1904.] Allen, Mammals from Santa Marta, Colombia. 409 



a narrow channel on the east and south and a broader one on 

 the west. This almost insular character of the region is im- 

 portant and should be borne in mind. It may be noted that 

 the geological formations of the Sierra, as far as we have any 

 knowledge'of them, show no direct relations with those of the 

 Andes. There are no active volcanoes, and no extinct ones 

 are certainly known. Earthquakes are common in the Andean 

 chain and their vibrations are sometimes felt simultaneously 

 from Peru to the Caribbean Islands; but they do not affect 

 the Sierra Nevada. The occasional slight tremors recorded 

 are purely local. 



North of the Sierra the Caribbean coast extends nearly 

 east and west; but at Cabo de Aguja, near Santa Marta, it 

 turns southward at a right angle ; twenty miles from the point 

 the high coast touches the plain about the great lagoon called 

 La Cienega; beyond this the mountainous lands adjoin the 

 plain along the north and south line. The plain and lagoon 

 are part of the estuary system of the Magdalena. 



Our explorations were made mainly within a triangle 

 formed by the coast and the San Lorenzo Mountains. These 

 mountains form a lower chain, trending from west-south- 

 west to east-northeast, and are separated from the Sierra 

 Nevada by a narrow and deep valley; the Horqueta, one of 

 their peaks, is 8400 feet high as measured by my aneroid, 

 and I judge that the San Lorenzo Mountains, which I did not 

 reach, are at least 500 feet higher. To the northwest of the 

 principal range are several lower ridges, roughly parallel to 

 it and abutting diagonally on the northern coast. This por- 

 tion of the coast is remarkably picturesque, a succession of 

 rocky headlands with deep bays between the ridges ; the bays 

 are often backed by sand beaches and mangrove swamps of 

 no great extent. Further east the headlands are no longer 

 seen, and low, rolling lands extend back to the base of the 

 Sierra Nevada. 



Numerous streams rise in the San Lorenzo Mountains, 

 flowing down through deep ravines in long series of cascades ; 

 as they approach the coast they have wide valleys with more 

 or less alluvial land. The most important of these streams 



