The basaltic rocks from the upper part of the basement of the Atlantic between the Equator and 37°N have major and minor element signatures which correlate with large latitude intervals. 204 compositional basalt types based on electron microprobe analyses of the glassy rinds of pillow lavas fall mainly into two groups of Recent to Eocene age: a 0-29°N group characterized by higher TiO2, NaO2, P2O5/K2O, and lower CaO than a 36-37°N group. Basalt cores from Cretaceous and Jurassic DSDP drill sites suggest migration of the 0-29°N group to the north through time. The higher K2O contents of the 36-37°N group may reflect the influence of a southward longitudinal migration of the postulated Azore's 'thermal plume' magmas. If so, the migration is dammed by the Oceaonographer Fracture Zone, which marks the southern limit of this group. High K2O lavas reappear in the vicinity of the Equator, perhaps reflecting on-going activity of the proposed Sierra Leone or St. Paul's Rocks 'thermal plume'.