21G J. W. SPENX'EK — SUBMARINE VALLEYS 



2,430 feet, where the lateral bank is onh^ 1,020 feet below sealevel. 

 While the drowned col in the straits of Belle Isle is 240 feet below sea- 

 level and the Labradoran channel (here so named) trends northeastward 

 and is seen to become a valle}- at a depth of 1,500 feet, the soundings 

 are too few to mark its further course. From the same col, but extending 

 southeastward, is the Esquimau channel, joining the Laurentian valley . 



SOME FEATURES OF THE CONTINENTAL SLOPE 



It is notable that the embayments into the continental slope in front 

 of the great valleys mentioned are much deeper than would be suggested 

 by the outline of the present shores. The approximation of the Les- 

 leyan and HuUian bays indenting the opposite sides of the last stretch 

 of the submarine continuation of the American continent is such a 

 feature as characterizes the atmospheric erosion of tablelands with their 

 ultimate dissection into separated plateaus. The cul-de-sac, coves, or 

 gulfs are found to indent the border of the continental mass for distances 

 of 8 to 20 miles or more, and even the incomplete soundings show that 

 their width is reduced to even 3 miles, but the}^ enter lower embayments, 

 widening to 5, 10, or even 20 miles or more when far seaward, but yet 

 no wider than the lower reaches of valleys of existing rivers. 



The declivities of some of the greater valleys observed do not show a 

 greater slope than about 100 feet per mile. Except for short tributa- 

 ries from plateau regions, this is too large an amount for normal valleys. 

 The data are insufficient to work out the gradients, as has been done in 

 the case of the Floridian channel, where it is often about a foot per mile 

 for long distances, succeeded by rapid descents from one step to another. 

 However, we find everj^where in the coves or gulfs, indenting the margin 

 of the drow^ned continental shelves, the evidence of abrupt or rapid de- 

 scent from step to step, although we do not know the gradients bet^veen 

 them or of the further descent of the valleys. Such submarine features 

 are repetitions of what may be seen on the tablelands of Mexico and 

 Central America, with the slopes between the steps greatly reduced. 



Geological Characteristics of the Region traversed by the 



Valleys 



From the occurrence of the geological formations of the adjacent coastal 

 plains some inferences of the character of the submerged plains may be 

 formed, which to some extent are sustained by the direct evidence of 

 the materials brought up by the dredges. Thus we can form an idea of 

 the age of the valleys. 



From New Jersey onward to Newfoundland, surface deposits of drift 



