Northwest African Sector.--The continental margin from northwest Morocco to Dakar is remarkably uniform and rather closely resembles the northeastern United States sector. The continental shelf and slope are well developed (Fig. 19). The shelf is 15 to 70 miles in width and thus is somewhat narrower than either the North American shelf or the Anglo-French shelf. The shelf break ranges from 50 to 80 fathoms. The continental-slope gradients range from 1:15 to 1:40 and are thus somewhat less steep than in the American sectors. Prominent benches are common at 300, 600, 850, 1200, and 1600 fathoms. The continental rise is well developed and is compound. The main contrast between the North African and American sectors is the greater width of the African continental rise. Off northeastern United States a line of isolated volcanic peaks cuts across the continental rise and abyssal plain. In the North African continental margin volcanic peaks are larger, more numerous, and lie in coalescing lines or along ridges. The Cape Verde and Canary groups lie in the continental rise near the outer edge of the upper continental rise. All provinces except the continental shelf widen from Gibraltar southward toward Cape Verde. On profile E-11 off Casablanca the distance from the shelf break to the lower continental rise is only 50 miles as compared with a similar measurement of 500 miles at Cape Verde. Off Casablanca the continental slope extends to 1400 fathoms where the gradient drops to less than 1:40 from 1:10-1:20 on the continental slope. The upper continental rise which widens to more than 100 miles farther south is only poorly developed off Morocco. No other deep-sea echo-sounding profiles are available for the Moroccan continental margin. Surveys of the continental slope made by the French Hydrographic Service during the past few years will, when published in full, undoubtedly provide much valuable information on the topographic benches in this important area (Grousson, 1957). [Illustration: HEEZEN _et al._, PL. 8 FIGURE 1. CONTINENTAL RISE WEST OF ST. NAZAIRE, FRANCE FIGURE 2. BISCAY ABYSSAL PLAIN. NOTE SMALL MID-OCEAN CANYON FIGURE 3. BISCAY ABYSSAL PLAIN PDR RECORDS EUROPEAN CONTINENTAL RISE AND BISCAY ABYSSAL PLAIN Depth in fathoms.] [Illustration: Heezen _et al._, PL. 9 FIGURE 1. SMALL-SCALE ROUGHNESS, UPPER CONTINENTAL RISE FIGURE 2. ROLLING TOPOGRAPHY, UPPER CONTINENTAL RISE FIGURE 3. CAPE VERDE ABYSSAL PLAIN FIGURE 4. ABYSSAL HILLS] [Illustration: Heezen _et al._, PL. 10 PDR RECORD OF ABYSSAL HILLS, SOUTHEAST OF BERMUDA RISE Note sub-bottom echos from beneath intermontane basin floor. Depth in fathoms.] [Illustration: Heezen _et al._, PL. 11 Area of each photograph is about 6 by 8 feet.