102 



ISLAND LIFE 



PAET I 



upraised coral reefs of inland seas. The mountains of one 

 period have disappeared by denudation or subsidence, 

 while the mountains of the succeeding period have been 

 rising from beneath the waves. The valleys, the ravines, 

 and the mountain peaks, have been carved out and filled 

 up again ; and all the vegetable forms which clothe the 

 earth and furnish food for the various classes of animals 

 have been completely changed again and again. 



JEffect of Continental Changes on the Distribution of Ani- 

 mals. — It is impossible to exaggerate, or even adequately 

 to conceive, the effect of these endless mutations on the 

 animal world. Slowly but surely the whole population of 

 living things must have been driven backward and forward 

 from east to west, or from north to south, from one side of 

 a continent or a hemisphere to the other. Owing to the 

 remarkable continuity of all the land masses, animals and 

 plants must have often been compelled to migrate into 

 other continents, where in the struggle for existence under 

 new conditions many would succumb ; while such as were 

 able to survive would constitute those wide-spread groups 

 whose distribution often puzzles us. Owing to the repeated 

 isolation of portions of continents for long periods, special 

 forms of life would have time to be 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 develop- 

 ment 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 by 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 the actual distribution of the 

 species no less than in the fossil remains which are pre- 

 served 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 



