212 ILLINOIS STATE ACADEMY OF SCIENCE 



gence of sufficient relief to permit ground water to de- 

 velop subsurface channels and- caverns with surficial 

 sinks. Then there was a complete relative submergence, 

 during which the sinks were iilled with black shale, but 

 whether this relative submergence was of Devonian or 

 Pennsylvanian age must yet be determined. A sec- 

 ond relative emergence permitted the development of a 

 second generation of sinks, some of which were formed in 

 the rock forming the walls of those developed during the 

 first emergence. A second relative submergence, un- 

 doubtedly Pennsylvanian in age, provided opportunity 

 for these sinks in turn to be filled, this time with a green 

 shale. 



Since that time there have been relative emergence 

 and subsequent erosion of such overlying formations 

 as may have been deposited, bringing the area to its 

 present altitude. So far as the writer is aware, modern 

 or Pleistocene karst topography nowhere occurs on the 

 Niagaran dolomite, although its altitude would seem to 

 permit such occurrence; in Paleozoic times there were 

 two distinct periods or epochs when a youthful karst 

 topography was well developed in the same formation. 

 "Whether this is due to a decrease in the solubility of the 

 Niagaran dolomite or to some other cause is at present 

 a matter of conjecture. 



