ii] FEATURES OF ENVIRONMENT 47 



Thus the western coasts of India, exposed to the 

 monsoon, have a much greater rainfall than the inland 

 districts on the other side of the coast range. In 

 Mexico the Pacific side is much drier than the very 

 wet Atlantic side, this difference being responsible 

 for remarkably different faunas and floras. 



The possible number of floral and faunal zones on 

 a mountain is greatest in the tropics, since its base 

 may be in the hot tropical lowlands and its top above 

 the permanent snow-line. A mountain of the same 

 height, but situated in the arctic region, may be 

 entirely within the snow-line. The width of the 

 zones (not of course their vertical thickness), and the 

 abruptness of the change from one to another are 

 proportional to the steepness of the slope. 



Every 'complete' mountain arising high within 

 the tropics shows the following five belts or zones. 



1. Tropical belt. Climate hot, according to cir- 

 cumstances either moist or dry, or both according 

 to seasons. Vegetation evergreen, but deciduous 

 when there is a pronounced dry season. The upper 

 limit of this zone may be put near 3000 feet above 

 the level of the sea. 



2. Warm temperate belt. The difference between 

 summer and winter begins to get marked, and there 

 may be cool nights. Vegetation chiefly evergreen, 

 and if the leaves are deciduous this is due to a pro- 

 longed dry season. 



