Submarine Valleys and Cafions off American Coast 
depth of the channel is 2300 feet, but this appears to be obstructed by morainic ridges of 200 or 
300 feet in thickness, as should be expected in this region. The submerged Laurentian valley has 
tributaries, the largest coming from the submerged land-tongue between Labrador and Newfoundland. 
From the point taken as the mouth of the St. Lawrence River, its very deep channel extends 
for 700 miles to the margin of the Continental Shelf, 200 miles south of the line of the coast. 
Inside this line a deep cafion begins to trench the border of the Continental Shelf. Here it reaches 
to 3666 feet below the surface, but no soundings have been taken to define: its course down the 
Continental Slope, although the corresponding embayment is shown at lower depths. 
The two distinct features of the Gulf of St. Lawrence are—the long broad valley bounded by high 
cliffs, and the beginning of the cafion at its lower end. Each has had its own history. 
The broad valley was apparently the result of long-continued erosion, when the region stood at least 
2300 feet higher than now, and yet not more than a few hundred feet higher than this amount, so that 
the drainage slope was such that the river cut out its channel down to the level of no erosion; after 
which the denudation only widened the valley to more than a score of miles. 
The cafion trenching its end is characteristic of the new conditions, when the land rose very much 
above the present ocean level. Then the river rushing down the Continental Slope gave rise to the new 
gorge. Compared with the period of the broad valley above, the cafion-making epoch was of very 
short duration. It was terminated upon the waters rising and flooding even the upper valley so as 
to produce the Gulf of St. Lawrence and the submerged river branches above. 
The Gulf basin is mostly excavated out of Palaeozoic formations, but upon the south-western side 
are somewhat extensive sheets of Triassic strata. On the frontal banks of Newfoundland and New 
England the occurrence of Tertiary limestones has been found in dredging operations. Accordingly, 
the completion of this great valley belongs to a late date, although the beginnings of it go back a long 
way in time. 
Land-like Features of the Newfoundland Banks—South of Newfoundland, the Continental Shelf 
extends for nearly 200 miles, with the higher portions forming the “ Newfoundland Banks.” South- 
eastward, these extend seaward for about 300 miles. I have taken the edge of the Continental Shelf 
at the isobath of 450 feet; but at a greater depth the most eastern spur of the American mass extends 
425 miles beyond the land. This is a submarine plateau, surmounted by ridges, the terminal portion of 
which is partly separated from the main mass by indentations or deep embayments and valleys on both 
sides, to which I gave the name of Hullian and Lesleyan Bays! (see Map). This feature is the repetition 
of a well-developed similar one between Honduras and Jamaica, where different stages of dissection, 
according to the width of the plateau, may be seen, even to the complete separation of the terminal 
plateau.? On the land such features are represented in many regions. 
This most eastern sub-oceanic tableland of the continent I shall name in honour of Professor 
Hull, who first reduced to order the data bearing on the submarine valleys of Western Europe, 
thus demonstrating that the features are alike on both sides of the Atlantic. The Continental Slope 
bordering this Hullian Plateau descends to the ocean depths, over precipitous cliffs, thousands of 
feet in height ! 
The soundings on the Newfoundland Banks show the plateau to be indented by many valleys, with 
cafions dissecting the Continental Slope, some of which, however, are of the characteristic form of amphi- 
theatres on the borders of plateau regions. 
Submarine Cations of the Gulf of Maine and of Chesapeake Bay.—In the border of the Continental Shelf, 
_ opposite the mouth of the Gulf of Maine, the Continental Slope is trenched by a deep cafion. It is now 
known to a depth of at least 7020 feet below sea-level. The gorge itself is more than 1500 feet deep ; 
1 See map of “Submarine Valleys of the Atlantic Coast,” Bull. Geol. Soc. Am. vol. xiv. opp. p. 208 (1903). 
2 See map, p. 116, Bull, Geol. Soc. Am. vol. vi. cited. 
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