THE SUB-OCEANIC DEPRESSION, ETC. A421 
surfaces to the extent required for the sub-aerial erosion of 
depressions cutting through the Continental Platform to its 
base would anywhere give such a change of position of 
greater and lesser erosive power as would sufficiently account 
for the admitted disproportion of some submarine depres- 
sions to the respective nearest rivers by the prolongation 
of which it is concluded they have been cut down to their 
present depth. 
The examples most prominently brought forward of this 
disproportion are those of the small depressions opposite to 
the great rivers, the Loire and the Gironde, and the great 
depression called La Fosse de Cap Breton opposite to the 
smaller river, the Adour. 
The Fosse de Cap Breton is in the bed of the great south- 
east angle of the Bay of Biscay, the Gulf of Gascony. It 
commences close to the shore-line adjacent to Cap Breton, 
about ten miles north of the present mouth of the River 
Adour, on the coast of the Landes, and extends westwards 
as a depression in the sea-bottom for a distance of. about 
100 miles. At a distance of six miles from the land it has a 
depth of 1,000 feet from the surface of the sea, and at ten 
miles from the shore-line a depth of 1,200 feet. At fifteen 
miles from the commencement of the depression another 
submarine valley from the mouth of the Adour opens into 
it on the south side, and then the Fosse rapidly deepens, 
assuming, in the words of Professor Hull, “the form and 
features of a grand cafion, bounded by steep, sometimes 
precipitous, walls of rock from 4,000 to 6,000 feet in height, 
and ultimately opening out on to the floor of the ocean at a 
depth of about 1,500 fathoins (or 9,000 feet).” 
The sea bottom on the north side of the Fosse de Cap 
Breton is remarkably different from that on its south side. 
On the north the Continental Platform, commencing with a 
width of thirty miles, widens as it extends northwards, until 
it attams a breadth of about 150 miles off the coast of 
Brittany, while on the south side it is very narrow, at one 
place only six miles wide, and nowhere along the entire 
length of the Fosse of 100 miles is the platform more than 
twenty miles in breadth. Thus the Fosse de Cap Breton is 
approximately parallel with the north coast of Spain and at 
right angles with the southern part of the French shore of 
the Bay of Biscay, the coast of the Landes. 
The adjacent coasts correspond in their physical features 
most strikingly with the sea floor on each side of the Fosse. 
