Alteration of climate, isolation by geological changes, such as the submergence of continents and islands, and the competition of other species, are among the causes which have at all times operated towards its destruction; while, since the evolution of man, his agency, so far as we can judge by what we know of his later history, has been especially active in the same direction. The limited distribution of many species, even when not enforced by insular conditions, is remarkable, and, of course, highly favourable to their destruction. A multiplicity of examples are familiar to naturalists, and possibly not a few may have attracted the attention of the ordinary observer. For instance, it is probably generally known, that in our own island, the red grouse (which, by the way, is a species peculiar to Great Britain) is confined to certain moorlands, the ruffs and reeves to fen districts, and the nightingale,[38] chough, and other species to a few counties; while Ireland is devoid of almost all the species of reptiles common to Great Britain. In the former cases, the need of or predilection for certain foods probably determines the favourite locality, and there are few countries which would not furnish similar examples. In the latter, the explanation depends on biological conditions dating prior to the separation of Ireland from the main continent. Among birds, it might fairly be presumed that the power of flight would produce unlimited territorial expansion, but in many instances the reverse is found to be the case: a remarkable example being afforded by the island of Tasmania, a portion of which is called the unsettled waste lands, or Western Country. This district, which comprises about one-third of the island upon the western side, and is mainly composed of mountain chains of granites, quartzite, and mica schists, is entirely devoid of the numerous species of garrulous and gay-plumaged birds, such as the Mynah mocking-bird, white cockatoo, wattle bird, and Rosella parrot, though these abundantly enliven the eastern districts, which are fertilized by rich soils due to the presence of ranges of basalt, greenstone, and other trappean rocks. Another equally striking instance is given by my late father, Mr. J. Gould, in his work on the humming-birds. Of two species, inhabiting respectively the adjacent mountains of Pichincha and Chimborazo at certain elevations, each is strictly confined to its own mountain; and, if my memory serves me correctly, he mentions similar instances of species peculiar to different peaks of the Andes.