CH. Ill 



LOCALITY 45 



variations of types of forest at various elevations can be 

 noted. In Mexico the basal region extends to about 

 1000 metres (3000 ft.), and consists of tropical rain- 

 forest to the south, while farther north the moist 

 ravines alone have this type of forest. On the spurs is 

 an open thorn-forest of Cactaceae, Acacias, aud Tree- 

 lilies. From 1000 to 2000 metres (3000 to 6000 ft.) 

 the montane region has a heavy rain-forest consisting 

 largely of evergreen oaks in the lower portion, and 

 deciduous oaks higher up. Above 2000 metres the 

 coniferous forest begins, and this belt, in the higher parts, 

 gradually gives way to scattered deciduous oaks, limes, 

 and alders. The upper parts of the elevated peaks of 

 Orizaba and Popocatepetl are covered by steppe and 

 shrub, and finally end in desert. 



The mountain regions of equatorial South America, 

 in Ecuador, New Grenada, and Venezuela, show similar 

 gradation from the rain-forest in the basal and montane 

 belts and dwarf trees passing into steppe, here called 

 paramos. The temperate belt is characterised by being 

 the home of most Cinchonas. Farther south, the rain- 

 fall on the western slopes being scanty, these have the 

 appearance of deserts, and have only a very scanty vege- 

 tation. Such an alpine desert is called a puna. As 

 regards the littoral mountain ranges of Brazil, which do 

 not rise above 2700 metres (ab. 8900 ft.), the basal 

 tropical forest is followed by the montane zone, in which 

 the twiners are few and thin and epiphytes scarce ; and 

 in the upper portions of this belt will often be found 

 a pure forest of Araucaria hraziliana, above which 

 there is a similar formation to the carapos described 

 before. 



We have already seen in foregoing descriptions of 

 forests that their character in the vicinity of the sea or 

 other sheets ofivater, or in damp ravines, is affected not 

 only by the saturation or infiltration of water into the soil, 

 but by the greater relative humidity of the atmosphere ; 

 and that, where the latter is great, the forests are generally 

 evergreen, as, for example, over the greater part of the 



