The writer's previous paleogeographic and geotectonic studies indicated that South America and Africa were separate continents by Early Devonian time. The recent discovery of marine Ordovician-Silurian faunas in South Africa suggests that separation of the continents may have been even earlier.

Field studies of transcurrent faults on the South American continent show that some of these faults--particularly those in the equatorial zone--probably are related genetically to the large fracture zones which cross the mid-ocean ridges. Several of the continental fault zones are as old as Precambrian or Eopaleozoic.

Therefore, the writer believes that the Mid-Atlantic Ridge and the associated equatorial fault zones already were in existence by Precambrian-Eopaleozoic time. Continental drift, probably related to movements on the transcurrent faults, gradually widened the gap between the continents from Precambrian time to the present, but the Mid-Atlantic Ridge maintained a constant position with respect to South America and Africa. Detailed field studies on the two continents ultimately will provide better dating of the most critical faults and, hence, will determine more accurately when continental drift began.