of the Eastern States. 247 



which they extend, it is evident that this formation cannot' be 

 less than 25,000 feet in vertical thickness. This is equivalent 

 to saying that a mass of stratified shales and sandstone, at least 

 25,000 feet thick, has been removed by denudation from all the 

 country which separates these two formations. This does not 

 imply, however, that a mountain as high as the Himalayas once 

 stood over the site Of New York city. 



As soon as the forces of upheaval had brought to the surface 

 the bottom of the estuary in which these rocks were formed, 

 the waves would begin to cut away the shore, and the rain, and 

 perhaps the frost, to disintegrate and carry off the material 

 exposed to atmospheric denudation. The degradation of the 

 Triassic sandstones and shales, wherever exposed, must at all 

 times have been rapid. The material which now forms the sur- 

 face in these regions is very readily disintegrated. The layers of 

 shale are usually so incoherent as to be easily picked to pieces 

 with the fingers. It is evident that beds of this character can- 

 not withstand for any considerable time the destructive action 

 of the elements, before which even the most rugged mountains 

 are constantly crumbling away. 



Large portions of the country composed of Triassic rocks are 

 scarcely above the level of high tide. The average elevation 

 of the surface of this formation in New Jersey, exclusive of the 

 trap ridges, is probably less than one hundred feet. Even at 

 the present day, when the denudation is nearly at a mini- 

 mum, all the rivers and brooks become turbid and loaded with 

 sediment whenever a heavy shower passes over the country. 

 The carrying power of these streams would be greatly increased 

 were the country more elevated ; and the degradation of their 

 basins would be proportionately accelerated. 



These rocks, however, which yield so readily to denudation 

 at the present time, are the older and doubtless the more com- 

 pact members of the Triassic series. The beds that composed 

 the surface of this formation were probably much less compact, 

 and when first upheaved conld offer but little resistance to 

 wear. The upper portion of the area upheaved, too, may have 

 been fractured in a manner similar to that which took place in 



