790 



DYNAMICAL GEOLOGY. 



der of the State) is a country 50 to 60 miles wide, of open northeast 

 and southwest valleys, with long intervening ridges or mountains 

 shaped by denudation ; and it is called as a whole the " Valley of 



Fig. 1144. 



Cumberland Table-laud, Tennessee ; c, Crab Orchard Mountain ; 2 to 9, as on p. 142. 



East Tennessee," because, owing to the denudation, much of the coun- 

 try is low compared with the equally wide Cumberland Table-land. 

 As described by Safford, the surface of the Table-land is 900 to 1,200 

 feet above the valleys on the east, aud at one point nearly 2,000 feet, 

 and it averages 2,000 feet above the sea-level. In consequence of a 

 fault at its eastern foot, stratum No. 4 (Hudson River) is there in con- 

 tact with 2, or the Calciferous ; and then, just east, another fault has 

 put the latter stratum along side of No. 7, or the Devonian Black 

 shale. 



The Catskill region is another plateau portion of the margin of 

 the Appalachians. The rocks, which are Upper Devonian at top, rise 

 in some of the peaks to a height (as shown by Guyot) exceeding 4,000 

 feet ; and yet they are nearly horizontal, and actually the eastern 

 margin of the great plateau of Southern New York. Denudation, as 

 stated on page 647, has given them their mountain-like shapes ; and 

 the depths of the valleys, as well as the height and boldness of the 

 escarpment facing the Hudson, shows that there has been an immense 

 amount of it. The Uinta Mountains are a broad plateau, 150 miles 

 from east to west (the direction of its axis), on the east of the Wah- 

 satch Mountains, against which they terminate abruptly. There are 

 gentle flexures at the north and south extremities. 



Such facts prove that great plateaus and regions of steep folds may 

 be from one and the same process of mountain-making. The Appa- 

 lachian Mountain region has received part of its altitude since the 

 Appalachian revolution ended ; but relative heights may not be very 

 greatly altered, except through denudation. 



2. Fractures. Faults. — Fractures characterize all mountain regions. 

 Along the axes of folds they are very common. This is especially 

 true of anticlinals, in which the fractures naturally open upward, and 

 were often left gaping, or were filled so as to become the courses of 

 veins. Hence, great veins are often an indication of the centre of an 

 anticlinal. 



