86 aEOLOGICAL FORMATIONS. 



other successively, and that should the strata of the upper 

 Coal Measures in the northwestern part of the state be pene- 

 trated by a shaft, the raembers of the middle and lower Coal 

 Measures would be successively encountered. The reservation 

 is generally made, however, that some of the beds will proba- 

 bly thin out, disappear, or be replaced by others, so that ex- 

 actly the same succession of strata cannot be expected, though 

 whatever may be included under the indefinitely applied term 

 "formation"* is considered to be continuous. 



Recalling the remarks already made concerning the Lower 

 Carboniferous, it will be remembered that there was abundant 

 evidence for believing that over the region of the Upper Mis- 

 sissippi basin the Saint Louis seas extended northward nearly 

 to the present Iowa-Minnesota line ; that at the beginning of 

 the Kaskaskia epoch a considerable elevation of the land took 

 place, pushing the shore line several hundreds of miles to the 

 south, even as far as the site of the present city of Saint 

 Louis. During this time there was considerable subaerial ero- 

 sion over all the Iowa and northern Missouri areas — shore 

 deposits being laid down along the line of the Mississippi 

 river in southeastern Missouri and southwestern Illinois, and 

 open-sea deposits farther southward, and probably also west 

 of the Missouri river. 



A new period of subsidence setting in closed the Lower 

 Carboniferous in this part of the American continent. On the 

 south, with the Ozark uplift probably above the sea-level, and 

 connected or separated only by narrow, shallow straits with 

 the land aroand the present mouth of the Missouri, and on 

 the east and north with a rise of moderate elevation, the broad 

 basin-shaped lowland, inclined westward toward the open sea, 

 was especially well adapted for the formation and preservation 

 of coal deposits, as the depression continued and the waters 

 of the sea gradually encroached upon the land. In many 

 places the bottom of the broad basin being kept not far from 

 sea-level, slight oscillations allowed the land surface to appear 

 and thus change the local conditions of deposition. The con- 



Geol. Sur. Missouri, Prelim. Eep. Coal. Jefierson City, 1892. 



