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Show 100 ISLAND LIFE. developed, which, '''hen again brought into competition with the fauna from which they had been separated, ·would cause fresh struggles of ever increasing complexity, and thus lead to the development and preservation of every weapon, every habit, and every instinct, which could in any way conduce to the safety and preservation of the several species. Changed Dist1·ibution prroved by the Extinct Animals of D{(ferent epochs.-We thus find that, while the inorganic world has been in a state of continual though very gradual change, the species of the organic world have also been slowly changing in form and in the localities they inhabit; and the records of these changes and these migrations are everywhere to be found, in the actual distribution of tbe species no less than in the fossil remains which are preserved in the rocks. Everywhere the animn.ls which have most recently become extinct resemble more or less closely those which now live in the same country; and where there are exceptions to the rule, we can generally trace them to some changed conditions which have led to the extinction of certain types. But when we go a little further back, to the late or middle Tertiary deposits, we almost always find, alo:n.g with forms which might have been the ancestors of some now living, others which are only· now found in remote regions and often in distinct continents-clear indications of those extensive migrations which have ever been going on. Every large island contains in its animal inhabitants a record of the period when it was last separated from the adjacent continent, while some portions of existing continents still show by the comparative poverty and speciality of their animals that .at no distant epoch they were cut off by arms of the sea and formed islands. If the geological record were more perfect, or even if we ha.d a::> good a knowledge of that record in all parts of the world as we have in Europe and North America, we could arrive at much more accurate results than we are able to do with our present very imperfect knowledge of extinct forms of life; but even with our present scanty information we are able to throw much light upon the past history of our globe and its inhabitants, and can sketch out with confidence many of the changes they must have undergone. cuAr. VI.] GEOGHAPHICAL AND GEOLOGICAL CHANGES. 101 Summ,ary of Evidence jo1· the Gcne1·al Permanence of Continents and Oceans.-As this question of Lhe permanence of our continents lies at the root of all our inquiries into the past changes of the earth and its inhabitants, and as it is at present completely ignored by many writers, and even by naturalists of eminence, it wiJl be well to summarise the various kinds of evidence which go to establish it.1 We know as a fact that all sedimentary deposits have been formed under water, but we also know that they were largely formed in lakes or inland seas, or ncar the coasts of continents or great islands, and that deposits uniform in character and more than 150 or 200 miles wide were rarely, if ever, formed at the same time. The further we go from the land the loss rapidly deposition takes place, hence the great bulk of aU the strata must have been formed near l~nd. Some deposits are, it is true, continually forming in ~he m1dst of the great oceans, but these are chiefly organic ancl mcrease very slowly, and there is no proof that any part of the series of known geological formations exactly resembles them. Chalk, which is still believed to be such a deposit by many naturalists, has been shown, by its contained fossils, to be a . 1 In a review of Mr. Reade's Chemical Denudation and Geological Time m Natw·e (Oct. 2nd, 1879) the writer remarks as follows: - " 011e of the funny notions of some scientific thinkers meets with no favour from Mr. Reac~e, whose geological knowledge is practical as well as theoretical. They consider that because the older rocks contain nothing like tho present red clays, &c., of the ocean floor, that the oceans have always been in their present positions. Mr. Reade points out that the first proposition is not yet proved, and tlte distribution of animals and plants and the fact that the ~u!~< of the strata on l~nd are of marine origin are opposed to tho hypothesis. We must leave 1t to our readers to decide whether the "notion" developed in this chapter is "funny," or whether such hasty and superficial arguments as those l1ere quoted from a 11 practical geologist" have any value as against the different classes of facts, all pointing to an opposite conclusion, wltich have now been briefly laid before them, supported as they are by the expressed opinion of so weighty an authority as Professor Archibald Geikie, who, in tho lectnre already quoted says :- '1 From all this evidence we may legitimately conclude that the present land of tho globe, though formed in great measure of marine formations has never lain under tho deep sea ; but that its site must always havo 1 been ncar Janel. Even its thick marino limestones arc the deposits of comparatively shallow water." |