216 H, p. GUSHING UNCONFORMITY AT BASE OF BEREA GRIT 



siderable break or else that the break is a peculiarly elusive one, hidden 

 in weak and poorly exposed shales in such wise that it is very difficult to 

 detect. If it be true that in the northern Appalachian basin the De- 

 vonian passed into the Mississippian without diastrophic oscillation and 

 sea withdrawal, then the trifling character of the break at the base of the 

 Berea would have no significance; but if this be not true, if diastro- 

 phism be periodic and is to be used as the basis of geologic classification, 

 it is not out of place to urge that this break is of too minor a sort to be 

 successfully used as an argument for drawing the line between two geo- 

 logic systems at its horizon. The immature stage of erosion represented 

 by the channels and the fact that the Berea base rests on the same thin 

 underlying formation all across the State seem to us cogent arguments 

 against the break being other than a most trifling one. 



