16 Annals of the Carnegie Museum. 



northern foothills, and contains a greater percentage of non-deciduous 

 trees, and in some places along the southwestern portion it only per- 

 sists on the narrower ridges as islands in the humid forest flowing 

 down from above and joining that of the littoral. 



The humid forest of the Magdalena basin differs decidedly from 

 that on the north coast, which is not properly a lowland forest, but 

 consists almost entirely of species ordinarily found at higher alti- 

 tudes, and which have descended from above on account of the greater 

 humidity and consequent lower temperature of the lowlands and foot- 

 hills on this side. This mountain forest is composed of taller trees, 

 set more closely together, with less undergrowth, and supports a much 

 more limited fauna than the forest of the Magdalena basin. The lat- 

 ter is composed of fewer large trees, more undergrowth, vines, and 

 succulent-leaved plants, with a corresponding abundance of insect life 

 and of fruits to support the more varied and abundant fauna. 



The Magdalena Delta. — Practically the entire delta system of the 

 Magdalena is involved in the section between the main channel and 

 the Cienaga Grande. It is very evident, even to the casual observer, 

 that the area now occupied by the latter, together with the network 

 of lagoons lying between it and the river, was at one time, doubtless 

 in the present geological epoch, a portion of the Caribbean Sea, shal- 

 low perhaps, but nevertheless an arm of the ocean. It is also evident 

 that this area, as well as the littoral to the eastward, has been raised 

 at no very remote period. The proof that this uplift has been compara- 

 tively recent is present in the form of numerous small saline areas 

 on the western littoral, within a few miles of the foot of the hills 

 around Rio Frio and farther south, which are many miles from the 

 present shore-line of the Cienaga Grande. The steady stream of sedi- 

 ment carried down by the Magdalena and the rivers draining the 

 western slopes of the Sierra Nevada, which has been pouring into the 

 Cienaga Grande for past centuries, is gradually filling up this brackish 

 lake. Mangroves have secured a foothold on all sides, thus holding 

 the sediment and aiding the process of filling in. There are thou- 

 sands of acres of mangrove swamp today in this region, interspersed 

 with endless waterways, affording cover and food to myriads of aquatic 

 and semi-aquatic birds. 



Savannas. — The savannas of the Rio Cesar Valley are extensive, 

 and reach up over the foothills and even into the Sierra Nevada it- 



