STEPPES AND DESERTS. 7 



in social community in subterranean caverns, and often fero- 

 ciously attack man, for whose defence their progenitors fought. 



Like the greater part of the desert of Sahara (16), the 

 Llanos, the most northern plains of South America, lie within 

 the torrid zone^ Twice in every year they change their 

 whole aspect, during one half of it appearing waste and bar- 

 ren like the Lybian desert; during the other, covered with 

 verdure, like many of the elevated Steppes of Central Asia (IV). 



The attempt to compare the natural characteristics of 

 remote regions, and to pourtray the results of this comparison 

 in brief outline, though a gratifying, is a somewhat difficult 

 branch of physical geography. 



A number of causes, many of them still but little under- 

 stood (18), dimmish the dryness and heat of the New World. 

 Among these are: the narrowness of this extensively in- 

 dented continent in the northern part of the tropics, where 

 the fluid basis on which the atmosphere rests, occasions 

 the ascent of a less warm current of air ; its wide extension 

 towards both the icy poles; a broad ocean swept by cool 

 tropical winds ; the flatness of the eastern shores ; currents 

 of cold sea- water from the antarctic region, which, at first 

 following a direction from south-west to north-east, strike 

 the coast of Chili below the parallel of 35 south lat., and 

 advance as far north on the coasts of Peru as Cape Parina, 

 where they suddenly diverge towards the west ; the numerous 

 mountains abounding in springs, whose snow-crowned sum- 

 mits soar above the strata of clouds, and cause the descent 

 of currents of air down their declivities ; the abundance of 

 rivers of enormous breadth, which after many windings in- 

 variably seek the most distant coast; Steppes, devoid of 

 sand, and therefore less readily acquiring heat ; impenetrable 

 forests, which, protecting the earth from the sun's rays, or 

 radiating heat from the surface of their leaves, cover the 

 richly- watered plains of the Equator, and exhale into the in- 

 terior of the country, most remote from mountains and the 



