36 Professor Spencer — Continental Elevation. 



great elevation of perhaps two miles or more in height, continuing 

 only long enough to allow the streams to dissect the margins of the 

 tablelands, and form amphitheatres belonging to the new base-level 

 of erosion. While the great depressions shown in the soundings 

 may have in part been occasioned by an exaggerated oceanic sub- 

 sidence along the line of the continental margin, yet amongst the 

 West Indies it has been found that the actual depression has exceeded 

 two miles. Although the deeper valleys of the north may be less than 

 a hundred miles in length, their slopes are no greater than those of 

 the valleys descending fi'om the Mexican plateaux. 



From the generalization of facts just given, the conclusion is, that 

 the high continental elevation of the Antillean region extended 

 northward in Eastern America, of which supporting data have been 

 collected as far as Labrador. 



Submerged Plateau of the North Atlantic. 



If the analytical methods which have revealed the drowned 

 valleys of the American coast be applied to the well-known North 

 Atlantic plateau, similar valley-like phenomena will be discovered. 

 While there are numerous soundings across the Atlantic, in the 

 region of latitude 52°, the lines of soundings to the north are too 

 far apart to everywhere afford detailed study of the submarine 

 features ; except that they show an extensive submerged plateau 

 (from 7,000 to 9,000 feet) rising northward to the Iceland ridge, 

 beyond which it again descends rapidly to depths of 12,000 feet, 

 and west of Spitzbergen, 15,900 feet. The summit of the plateau, 

 between Greenland and Norway, is submerged scarcely more than 

 1,200 feet. However, across the summit there are deeper channels, 

 from the cols of which, valleys trend in opposite directions, like 

 those amongst the West Indies or in the Straits of Florida. These 

 cols are now submerged : that between Greenland and Iceland, to 

 1,974 feet; between Iceland and Faroe, 1,814 feet; between Faroe 

 and Shetland, somewhat more than 3,000 feet ; and between Shetland 

 and Norway, about 1,000 feet. The southern margin of this plateau 

 (in the region of latitude 52° N.) is indented by embayments and 

 amphitheatres, similar to those of the border of the American 

 plateau. From the comparatively numerous soundings upon the 

 summit of the divide, and in the adjacent Arctic sea, the valleys 

 from the cols just mentioned, and many others, can be traced to 

 abyssmal depths. Thus, that between Greenland and Iceland 

 descends rapidly from a depth of 2,000 feet to 6,642 feet, and may 

 be followed to a depth of 9,000 feet. The valley in the opposite 

 direction from the same col, extends northward, and receives the 

 tributary from the Scoresby Sound (which is 1,800 feet deep far 

 -within the Greenland mass). In latitude 74°, there is a remarkable 

 amphitheatre of 5,520 feet in depth; and just south-west of Spitz- 

 bergen, a similar amphitheatre of 8,100 feet in depth is found where 

 the plateau is submerged only a few hundred feet. Spitzbergen and 

 Norway are connected by a plateau which is generally depressed to 

 less than 1,200 feet. From it valleys descend to the Greenland sea. 



