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now anywhere to be found which could conduct us back through a series of "links" to the (log's wild ancestors? And if we set the problem some hundreds of thousands of years (not to say millions) into the future, for the paleontologists of those days to solve, does their work become any easier than it would be for us if performed at present?

Wherever the known incompleteness of the geological record' is insufficient to account for a difficulty, it becomes the believer in the development theory frankly to acknowledge that the riidle is too intricate to be solved by any means at his command. And yet, until an evolutionary rise of species had been assigned as an explanation of the succession of higher and higher animals and plants throughout the geological ages, what adequate reason for this progress of life could be given? Strike out from our present conception of the organic world, class after class, all notion of actual relationslip ly descent, and what have we left but in mighty list of extinct creatures whose rise, progress, and disappearance are far more unaccountable than that of the genii of the Arabian Nights!

I Darwin's Origin of Species, chap. ix.; Dana's Manual of Geology, pp. 600, 601; Nicholson's Aucicat Life-History of the Earth, pp. 50, 51.

CHAPTER VIII.

THE TESTIMONY OF GEOGRAPHICAL DISTRI

BUTION.

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HEN an Englishman travels by the nearest sea

route from Great Britain to Northern Japan, he passes by countries very unlike his own, both in aspect and natural productions. The sunny isles of the Mediterranean, the sands and date-palms of Egypt, the arid rocks of Aden, the cocoa-groves of Ceylon, the tiger-haunted jungles of Malacca and Singapore, the fertile plains and volcanic peaks of Luzon, the forest-clad mountains of Formosa, and the bare hills of China, pass successively in review, till, after a circuitous voyage, of thirteen thousand miles, he finds himself at Hakodadi in Japan. He is now separated from his starting-point by the whole width of Europe and Northern Asia, by an almost endless succession of plains and mountains, arid deserts or icy plateaus; yet, when he visits the interior of the country, he sees so many familiar natural objects, that he can hardly help fancying he is close to his home. There are also, of course, many birds and insects which are quite new and peculiar; but these are by no means so numerous or conspicuous as to remove the impression of a wonderful resemblance between the productions of two such remote islands as Britain and Yesso. ... In the western hemisphere we find examples equally striking. The Eastern United States possess very peculiar and interesting plants and animals, the vegetation becoming more luxuriant as we go south, but not altering in essential character; so that, when we reach the southern extremity of Florida, we still find ourselves in the midst of oaks, sumachs, magnolias, vines, and other characteristic forms of the temperate flora; while the birds, insects, and landshells are almost identical with those found farther north. But if we now cross over the narrow strait, about fifty miles wide, which separates Florida from the Bahama Islands, we find ourselves in a totally different country, surrounded by a vegetation which is essentially tropical, and generally identical with that of Cuba. The change is most striking, because there is no difference of climate, of soil, or apparently of position, to account for it; and when we find that the birds, the insects, and especially the land-shells, are almost all West-Indian, while the North-American types of plants and animals have almost all completely disappeared, we shall be convinced that such differences and resemblances cannot be due to existing conditions, but must depend upon laws and causes to which mere proximity of position offers no clew.'

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In these suggestive sentences Mr. Wallace lays before the reader one of the most interesting problems which the naturalist has to consider, — namely, the relations between the fauna and flora of a region and its geographical position and other characters. The present chapter will try to point out the bearing which the teachings of zoological and botanical geography have upon the development theory. To do this, it will first be necessary to give an outline of the zoological regions into which the earth has been divided.

1 Wallace, Island Life, 17. :3-5. 2 Such as soil, cimate, geological history, and so on.

If we take an ordinary terrestrial globe, and study the arrangement of the great land-masses on its surface, we shall at once see that they are strung together in a very irregular way.

If a circle be drawn, with Behring Strait as a centre, so as to pass around the globe at a distance eighty degrees away from this centre, we shall find that the continental masses are either quite broken apart from each other, or (as in the case of the two Americas) are united, where this circle crosses them, by only a slender strip of land.

From the fact that the places where the continents are or have been separated from each other are indicated by the position of this circle which has just been described, it is called the zone of fracture. The only break between two continents, which does not lie somewhere along this circle, is the one at Behring Strait, its centre. A glance at the adjoining map 1 will make the whole matter plain.

i From Guyot's Physical Geography, p. 21.

It is clear enough, as the map shows, that the continents radiate away from Behring Strait as a centre. It is easy, too, to see that the circle

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marked “ Zone of Fracture corresponds to a real belt of separation between the continental land-masses.

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