CHAP. 1.] 



INTEODUCTORY. 



U 



accurate conception of the physical and organic changes which 

 have resulted in the present state of the eaith. 



The indications now given of the scope and purpose of the 

 present volume renders it evident that, before we can proceed 

 to the discussion of the remarkable phenomena presented by 

 insular faunas and floras, and the complex causes which have 

 produced them, we must go through a series of preliminary 

 studies, adapted to give us a command of the more important 

 facts and principles on which the solution of such problems 

 depends. The succeeding eight chapters will therefore be 

 devoted to the explanation of the mode of distribution, variation, 

 modification, and dispersal, of species and groups, illustrated by 

 facts and examples; of the true nature of geological change 

 as affecting continents and islands ; of changes of climate, their 

 nature, causes, and effects ; of the duration of geological time 

 and the rate of organic development. 



