Spencer — Great Canyon of the Hudson River. 15 



into an embayment or wider valley which also receives that 

 from the Connecticut, now discovered to a depth of about 6000 

 feet for the first time, but without details to describe its form. 

 In cutting through the continental bench, at 3000-3500 feet 

 beneath sea-level, the floor of the canyon is between 6000 and 

 7000 feet below the surface of the ocean. The valley is contin- 

 uous to a point 71 miles from the head of the gorge and where 

 it is recognizable at a depth of about 9000 feet. 



The canyon and valley discovered to the great depth shown, 

 incising first the level continental shelf, (in which it turns twice 

 at right angles), and then coursing down the great continental 

 slope, is now taken as a gauge for measuring a late high con- 

 tinental elevation of the region to the extent of 9000 feet. 

 This is following out the lines of Dana, Lindenkohl and other 

 students of the submarine channel, in that they considered it a 

 drowned land valley. I have analyzed every other known 

 possible cause of its origin. So great are the probabilities 

 and so long have these been accepted unquestioned, that very 

 strong proof would be required to modify this view. 



The period of the great elevation has been found to coincide 

 with that of the early Pleistocene. Since then there has been 

 a subsidence to somewhat below the present level, followed by 

 a re-elevation of 250 feet as seen in the shallow channels of 

 the shelf. With other minor changes, the region is now sink- 

 ing at the rate of two feet a century. 



This canyon feature at our door corroborates the great 

 changes of level worked out most extensively by Hull of 

 Britain, Nansen of Norway, and myself here and in the West 

 Indies, following methods which the father of geography, 

 Prof. J. P. Lesley, predicted in 1888 "must throw light on the 

 whole subject of elevation and subsidence, as applicable to the 

 entire area of the United States." 



