100 



ISLAND LIFE. 



[part I. 



developed, which, when again brought into competition with 

 the fauna from which they had been separated, would cause 

 fresh struggles of ever increasing complexity, and thus lead to 

 the development and preservation of every weapon, every habit, 

 and every instinct, which could in any way conduce to the 

 safety and preservation of the several species. 



Changed Distribution proved hj the Extinct Animals of Different 

 epochs. — We thus find that, while the inorganic world has been 

 in a state of continual though very gradual change, the species 

 of the organic world have also been slowly changing in form and 

 in the localities they inhabit ; and the records of these changes 

 and these migrations are everywhere to be found, in thB 'actual 

 distribution of the species no less than in the fossil remains 

 which are preserved in the rocks. Everywhere the animals 

 which have most recently become extinct resemble more or less 

 closely those which now live in the same country ; and where 

 there are exceptions to the rule, we can generally trace them to 

 some changed conditions which have led to the extinction of 

 certain types. But w^hen we go a little further back, to the late 

 or middle Tertiary deposits, we almost always find, along with 

 forms which might have been the ancestors of some now living, 

 others which are only now found in remote regions and often in 

 distinct continents — clear indications of those extensive migra- 

 tions which have ever been going on. Every large island 

 contains in its animal inhabitants a record of the period when 

 it was last separated from the adjacent continent, while some 

 portions of existing continents still show by the comparative 

 poverty and speciality of their animals that at no distant epoch 

 they were cut off by arms of the sea and formed islands. If 

 the geological record were more perfect, or even if we had as 

 good a knowledge of that record in all parts of the world as we 

 have in Europe and North America, we could arrive at much 

 more accurate results than we are able to do with our present 

 very imperfect knowledge of extinct forms of life ; but even 

 with our present scanty information we are able to throw much 

 light upon the past history of our globe and its inhabitants, and 

 can sketch out with confidence many of the changes they must 

 have undergone. 



