248 The Physical History of the Trias 



the depressions along the sides, and the work of erosion may 

 thus have been greatly aided. The fissure which we have de- 

 scribed as occurring at Arlington, may be one of such a series. 

 The suggestion also presents itself that the course of the Hud- 

 son might have been directed by this same means. When we 

 remember that these beds have been exposed to denudation 

 since the Triassic period, and have passed through the tremen- 

 dous destruction caused by the glaciers and glacial rivers of the 

 Ice Epoch, we cease to question the fact of their former great 

 extent, but wonder, rather, that a vestige of them still remains. 



It has been suggested as an objection to the extension of the 

 Triassic beds over the southern part of New York and the 

 western portion of Connecticut, that the crystalline rocks of 

 this region show that they have suffered greatly from erosion, 

 and must, therefore, have existed above the level of the ocean, 

 and been subjected to degradation, for many ages. The view 

 that this area has suffered denudation by the action of the ele- 

 ments, is without doubt correct. But that this erosion took 

 place during the Triassic period, is far from having been 

 proved. These crystalline rocks are supposed to belong to the 

 Eozoic age, and, so far as we are now able to judge, existed as dry 

 land throughout the Silurian, Devonian, and Carboniferous ages. 

 During the Triassic period, however, if our views are correct, 

 this surface was submerged, as already stated, and the Triassic 

 beds deposited on the eroded surface of the crystalline rocks 

 beneath. This ancient land surface was also again exposed to 

 denudation, after the soft Triassic sediments had been removed. 



In describing the 'extent of the degradation in the Uintah 

 Mountains,* Major Powell states that the upheaval of these 

 mountains began at the close of the Mesozoic age, and that the 

 total amount of upheaval in the axial region was more than 

 30,000 feet. " Second, pari passu with upheaval, degradation 

 progressed ; and in some places along the axial portions of the 

 region this degradation amounts to more than 25,000 feet, and 

 the mean degradation is three and one-half miles ; and from 

 the entire area there has been a total degradation of 7095 cubic 



~* Geology of the Uintah Mountains, p. 201. 



