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Show 170 ISLAND LIFE. (PART J. · and that rocks or an entire country there would be no morames, d . debris are very ra.rely seen on icebergs. But urmg ~very . h th . '11 be a southern limit to the glaciated alaCial epoc ere WI • 'll o h this limit the mountam-tops w1 area and everyw ere near . . ' b h . nd deposit on it great masses of debr~s; nse far a ove t e we a . . and as the ice-sheet spreads, and ag~m as It passes away, this moraine-forming area will successively occupy tho who~e B t even such an ice-clad country as Greenland IS country. u ' . now known to have protruding peaks and rocky masses whwh · · t mor"'I·nes on its surface· 1 <YIVe nse o cu , and, as rocks from Cumber-land and Ireland were carried by the ice:sheet ~o the ~sle of 1\~an, there must have been a very long penod dunng whwh the Icesheets of Britain and Ireland terminated in the ocean .and sent off abundance of rock-laden bergs into the surroundmg seas; and the same thing must have occurred along all the coasts of Northern Europe and Eastern America. We cannot therefore doubt that throughout the greater part of the duration of a glacial epoch the seas arljacent to tho glaciated countries would receive continual deposits of largo rocks, rock-fragments, and gravel, similar to tho ~aterial of modern and ancient moraines, and analogous to the dnft and the numerous travelled blocks which the ice has undoubtedly scattered broadcast over every glaciated country; and these rocks and boulders would be imbedded in whatever deposits were then forming, either from the matter carried down by rivers or from the mud around off the rocks and carried out to sea by tlte 0 glaciers themselves. Moreover, as icebergs float far beyond the limits of the countries which gave them birth, these ice-borne materials would be largely imbedded in deposits forming from the denudation of countries which had never been glaciated, or from which the ice had already disappeared. But if every period of high excentricity produced a glacial epoch of greater or less extent and severity, then, on account of the frequent occurrence of a high _phase of excentricity during the three million years for which we have the tables, these boulder and rock-strewn deposits would be both numerous and extensive. Four hundred thousand years ago the excontricity 1 Nature, Vol. XXI., p. 345, " The Interior of G rcenland." CHAP. IX.) ANCIENT GLACIAL EPOCHS. 171 was almost exactly the same as it is now, and it continually increased from that time up to the glacial epoch. Now if we take double th.e ~resent excontricity as being sufficient to produce some .glaCiatiOn in the temperate zone, we find (by drawing out tho diagram at p. 165 on a larcrer scale) that durina 1 150 000 0 0 ' ' year.s out of the 2,400,000 years immediately preceding tho last glacial epoch, the excentricity reached or exceeded this amount con~isting of. sixteen separate epochs, divided from each other b; penods varymg from 30,000 to 200,000 years. But if the last glacial epoch was at its maximum 200,000 years ago, n. space of three million years will certainly include much, if not all, of the Tertiary period; and even if it does not, we have no reason to suppose that the character of the excentricity would suddenly chango beyond the throe million years. It follows, therefore, that if periods of high excentricity, like that which appears to have been synchronous with our last glacial epoch and is generally admitted to have been one of its efficient causes, always produced glacial epochs (with or without alternating warm periods), then the whole of the Tertiary deposits in the north temperate and Arctic zones should exhibit constantly alternating boulder and rock-bearing beds, or coarse rock-strewn gravels analogous to our existing glacial drift, and with some corresponding change of organic remains. Let us then see what evidence can be adduced of the existence of such deposits, and whether it is adequate to support the theory of repeated glacial epochs during the Tertiary period. Evidences of Ice-action during the Tertiary Period.- The Tertiary fossils bo.th of Europe and North America indicate throughout warm or temperate climates, except those of the more recent Pliocene deposits which merge into the earlier glacial beds. The Miocene deposits of Central and Southern Europe, for example, contain marine shells of some genera now only found farther south, while the fossil plants often resemble those of Madeira and tho southern states of North America. Large reptiles, too, abounded, and man-like apes lived in the south of France and in Germany. Yet in Northern Italy, near Turin, there are beds of sandstone and conglomerate full of characteristic Miocene shells, but containing in an intercalated deposit |