CRETACEOUS TENErLAIN IN VIRGINIA. 



561 



far the plateau caii be traced westward cannot cow be stated, for in going 

 westward the rocks become weaker, shales replacing sandstones, and the up- 

 lands are less and less continuous. Much more study, aided by good maps, 

 will be needed before the extension of the peneplain into Ohio and beyond 

 can be determined. 



South of Pennsylvania the evidence is better than in the Ohio valley. 

 The plateau of West Virginia, Virginia, Tennessee and Alabama is well 

 marked ; but, as in Pennsylvania, its upland does not mark a constructional 

 surface: it consists of the obliquely bevelled edges of various beds; and it 



Figure i— Cretaceous Peneplain in the Middle Appalachian Region. 



is in this eroded surface that the present valleys are excavated. The part of 

 the Appalachians in Tennessee contained between the plateau on the west 

 and the great valley on the east consists of faulted rather than of folded 

 Paleozoic formations. Wherever hard beds appear, they rise to a generally 

 even outline and carry it for many miles. Clinch mountain, in Virginia 

 and Tennessee (see figure 4), is a remarkable example of this kind of form. 

 It is the edge of the Medina sandstone, which there, as in Pennsylvania, is 

 the chief mountain-maker. It is well portrayed on the Morristown, Ten- 

 nessee, topographic atlas sheet of the United States Geological Survey. 



