158 The American Geologist 
March, 190o 
iiels. Nor are such found on the small-scaled charts of the 
Challenger. The recent suboceanic map by Mr. Huddle- 
ston shows the platform but not the river valleys.. 
The British platform continues onward and in front 
of Brest it is 130 miles wide. In the bay of Biscay it 
diminishes to 100 miles; but on the north coast of Spain, it 
is reduced to 20-30 miles in width. West of Portugal its 
breadth is generally from 30 to 40 miles. It increases 
southward till off cape St. Vincent it widens out into a 
succession of terraces. Along this coast the margin nearly 
coincided with the 200-fathom line. 
From the English channel to Gibralter, the floor of the 
platform is covered with gravel, sand, clay and occasional 
boulders with occasional mollusk remains, while the oceanic 
floor is a calcareous marl. From Rockall for a distance 
of 2,000 miles along the coast line the g reat declivity (con- 
tinental slope) is intersected with channels which cross 
the continental platform from the great terrestrial rivers. 
Such a slope has its counterpart in the borders of the raised 
plateau of Mexico (citing the reviewer). The gradient of 
the declivity varies from four to twenty-one degrees or in 
one case thirty-six degrees. These are the mean results 
for each section, yet in many cases the actual slope is made 
up of precipitous cliffs and gentler gradients. But fuller 
soundings are much to be desired to complete the detail. 
Among the channels deeply trenching the continental 
platform Prof. Hull describes those of the Loire (which 
takes the form of a double canyon, and is traceable to a 
■depth of 9,000 feet) ; the Gironde and the Adour. This 
last is the greatest of them.* At six miles from the shore 
it passes into the Fosse de Cap Breton incising the platform 
to a depth of 702 feet, where it is covered by 348 feet of 
water. At 15 miles it receives a tributary channel from 
the south. It rapidly deepens into a canyon with walls 
4.000 to 6,000 feet high, and ultimately opens to the floor of 
the ocean at 9,000 feet. It bifurcates and encloses a tract of 
■shallower ground. It was considered by Alphonse Milne- 
Edwards as the ancient bed of the Adour. South of it the 
♦•Explored by the Travailleur Ex petition in ISSO. Bull. Geog Soc. 
Paris, vol. iii, p. 113, 1882. 
