212 J. W. SPENCER — SUBMARINE VALLEYS 



bay 1,494 feet, with their courses apparently obstructed to the amount 

 of 300 and 600 feet, supposedly by drift deposits, in a manner not seen 

 among the channels in more southern latitudes. But fuller soundings 

 may reveal the course of the valleys without so much apparent obstruc- 

 tion. Evidence also appears of the existence of several fiords extending 

 from Newfoundland across the banks, but the soundings are not full 

 enough to work out the old hydrography. A valley (the Labradoran) 

 trending northward from the straits of Belle isle, between Newfoundland 

 and Labrador, is shown to a depth of 1,500 feet, and Hamilton inlet, in 

 Labrador, reaches to 1,800 feet, with its lower portion seemingly blocked 

 in part. These apparent obstructions by drift deposits are of much value 

 as showing that the valleys were formed before the epoch of glacial drift. 

 This inference as to the age of the buried valleys may be carried farther 

 south. 



Among the shallower soundings of the Laurentian valley, already ex- 

 plained by either insufficient exploration or to drift filling, those reach- 

 ing to about 1,800 feet sufficiently establish that the general depth of the 

 valley throughout the greater portion of its length is equal to this amount, 

 while the channels through the jgulf of Maine are not known to have 

 exceeded 1,100 feet. Such valle3^s continue to within a few miles of the 

 edge of the continental margin, where they are abruptly precipitated 

 into coves, ampitheaters, or gulfs. 



The submarine valleys mentioned are continuations of those of exist- 

 ing rivers. Others are not traceable to the modern rivers, because sub- 

 mergence even to their sources, as the Cansoan valley, which heads in 

 the straits of Canso, and the Esquimau and Labradoran, which approach 

 each other in common in the col, now sunken to form the straits of Belle 

 isle, between Newfoundland and the continent. So also the banks of 

 Newfoundland are nearly dissected by the Lesleyan and Hullian ba^^s, 

 all of which are now beneath the Atlantic waters. 



Characteristics of the submerged Continental Slope 



in general 



From the narrowed continental shelf off cape Hatteras there is a rapid 

 descent to 3,096 feet in 7 miles, and then to 9,582 feet in the next 6 miles, 

 without the revelation of any intermediate ledges. This is the most 

 abrupt descent shown in the continental slope. North of this point both 

 the submerged coastal plain and the great continental slope widen rap- 

 idly, as they do southward. Off Nova Scotia the zone of descent is some- 

 what reduced in breadth, and at some points off the Newfoundland banks 



