n] FEATURES OF ENVIRONMENT 51 



mountains, whilst the other side slopes rapidly down 

 into the hot lands. 



The component species of the faunas and floras of 

 such mountain zones can be collected and studied as 

 to their affinities and variations. Some creatures 

 seem to be quite indifferent to climate, and there- 

 fore have a long vertical and horizontal range. The 

 puma, for instance, ranges from Canada to Patagonia ; 

 it makes raids into the hot lands and ascends to the 

 upper tree-line. The nine-banded armadillo is equally 

 at home in the moist hot lands and in the clammy 

 pine forests of 9000 feet elevation in Mexico. A 

 certain kind of small lizard, Sceloporus microlepidotm, 

 of the same country occurs in the lowlands and 

 ascends to the very tree-line where it is obliged to 

 hibernate through perhaps half the year, whilst below 

 it aestivates during the torrid season. Other species, 

 although scattered widely over the country, have a 

 very short vertical range, so strictly limited that these 

 animals and plants indicate the elevation above sea- 

 level as safely as a barometer. Ultimately most 

 animals are dependent upon the vegetation, the state 

 of which depends greatly upon climate and soil. The 

 jaguar lives on herbivorous game. Rattlesnakes sub- 

 sist mainly upon rodents, and mice ascend as far as 

 there are roots and seeds for them to eat. Where the 

 winter time is severe many animals have either to 

 migrate into lower, warmer climes, or they are forced 



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