Ampiiii!ians and Reptilks of Santa Marta 



19 



row, even knife-edged, the crests often being btit a narrow wall of rock, in 

 places but a few feet in width along the crest. As the higher altitudes are 

 approached, and one emerges above the "cloud zone." where the precipita- 

 tion is less, the ridges become broader and more rounded, with remains of 

 plateaus and gentle slopes. The valleys are broader and shallower, and on 

 the vast paramos surrounding the snow peaks are to be fotmd great undu- 

 lating tracts of open moorland, broad valleys, and gentle slopes, with many 

 small, picturesque lakes. 



These mountain lakes were possibly caused by glacial action in the 

 remote past, and many of them have been nearly filled with silt from above 

 in comparatively recent times, but at the present day no true glaciers exist 

 in the Sierras, to my personal knowledge, unless some very small ice masses 

 are included under the term. 1 doubt whether any very large glaciers ever 

 existed in the Sierra Nevada de Santa Marta, since I have been able to 

 identify no moraines. I suspect the cause of this absence of glaciers to be 

 the complete isolation of the range and the lack of great buttressing foot- 

 hills and mountains such as abound in the Andes. The rapid and unopposed 

 ascent of the superheated air from the lowlands and its direct action on 

 the snow masses above cause a much higher temperature and higher snow- 

 line than would otherwise be the case at these altittides. 



The topography of the Sierra Nevada de Santa Marta might be con- 

 sidered to indicate that the range is young, but this does not necessarily 

 follow. Traces of volcanic action are wanting and the exposed strata show 

 clearly that the range has been thrust up. The exposed rock is largely 

 granite and in the greater part of the region the subsoil is a peculiar decom- 

 posed granite, abounding in fine particles of mica. While clay deposits are 

 present in many districts, they are decidedly less common than the decom- 

 posed granite. I have seen limestone in only one small district, on the road 

 between Fonseca and San Juan de Cesar, where the road skirts the base- of 

 the foothills. This limestone area is but a few miles in length (east and 

 west), although it may extend far out into the valley. 



The narrow knife-edged ridges in many places seem to be the result 

 of great vertical masses of hard rock which resist erosion along the tops 

 of the divides and maintain the steep slopes. Ridges composed almost 

 entirely of great masses of boulders and solid rock are very common. In 

 addition to the resistance of the rocks and soil to erosion, it must be remem- 

 bered that the east, north, and west slopes of these mountains from the 

 lowlands to the timber line are clothed with a dense forest growth, and that 

 on the south slopes, while the forest growth is largely absent and the topog- 

 raphy is nearly the same as on the other slopes, the ridges are inclined to 

 be broader and more rounded. The conditions thus seem to favor the per- 

 sistence of a youthful topography. 



Climate: The seasons are more or less the same on the different slopes 

 and the contiguous lowlands, although the humidity and the temperature 

 vary greatly on the different exposures, due principally to the trade winds. 

 The surrounding lowlands possess the usual tropical heat of these latitudes, 



