356 Professor E. Hull — Submerged Terraces S^ Valleys, 



V. The English Channel Eiver and the " Hurd Deep." — The 

 course of the river which drained the area of the English 

 Channel can generally be traced by a curving line of depression 

 from its source near the Straits of Dover to the margin of 

 the great escarpment, where it cuts deeply into the rock in the 

 form of a gorge or caiion. Owing, probably, to silting up by 

 sediment, the course is less evident than it would have been had no 

 sediment been deposited. But at one part of its course its position 

 is still clearly defined on the chart for a distance of 70 miles under 

 the name of the " Hurd Deep." This is a nearly straight E. and W. 

 gorge about 4 to 5 miles across, and at its deepest part 354 feet 

 below the general floor of the sea bed.^ Here, we may suppose, the 

 channel has been kept open and free from sediment, unlike the 

 portions of the river valley above and below. The cause of this 

 dissimilarity of conditions is not far to seek. On looking at the map 

 it will be seen that the " Hurd Deep " lies in the narrowest part 

 of the channel west of the Straits of Dover, between the Isle of 

 Wight and Portland Bill on the north, and Cape de la Hague and 

 Cape de Barfleur on the south. Above and below this strait the 

 channel broadens out to about twice its breadth between these 

 points ; hence the tidal currents have here extraordinary force 

 and swiftness, owing to which the sediment, deposited above and 

 below, appears to have been prevented from settling down and 

 filling up the gorge of the old river. The general outline, the 

 direction and position of this remarkable rift, all point to the " Hurd 

 Deep " as a river channel which has been cut down into the solid 

 rock, and is bounded by steep, or precipitous, clifi"s i-esembling on 

 a small scale the American canons. The two submarine rivers here 

 described must have exceeded in size any of our existing streams, 

 and we may infer entered the ocean in a succession of grand cascades.^ 



VI. Comparison icith the American Submerged Platform. — In my 

 former paper ^ I described briefly the results arrived at by Professor 

 Spencer and other American geologists regarding the " drowned " 

 plains, escarpments, and river valleys lying outside the North 

 American coast, and I showed that they consist (1) of the 

 " Continental Shelf," stretching out into the Atlantic as far as the 

 100-fathom line, or thereabouts, when it breaks off along an 

 escarpment, descending to a depth of 450 or 500 fathoms. This 

 escarpment is then succeeded by a second and more extensive 

 terrace, known as " the Blake Plateau," which in turn terminates 

 along a second grand escarpment descending to the abyssal depths of 



1 Tlie deepest point shown by the soundings is 95 fathoms, Avhile the bordering 

 level of the sea bed is 36 fathoms. 



^ Man was not present to view the scene presented by the British Isles at this 

 time ; but we may easily reproduce before our minds its grandeur as visible from the 

 ocean at a distance of a few miles from the coast. In front would rise the lofty 

 terraced cliffs, several thousand feet in height, and stretching away to the north and 

 south in bold headlands and wide bays till lost to sight in the distance ; while, 

 planted on the nearly level terrace above, would be seen in the far distance the 

 mountain heights robed in a white mantle of snow. 



3 " On Another Possible Cause of the Glacial Epoch" : Trans. Yict. lust., 1898. 



