72- Bulletin American Museum of Natural History. [Vol. XXXVI, 



Thus, the great region lying east of the Eastern Andes, the western ex- 

 tension of the Amazonian and Orinocan basins, is separated by this range 

 from the Magdalena Valley. 



This valley, in turn, is walled about by the Eastern and Central Andes 

 and, so far as tropical life is concerned, is accessible only at its northern end. 



The Cauca Valley is similarly isolated and is open only at the north, 

 while the Pacific coast region is shut off at the south by the deserts of south- 

 ern Ecuador and Peru, and at the east by the entire Andean system. Like 

 the Magdalena and Cauca Valleys it, too, is apparently to be entered only at 

 the north. Tropical Colombia, therefore, may broadly be spoken of as 

 consisting of the western portion of the Amazon-Orinoco Basins and three 

 cvl de sacs which debouch on its northern coast. 



To what extent existing faunal conditions are dependent on existing 

 topography, and to what extent they have been brought about by what 

 may be called pre-Andean topography, remains for us to determine. 



Remaeks on the Distribution of Fokests. 



The detailed information which we gathered in relation to the distribu- 

 tion of forests in Colombia will be found in the descriptions of the routes 

 traversed by our expeditions, as well as in the Gazeteer. We covered, 

 however, so comparatively little ground, and conditions change so abruptly, 

 that data are lacking for anything but the most generahzed statements in 

 regard to the extent of the forest areas of Colombia as a whole. The pres- 

 ence or absence of forests, however, has so important a bearing on the 

 boundaries of faunal areas, that from the zoologist's point of view, even 

 generalized statements are of value. 



The Forests of the Tropical Zone. — The Tropical Zone possesses five large 

 areas of heavy, humid forest. Named in order of their importance they 

 are (1) the Amazonian; (2), the Pacific coast; (3), the lower Cauca-Mag- 

 dalena; (4) the Maracaibo Basin, only the western portion of which enters 

 Colombia, and (5) the Santa Martan. 



The Amazonian forest region occupies all that part of Colombia lying 

 east of the Andes and south of the Rio Guaviare. Its northern boundary, 

 therefore, lies just north of the divide between Amazonian and Orinocan 

 drainage. It forms, in fact, the northwestern corner of the vast forests 

 of upper Amazonia which, southward, reach to Bohvia. 



Miller (Expedition No. 5), writing from an elevated position near 

 Florencia says " one has a good view of the-Caqueta-eouHtpjv^.-perf ect oceaa 

 of forest stretching out ahead as far as the eye can see, which, on clear days. 



