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 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 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 when 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. 
