Mauritius and Bourbon are lofty volcanic islands, evidently of great antiquity. They are about 100 miles apart, and the sea between them is less than 1,000 fathoms deep, while on each side it sinks rapidly to depths of 2,400 and 2,600 fathoms. We have therefore no reason to believe that they have ever been connected with {435} Madagascar, and this view is strongly supported by the character of their indigenous fauna. Of this, however, we have not a very complete or accurate knowledge, for though both islands have long been occupied by Europeans, the study of their natural products was for a long time greatly neglected, and owing to the rapid spread of sugar cultivation, the virgin forests, and with them no doubt many native animals, have been almost wholly destroyed. There is, however, no good evidence of there ever having been any indigenous mammals or amphibia, though both are now found and are often recorded among the native animals.[109] The smaller and more remote island, Rodriguez, is also volcanic; but it has, besides a good deal of coralline rock, an indication of partial submergence helping to account for the poverty of its fauna and flora. It stands on a 100-fathom bank of considerable extent, but beyond this the {436} sea rapidly deepens to more than 2,000 fathoms, so that it is truly oceanic like its larger sister isles. _Birds._--The living birds of these islands are few in number and consist mainly of peculiar species of Mascarene types, together with two peculiar genera--Oxynotus belonging to the Campephagidae or caterpillar-catchers, a family abundant in the old-world tropics; and a dove, Trocazza, forming a peculiar sub-genus. The origin of these birds offers no difficulty, looking at the position of the islands and of the surrounding shoals and islets.