The great basins of the Orinoco, Maracaibo, and the Rio Magdalena occupy much of the general area of northern South America. What relations may have existed among these several basins in the past, or even within the limits of the Tertiary, can only be surmised in the present state of geologic knowledge, though there are grounds for suspecting that throughout the Tertiary era all shared in the major movements of uplift and subsidence, with individual differences. It seems probable that there was intimacy, if not actual connection, between some of these basins during the early Tertiary. All seem to have had somewhat similar drainage relations to the region lying between, but to what extent each of them transgressed such land area as existed there during the Tertiary is not yet known. At the present time the high cordillera of the eastern Andes lies between or borders on these several . . .