In this article the results of a pollen analytical investigation of a section in the tropical lowland of Colombia are discussed. The section has been taken from a lake in the lower course of the River Magdalena (fig. 1). This lake, called ”Cienaga de Morrocayal”, is situated about 20 metres above sea-level; the section represents the greater part of the Subatlantic, and in the course of this period there was a succession of humid and drier periods. These fluctuations seem to represent a cyclic phenomenon. Two C14 analyses of charcoal-samples from the peatlayers, found in this section, showed that these layers were formed at about 1470 A.D. and about 1230 A.D.