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Show 310 ISLAND L[FE. (PART II. Concluding Observations on the Fauna and Flora of the Sandwich Islands.-The indications thus afforded by a study of the flora seem to accord well with what we know of the fauna of the islands. Plants having so much greater facilities for dispersal than animals, and also having greater specific longevity and greater powers of endurance under adverse conditions, exhibit in a considerable degree the influence of the primitive state of the islands and their surroundings; while members of the animal world, passing across the sea with greater difficulty and subject to extermination by a variety of adverse conditions, retain much more of the impress of a recent state of things, with perhaps here and there an indication of that ancient approach to America so clearly shown in the Compositre and some other portions of the flora. ,GeneTal Rernarlcs on Oceanic Islands.-We have now reviewed the main features presented by the assemblages of organic forms which characterise the more important and best known of the Oceanic Islands. They all agree in the total absence of indigenous mammalia and amphibia, whiie their reptiles, when they possess any, do not exhibit indications of extreme isolation and / antiquity. Their birds and insects present just that a.mount of specialisation and diversity from continental forms which may be best explained by the known means of dispersal acting through long periods ; their land shells indicate greater isolation, owing to their admittedly less effective means of conveyance across the ocean; while their plants show most clearly the effects of those changes of conditions which we have reason to believe have occurred during the Tertiary epoch, and preserve to us in highly specialised and archaic forms some record of the primeval immigration by which the islands were originally clothed with vegetation. But in every case the series of forms of life in these islands is scanty and imperfect as compared with far less favourable continental areas, and no one of them presents such an assemblage of animals or plants as we always find in an island which we know has once formed part of a continent. 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 ·~ CIIAP. XV.] OCEANIC ISLANDS. 311 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 and submerged volcanic islands), 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. |