72 



GEOLOGICAL FORMATIONS 



boring states has been claimed by White*, but the recent 

 evidence bearing upon the point is not near so conclusive as 

 would be desired. The differences in thickness of the limestone 

 have been alluded to already. This is due partly to the thinning 

 out of the strata northward, and partly to the subaerial erosion 

 prior to the deposition of the Coal Measures of the region. 



Over all the northern area of the Saint Louis a character- 

 istic brecciated rock is observable. But south of the Missouri 

 river evenly bedded limestones are present, with occasional 

 extensive beds of oolite. In places, as at Ste. Genevieve, 

 the oolitic limestones present perfect cross-bedding, such as is 



Sc-ale. Y 



Fig. i. Cro8s-l)edding of Oolite. 



commonly seen in sandstones — a fact which is very suggestive 

 in its bearing upon the origin of certain rocks of this kind. 



The faunal features of the Saint Louis are peculiar in 

 many respects, and quite distinct from those of both the over- 

 lying and underlying strata, particularly from the latter. 



KASKASKIA, OE "CHESTER," BEDS. 



Aux Vases Sandstone. — In southern Illinois and southeast- 

 ern Missouri, the Kaskaskia comprises extensive beds of lime- 

 stone and shale. Everywhere over this district the calcareous 

 portions, which greatly predominate in the lower part of the 



*Geology of Iowa, Vol. I, pp. 225-229. 1870. 



