48 THE WANDERINGS OF ANIMALS [OH. 



3. Cool temperate belt, frequently coinciding 

 with the normal cloud-belt. Those trees which are 

 deciduous lose their leaves during the winter season, 

 which is well marked. The upper limit of this belt 

 coincides with the 'upper tree line.' 



4. Cold belt. Characterised by grassy slopes 

 wjth abundance of flowering annuals. Higher up 

 the grass gives way to mosses and lichens. 



5. Arctic belt, the lower limit of which is near 

 the permanent snow-line, which within the tropics is 

 somewhere near 15,000 feet elevation. 



Now, since an isolated mountain is like a cone, 

 it is of the greatest significance that its successive 

 vertical zones, if projected in Mercator's fashion, are 

 practically repeated in a grander scale by the zones 

 on a map of the northern half of the world. We 

 may compare the mountain cone with the northern 

 hemisphere of a globe. The agreement is somewhat 

 distorted by the configuration of the continents, by 

 the high elevation of Central Asia and by the in- 

 troduction of deserts. There are in the northern 

 hemisphere : 



1. A tropical belt, either moist, with tropical 

 forests, as in Central and South America, parts of 

 Africa, Indo-Malaya and Papuasia ; or dry, ' torrid,' 

 like the Sahara and Arabia. 



2. A warm temperate belt, sub-tropical. 



3. A cool temperate belt, with much woodland 



