon extended north- 

 east as a long shallow arm through Worth, Harrison, and Mercer counties into 

 Iowa. When about 150 feet of Cherokee sediments had been laid down the 

 arm had broadened out to the southeast so as to embrace Buchanan and Platte 

 counties, and a short time later Clay, Jackson, and Livingston counties. After 

 the deposition of nearly 400 feet of material in the Forest City area the sea 

 covered practically all of the western tier of counties, except Atchison, and 



1 Mo. Bur. Geol. and Mines, Vol. XIII, 2d Ser. (1915), PI. 25. 

 2 Iowa Geol. Survey, XXI (1912), 1101. 



