It is still more important to note that none of these oceanic archipelagoes present us with a single type which we may suppose to have been preserved from Mesozoic times; and this fact, taken in connection with the volcanic or coralline origin of all of them, powerfully enforces the conclusion at which we have arrived in the earlier portion of this volume, that during the whole period of geologic time as indicated by the fossiliferous rocks, our continents and oceans have, speaking broadly, been permanent features of our earth's surface. For had it been otherwise--had sea and land changed place repeatedly as was once supposed--had our deepest oceans been the seat of great continents while the site of our present continents was occupied by an oceanic abyss--is it possible to imagine that no fragments of such continents would remain in the present oceans, bringing down to us some of their ancient forms of life preserved with but little change? The correlative facts, that the islands of our great oceans are all volcanic (or coralline built probably upon degraded volcanic islands or extinct submarine volcanoes), and that their productions are all more or less clearly related to the existing inhabitants of the nearest continents, are hardly consistent with any other theory than the permanence of our oceanic and continental areas. We may here refer to the one apparent exception, which, however, lends additional force to the argument. New Zealand is sometimes classed as an oceanic island, but it is not so really; and we shall discuss its peculiarities and probable origin further on. * * * * * {331} CHAPTER XVI CONTINENTAL ISLANDS OF RECENT ORIGIN: GREAT BRITAIN Characteristic Features of Recent Continental Islands--Recent Physical Changes of the British Isles--Proofs of Former Elevation--Submerged Forests--Buried River Channels--Time of Last Union with the Continent--Why Britain is poor in Species--Peculiar British Birds--Freshwater Fishes--Cause of Great Speciality in Fishes--Peculiar British Insects--Lepidoptera Confined to the British Isles--Peculiarities of the Isle of Man--Lepidoptera--Coleoptera confined to the British Isles--Trichoptera Peculiar to the British Isles--Land and Freshwater Shells--Peculiarities of the British Flora--Peculiarities of the Irish Flora--Peculiar British Mosses and Hepaticae--Concluding Remarks on the Peculiarities of the British Fauna and Flora.