THE study of islands, whether the attention of the visitor is directed to their structure or their inhabitants, yields a peculiar pleasure. They are quite definite and unique units. They reveal interesting relations with neighboring continents, of which they so often are merely separated fragments, and they afford texts for suggestive and fascinating speculations as to past geographical conditions.
In their life no less than in their mineral features, they exhibit to the naturalist, familiar with the interpretation of forms, biological affinities with distant or near-by lands, and thereby shed side-lights, frequently instructive, upon the migrations of plants and animals. And they are, or have been, in themselves experimental stations, where the theories of specific change or specific origin may find partial endorsement or helpful refutation.
Long before Wallace wrote his "Island Life," they had attracted observers, and the unity with, or the diversity from, adjoining islands or contiguous mainlands, of their flora and fauna furnished abundant proofs of their ancient separation or their recent union with both.
An island, too, has its limits so irrevocably fixed, becomes, from its isolation, such a definite tract, that its study has the economical value of concentration and persistency. And this advantage obviously reaches phenomenal value, the more remote the island is from any other, because then its peculiarities teach the naturalist lessons in the origin of living species, or supply the geologist with new types of terrestrial architecture.
It was long ago pointed out that