100 



the western to the eastern parts of the old continent ; but the 

 quadrupeds which inhabit the temperate climate of America are 

 peculiar races. The equatorial region contains three extensive 

 tracts widely separated from each other by sea : each of the 

 three tracts has a distinct nation of quadrupeds. The large re- 

 gion of Australia forms another zoological province, in which 

 are contained many indigenous tribes of a very singular descrip- 

 tion ; and lastly, the southern extremities of America and Africa 

 are each distinguished by the possession of peculiar races, 



Of these several provinces into which the animal world admits 

 of division, none has so remarkable a stock of animals as Australia. 

 It possesses several entire genera of quadrupeds which have been 

 discovered in no other part of the world. One remarkable tribe 

 is the Marsupial, which term comprises such as produce their 

 young in an immature state, and keep them for a time attached 

 to their bodies, chiefly in abdominal bags, given them by nature 

 for that purpose. The opossum is peculiar to the southern hemi- 

 sphere, and is very common in the lofty forests of America. 

 We behold in every region striking instances of the structure 

 of animals being fitted to the general nature of the country 

 in which they reside. 



If we take a general view of the zones of equal temperature, 

 both above and below the level of the sea, and consider that each 

 has its peculiar vegetation, and again, that each zone is furnished 

 with different groups of animals adapted to its temperature and 

 general production, we can easily conceive that a very slight 

 oscillation of land and sea would cause the extinction of whole 

 genera of animals and plants, and that those bands of variable 

 temperature, from the equator to the poles, can never be ex- 

 pected to be parallel to the equator, but always to present great 

 undulations according to the relative position and height of the 

 dry land and the bottom of the sea. Therefore, in tracing the 

 general effects of the northerly movement of the surfaces, and 

 comparing the effects with existing nature, we must take all the 

 above questions on the modifying causes of temperature and 

 variable distribution of vegetables and animals into conside- 

 ration, and not be limited to the mathematical zones of geo- 

 graphy. 



In closing this chapter, we may note, that various calculations 



