. JFMAMJ J ASOND JFMAMJJASOND PORT NOILOTH J FMAMJ J A S O N D DASSEN ISLAND LUDERITZ BAY Fig. 3. Mean annual rainfall in inches, at five points on the South-west African coast: Mossamedes (150 12' S.), Walvis Bay (220 56' S.), Luderitz Bay (260 39' S.), Port Nolloth (290 14' S.), and Dassen Island (33° 26' S.). (From data in Royal Naval Meteorological Service and South African Air Force, 1944.) Over the greater part of the area covered by our surveys, the continental shelf, defined approxi- mately by the 200 m. contour, is about 40 miles broad, widening to about 90 miles off the Orange river
. JFMAMJ J ASOND JFMAMJJASOND PORT NOILOTH J FMAMJ J A S O N D DASSEN ISLAND LUDERITZ BAY Fig. 3. Mean annual rainfall in inches, at five points on the South-west African coast: Mossamedes (150 12' S.), Walvis Bay (220 56' S.), Luderitz Bay (260 39' S.), Port Nolloth (290 14' S.), and Dassen Island (33° 26' S.). (From data in Royal Naval Meteorological Service and South African Air Force, 1944.) Over the greater part of the area covered by our surveys, the continental shelf, defined approxi- mately by the 200 m. contour, is about 40 miles broad, widening to about 90 miles off the Orange river mouth, and to 70 miles off Walvis Bay. Off Concepcion Bay, in 240 S., there is a sharp indenta- tion on the shelf edge, and as at Luderitz Bay the shelf is less than 20 miles broad. North of 200 S. the shelf narrows, and between 160 and 130 S. is almost non-existent, the slope falling straightway from the coast into the depths of the Angola Basin. The shelf edge off Bahia dos Tigres is much dissected into deep valleys which extend to depths of 1000 m. The bottom slopes away fairly steeply from the coast to the 100-m. contour along most of the coast- line, and then more gradually to the shelf-edge, forming virtually a submarine plain, a feature most pronounced off the Orange river. From the shelf-edge there is a fairly gradual and constant slope to 3000 m., interrupted only off the Cape Peninsula where deep canyons are numerous between 500 and 3000 m., and in 200 S. where the continental slope is very gradual and at 1000 m. grows into a buttress forming the northern end of the Walvis Ridge. The Walvis Ridge leaves this buttress in a westerly direction at 3000 m., and runs southwards and then to the west again to link up with the central Atlantic Ridge. In 250 S., 6° E. there is a prominent
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