GLACIAL SUCCESSION IN OHIO. 1 45 



the ice -sheet from Ohio. A deglaciation interval is believed to 

 have preceded this stage, but as yet, decisive evidence in support 

 of this view is not obtained. 



We may now profitably review what is known concerning the 

 altitude in each stage : 



1. During the earliest advance little of value is known in 

 this region. The scarcity, if not absence, of coarse overwash 

 material seems to indicate feeble drainage and consequent low 

 altitude. It is true that the Split rock and Middle creek con- 

 glomerate indicate powerful water action, but if formed as they 

 appear to have been beneath the ice -sheet, they show little as to 

 the altitude of the land. 



2. During the period of deglaciation following the depo- 

 sition of the earliest drift there appear, from the character 

 of the changes effected, to have been fair drainage conditions. 

 We may presume, therefore, that the altitude was not much 

 lower than the present altitude of the region (800-1000 feet 

 A. T.). 



3. During the period of silt deposition there can be little 

 doubt that the region stood several hundred feet lower than 

 now. 



4. During the formation of the outer moraine of the later 

 drift there were apparently as good drainage conditions as are 

 now afforded in the western Ohio region. 



5. During the succeeding deglaciation interval the erosion 

 effected indicates a fair altitude. 



6. During the formation of the main morainic system the 

 maximum of elevation was probablv reached, there being an espec- 

 ially vigorous drainage at that time, not only in Ohio, but as far 

 to the west as the moraine has been correlated. 



7. During the formation of the later moraines there seems 

 to have been a return to low altitude, and still later the Cham- 

 plain submergence of the coast and St. Lawrence occurred. It is 

 important to note that the Champlain submergence is separated 

 from the submergence which produced the silts of southern Ohio 

 by the periods of high altitude just mentioned, a succession of 



