VI PREFACE. 



rational to suppose that an explanation is to be 

 found, either in the condition of the earth's sur- 

 face, climate or change of the seasons, the 

 supply of food, or some other cause depending 

 on local peculiarities. 



It is by these local Faunas that the Geogra- 

 phical distribution of animals has been of late 

 so successfully cultivated, and a few of the laws 

 which govern them ascertained. It has been 

 found that similar climates however widely 

 separated from each other, are inhabited by 

 similar animals, or animals of similar habits. 

 Thus it is that the Himalaya mountains of Asia, 

 which rise from the plains of the torrid zone 

 through every belt of climate, to regions of per- 

 petual snow, have representatives of almost 

 every living class of creatures. This is of course 

 considerably modified by the character of the 

 surrounding country. If the zones of climate 

 follow closely on each other, each becomes varie- 

 gated by the encroachments of the productions 

 of those above and below ; the nature also of 

 the soil considerably modifies it, such as hill 

 or plain or swamp. But there are phenomena 

 regarding the distriijution of animals which at 

 present seem inexplicable, such is the congre- 

 gation of peculiar classes of animals in particular 

 districts, beyond which they may almost l)e said 

 to be extinct, a remarkable instance of which 

 is to be found in the zoology of New South 

 Wales. 



