In profiles E-17 and E-18 the continental slope becomes gentler, and only in the upper 500 fathoms of E-18 does the gradient exceed 1:25. The upper continental rise is about 60 miles wide with depths predominantly about 1600 fathoms, and the lower continental rise lies at about 2100 fathoms and is very smooth. [Illustration: FIGURE 19.--_Continental-margin provinces: Type profiles off Northwest Africa_] Profiles E-19, E-20, and E-21 cross the continental margin off Dakar and the Cape Verde Plateau which rises from the lower continental rise. The Cape Verde Plateau consists largely of the coalescing bases of the volcanic Cape Verde Islands. The lower continental rise and the abyssal plain reach their maximum width at this latitude. The width of the ocean, the width of the Mid-Atlantic Ridge, the width of the abyssal hills, and the depth at the axis of maximum depth all reach their maximum values for the North Atlantic at this point. The characteristics of the continental rise in this sector are listed in Table 2. The reliability of these figures is much poorer than those given for northeastern United States, owing to the smaller number of profiles in this sector. TABLE 2.--_General characteristics of the continental rise northwest Africa Sector_ Values measured from Profiles E-11 to E-21 ==================================================================== Depth Segment Upper edge Lower edge Gradient Width ==================================================================== Upper continental rise 1 1200 ± 200 1500 ± 200 1:90 ± 30 30 ± 10? 2 1500 ± 200 1600 ± 200 1:200 ± 100 30 ± 15? 3 1600 ± 200 1800 ± 100 1:100 ± 50 25 ± 15? Lower continental rise 1 1800 ± 100 2000 ± 100 1:400 ± 200 75 ± 50 2 2000 ± 100 2000 ± 100 1:1500 ± 500 150 ± 50 3 2000 ± 100 2700 ± 100 1:500 ± 200 200 ± 50 Abyssal plain 2700 ± 100 3000 ± 75 1:1250 ± 250 200 ± 50 --------------------------------------------------------------------