94 Annals of the Carnegie Museum. 



evolutionary changes in the forms which had succeeded in reaching 

 the western extremity of the chain, through the operation of influences 

 due to isolatioti. 



This theory of the origin of the Subtropical of the Sierra Nevada 

 seems to sufficiently account for all the facts in the case: the im- 

 poverished fauna; the occurrence of several highly peculiar, isolated 

 forms; the resemblance of the fauna as a whole to that of the Ven- 

 ezuelan Andes ; and the dissimilarity between it and the corresponding 

 fauna of the Eastern Andes. It is supported by such geological evi- 

 dence as we have (compare Sievers, Zeitschrift der Gesellschaft fur 

 Erdkunde su Berlin, XXIII, 1888, 67, and Petermanns Mitteilungen, 

 XLII, 1896, 128). There is another bit of collateral evidence which 

 also has considerable interest and significance in this connection, 

 and may be referred to briefly. It is known that Brachyspisa capensis 

 peruviana is properly a form of the Temperate Zone, but that it is one 

 of the few forms of that zone which is capable of existing at lower 

 altitudes. We find it on the island of Curaqao at sea-level, under a 

 sightly different phase (insularis) , the lone survivor of a once ex- 

 tensive Subtropical and Temperate fauna which must have inhabited 

 this part when it stood perhaps as high as the Sierra Nevada does now. 



The Temperate Zone. 



Character and Extent. — The Temperate Zone is poorly represented 

 in the Sierra Nevada de Santa Marta, both in characteristic vegetation 

 and in bird-life. This is of course due in part to the restriction of the 

 area falling within its limits here,^^ which naturally operates to restrict 

 the diversity of its life. Its lower boundary may be set at about 

 8,500 or 9,000 feet, mainly on the ground that this elevation constitutes 

 the upper limit for a considerable number of Subtropical Zone forms, 

 but many species which in the Andes are coflfined to the Temperate 

 Zone forests are present here as low down as 5,000 feet, -and thus 

 enter the lower zone, at least on the north slope of the Nevada. 

 There are no heavy forests in the region under discussion at th6 alti- 

 tudes at which the Temperate Zone forests of the Andes lie, such 



18 The Temperate Zone as laid down on the map is surely out of proportion, 

 but its true limits are practically unknown except in the San Lorenzo region 

 and the Macotama Valley, and due allowance must be made for the insuffi- 

 ciency of the base-map. 



