The geographical distribution of animals, with a study of the relations ...

290 ZOOLOGICAL GEOGRAPHY. [part in.carnivora had reached it; and we consequently find there, nowholly terrestrial form of bird but the gigantic and powerfulJEpijomis, well able to defend itself against such enemies. Asalready intimated, we refer the South American element inMadagascar, not to any special connection of the two countriesindependently of Africa, but to the preservation there of anumber of forms, some derived from America through Africa,others of once almost cosmopolitan range, but which, owing to theseverer competition, have become extinct on the African continent,while they have continued to exist under modifiedformsin the two other countries.The depths of all the great oceans are now known to be soprofound, that we cannot conceive the elevation of their bedsabove the surfacewithout some corresponding depression elsewhere.And if, as is probable, these opposite motions of theearth's crust usually take place in parallel bands, and are tosome extent dependent on each other, an elevation of the seabed could hardly fail to lead to thesubmergence of large tractsof existing continents ; and this is the more likely to occur onaccount of the great disproportion that we have seen existsbetween the mean height of the land and the mean depth of theocean. Keeping this principle in view, we may, with someprobability, suggest the successive stages by which the Ethiopianregion assumed its present form, and acquired the strikingpeculiarities that characterise its several sub-regions. Duringthe early period, when the rich and varied temperate flora of theCape, and its hardly less peculiar forms of insects and of low typemammalia, were in process of development in an extensivesouth temperate land, we may be pretty sure thatthe east and much of the north of Africa was deep sea.the whole ofAt alater period, when this continent sank towards the south andeast, the elevation may have occurred which connected Madagascarwith Ceylon ; and only at a still later epoch, when theIndian Ocean had again been formed, did central, eastern, andnorthern Africa gradually rise above the ocean, and effect aconnection with the great northern continent by way of Abyssiniaand Arabia. And if this last change took place with