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Prestwich, in his admirable Memoirs on the eocene deposits of England and France, is able to draw a close general parallelism between the successive stages in the two countries; but when he compares certain stages in England with those in France, although he finds in both a curious accordance in the numbers of the species belonging to the same genera, yet the species themselves differ in a manner very difficult to account for, considering the proximity of the two areas, unless, indeed, it be assumed that an isthmus separated two seas inhabited by distinct, but contemporaneous, faunas.
As to the exhibits proper within the museum, it may be stated in a word that they cover the entire range of the faunas and floras of the globe in a variety and abundance of specimens that are hardly excelled anywhere, and only duplicated by one or two other collections in Europe and two or three in America.
Thus: Animals and plants began their existence together, not long after the commencement of the deposition of the sedimentary rocks; and then succeeded one another, in such a manner, that totally distinct faunas and floræ occupied the whole surface of the earth, one after the other, and during distinct epochs of time.
But each fauna is not necessarily exactly intermediate, as unequal intervals of time have elapsed between consecutive formations. It is no real objection to the truth of the statement, that the fauna of each period as a whole is nearly intermediate in character between the preceding and succeeding faunas, that certain genera offer exceptions to the rule.
Darwin relies upon indirect proofs, the bearing of which is real and incontestable"; who concedes that "his theory accords very well with the great facts of comparative anatomy and zoölogy, comes in admirably to explain unity of composition of organisms, also to explain rudimentary and representative organs, and the natural series of genera and species, equally corresponds with many palaeontological data, agrees well with the specific resemblances which exist between two successive faunas, with the parallelism which is sometimes observed between the series of palaeontological succession and of embryonal development," etc.; and finally, although he does not accept the theory in these results, he allows that "it appears to offer the best means of explaining the manner in which organized beings were produced in epochs anterior to our own."
Windsor Earl has made some striking observations on this head in regard to the great Malay Archipelago, which is traversed near Celebes by a space of deep ocean; and this space separates two widely distinct mammalian faunas. On either side the islands are situated on moderately deep submarine banks, and they are inhabited by closely allied or identical quadrupeds.
Of Faunas, the Arctic differs from the Temperate; the Temperate from the Tropical; and the South Temperate from the North Temperate. Nay, in the South Temperate Zone itself, the two regions of South Africa and South America are unlike in their mammals, birds, reptiles, fishes, mollusks, insects.
Along the whole west coast, which is inhabited by a peculiar marine fauna, tertiary beds are so scantily developed, that no record of several successive and peculiar marine faunas will probably be preserved to a distant age.
So that here three marine faunas range far northward and southward, in parallel lines not far from each other, under corresponding climates; but from being separated from each other by impassable barriers, either of land or open sea, they are wholly distinct.
Turning to the sea, we find the same law. No two marine faunas are more distinct, with hardly a fish, shell, or crab in common, than those of the eastern and western shores of South and Central America; yet these great faunas are separated only by the narrow, but impassable, isthmus of Panama.
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