74 



GEOLOGICAL FORMATIONS. 



founded it with a lithologically similar sandrock situated at the 

 base of the Coal Measures, and consequently the latter is 

 located upon, instead of beneath, the Kaskaskia. For con- 

 venience in reference, and in order to avoid further confusion, 

 this arenaceous bed will be called the Aux Vases sandstone, 

 from the river of that name in Ste. Genevieve county, where 

 the rock is well exposed. In northern Missouri and Iowa, where 

 the superior member of the Mississippian series is wanting, 

 the basal sandrock of the Coal Measures occupies apparently 

 the same stiatigraphical position as the. lower Kaskaskia 

 sandstone: that is, directly superimposed upon the Saint Louis 

 limestone. 



KaskasTiia Limestone, — The main body of the formation 

 is composed of heavily bedded limestones below, and of plas- 



Fig. 6. Sandstone in Gorge of Kaskaskia Beds. Chester. 



tic clay-shales with thin calcareous bands above. Every- 

 where over those portions of the upper Mississippi valley in 

 which the Kaskaskia is absent, the Saint Louis rocks, as already 

 stated, are weathered and deeply channeled, many gorges pass- 

 ing downward even into the Keokuk, thus showing pretty con- 

 clusively that these portions of the territory were actually 

 above sea level during a part of the Kaskaskia deposition. 

 That the northern shore line continued to move "southward 

 after the Kaskaskia epoch had begun, and perhaps even until 

 the latter half of the interval had set in, is shown by the sue- 



