Fig. 4. —Location of North Brazilian Ridge and other major physiographic features. Mid-Atlantic Ridge is schematically shown and large hachured area represents part of ridge shallower than 3,500 m. Seamounts near continent are shown as small cross-hatched areas in which depth is less than about

Fig. 5. —Highly schematic and hypothetical relation of North Brazilian Ridge to fracture zones in equatorial Atlantic. Certain parts of ridge are represented as fracture-zone extensions (shown in black lines); others (shown as stippled areas) represent other bathymetric features

Fig. 7. —Selected seismic profiler traverses of North Brazilian Ridge. Location of each profile is given in Figure 3 . Arrows point to most prominent subbottom reflecting horizon observed in area. Profiles E and I represent extremes in topographic relief of ridge.

Fig. 11. —Bottom photograph on outer flank of North Brazilian Ridge. Area represented by each photograph is about 2 × 3 m. Frame 1 of station V25–14 is about 2 × 1.5 m, but scale is same as in other photographs. Locations of stations are given in Figure 10D . V16–70 is on flank of Mid-Atlantic

Fig. 12. —Bottom photographs on each side of North Brazilian Ridge. Area represented by each photograph is about 2 × 3 m. Locations of stations are given in Figure 10D .

Fig. 13. —Bottom photographs at a steep inner flank of North Brazilian Ridge. Area represented by each photograph is about 2 × 3 m. Locations of stations are given in Figure 10D .

Table 1. Possible Modes of Formation of the North Brazilian Ridge

Fig. 9 —Seismic profile E-E′. Location shown on Figure 2 . Reflector M/P is Miocene-Pliocene; EM is early Miocene(?). NBR = North Brazilian Ridge. From Kumar et al (1976 ).

Fig. 14. — Left : Line drawing of normal-incidence seismic-profiler traverse along axis of North Brazilian Ridge near Profile M. Acoustic basement is indicated by cross-hatched reflector on left of normal-incidence profile (in Ceara abyssal plain just outside North Brazilian Ridge near 40°W. long

Fig. 16. —Topography, free-air anomaly, and total-intensity magnetic anomaly along four closely spaced traverses of central North Brazilian Ridge. Free-air anomaly center curve for each profile. Topography is shown cross-hatched and magnetic anomaly is solid line. Note apparent random character

Fig. 15. —Schematic bathymetric profile on continental margin and North Brazilian Ridge. Nearby thermograd stations have been projected onto profile. Composite heat-flow profile across margin and ridge is shown at top. Locations of stations are given in Figure 10C . Ridge does not serve

FIG. 16 —Seismic record (C-17) from continental shelf (left), across Ceará Plateau, and adjacent continental rise and North Brazilian Ridge (right). Flank is deeply incised by gullies. At continental rise is evidence for shallow tectonic movements.

Fig. 19. —Comparison of two sections of continental margin of east coast of North America (from Drake et al ., 1958), and one projected section from North Brazilian Ridge. Scale and vertical exaggeration are same for all profiles. Sediments are indicated by stippled pattern. Inferred crystalline

-second level is indicated for each profile by bold carat. Profiles are aligned on North Brazilian Ridge as shown in Figure 4 . Arrow indicates only seismic traverse of margin that did not display any ridge structure. Hachured reflectors indicate where acoustic basement was observed. Stippled parts

, eastward extension of North Brazilian Ridge cannot be traced to profile VII. Vertical scale is in seconds. Carat represents 5-second depth.

Fig. 8 —Seismic profile C′-C, D′-D, and F-F′. Locations shown on Figure 2 . Reflector M/P is of Miocene-Pliocene age. EM on profiles C′-C and D′-D is early Miocene(?) age, and on F-F′ is early Miocene. NBR = North Brazilian Ridge. Profiles C′-C and D′-D are from Kumar et al (1976 ); profile F-F