The North Savannas basin in southern Guyana, South America, is a rift valley filled with several kilometers of sediments consisting at the top of the Takutu Formation of Jurassic to Cretaceous age. This Takutu rift valley is part of a dislocation system which runs eastward from the interior of the continent, curving to the northeast toward the Atlantic coast. If the continents of Eurasia and Africa are closed with the Americas in the position assumed for Paleozoic time in the hypothesis of continental drift, then the Takutu rift valley dislocation is found to project to the northeast into the line of the presumed ancestral North Atlantic rift. The Bolivar dislocation zone in eastern Venezuela, which possibly extends for some 1000 km, also projects east-northeastward into the same line. In West Africa the Gao trench and Niger lineament project south-southeastward into the presumed line of an ancestral South Atlantic, and the faulted trough of the Benue River valley projects westward into the segment of an ancestral rift between Brazil and West Africa.
Evidence also indicates that all four of these lines of fundamental faulting date back to Precambrian time, and it is suggested that they represent important mantle lineaments of which certain segments have become the locus of ocean spreading. The extensive spreading necessitated in these oceanic segments to account for continental drift is in contrast to the minimal distension observed in the segments which remain in sialic crust.