SUSQUEHANNA, DELAWARE, AND LAURENTIAN CHANNELS 211 



subject of this paper to be more fully elaborated. The channel of Nar- 

 ragansett bay is also traceable across the sub-coastal plain. 



Laurentian and other Channels 



South of Long island and New England evidence of similar channels 

 passing into coves or canyons and gulfs frequently recurs. The gulf of 

 Maine is a broad valley in the submerged plain, with several channels 

 converging toward it, as has been mentioned ; but by far the grandest 

 of all the valleys traversing the drowned plains of the continent is that 

 of the Laurentian. 



The Laurentian channel from the mouth of the Saguenay extends for 

 900 statute miles before reaching the edge of the continental shelf. 

 Soundings in the Saguenay fiord reach to a depth of 882 feet, but below 

 this point the Saint Lawrence is filled so as to have a depth of scarcely 

 more than a hundred feet; however, 35 miles farther down it reaches to 

 702 feet, beyond which the soundings so far taken show a somewhat less 

 depth. A short distance still farther on a depth of 1,128 feet is shown. 

 In the gulf of Saint Lawrence, below the mouth of the river, the depth 

 is 1,368 feet. Even 500 miles beyond this point the incomplete soundings 

 do not reveal a greater depth (1,350 feet), but there are intermediate 

 measurements reaching to 1,878 feet, which show the need of fuller 

 soundings or suggest that the lower part of the course is obstructed 

 probably in part by drift. For the last 140 miles before reaching the 

 edge of the continental shelf the soundings do not touch the bottom, and 

 consequently are insufficient for knowledge of the full depth. Eventually 

 they show that the valley enters a deep amphitheater or gulf indenting the 

 border of the continental mass. The floor of the gulf of Saint Lawrence is 

 generally submerged from 200 to 250 feet, or where it has been dissected 

 the depth may be 200 feet greater, as on the margins of the coastal plains 

 or banks. Through this floor the course of the Laurentian valley is 

 strongly marked, and has a general breadth from 50 to 70 miles, or 

 somewhat greater where the tributaries enter it, the most important 

 being the twin valleys from the north of Anticosti (Anticostian) and 

 that from the straits of Belle isle (Esquimau), north of Newfoundland. 

 This valley has already been previously described by the writer,* being 

 the first of his papers on submarine valleys. 



Another class of channels incising the submerged plains should be 

 noted. These are the fiords extending from the bays of Newfoundland. 

 Thus that of Placentia bay has a depth of 846 feet and that of Trinity 



♦J.W.Spencer: High elevations preceding the Plpistocene period [in America]. Bull. Geol. 

 See. Am., vol. 1, 1889. 



