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Show 174 ISLAND LIFE. [PART I. - . . · h ve been made of any extensive collectiOns of orgamc remams a. . £ t formation yet explored, and from nearly all Its honzons, or a .one h . th three countries nearly every honzon place or anot er m ese . . may be sal' d to h ave y1· e Ided c0 ssils of some kmd. These fossils, J' h th they be the remains of a flora such as that of however, w e er . . . Sh of a vertebrate fauna contammg the crocodile and eppey, or . . . f t . 1 11 a . h s is yielded by beds mdiCat1ve o terres na ~a~~ sue a . . dcon 1.t .I ons, or of a molluscan assemblage su.c h as IS present .I n marine or fluvio-marine beds of the formatiOn, are of unm1s-t k bl tropical or sub-tropical character throughout; and no aay · l' f 1'1 t h tever has appeared of the mterca atwn o a g acia race w a . · d' · f pen·o d , much less of successive interca. la.t iOnS In 10at1.v e o more than one period of 10,500 years' glaCiatiOn. Nor can It ?e urged that the glacial epochs of the Eocene in England w~re m~ervals of dry land, and so have left no evidence of. theu existence behind them, because a large part of the contmuous sequence of Eocene deposits in this country cons~sts of alternations ~f fluviatile, fluvio-marine, and purely manne strata; so that 1t seems impossible that during the accumulation of the Eocene formation in England a glacial period could have occurred without its evidences being abundantly apparent. The Oligocene of Northern Germany and Belgium, and the Miocene of those countries and of France, have also afforded a rich molluscan fauna, which, like that of the Eocene, bas as yet presented no indication of the intrusion of anything to interfere with its uniformly sub-tropical character." 1 This is sufficiently striking; but when we consider that this enormous series of deposits, many thousand feet in thicl,ness, consists wholly of alternations of clays, sands, marls, shales, or limestones, with a few beds of pebbles or conglomerate, not one of the whole series containing irregular blocks of foreign material, boulders, or gravel such as we have seen to be the essential characteristic of a glacial epoch ; and when we find that this very same general character pervades all the extensive Tertiary deposits of temperate North America, we shall, I think, be forced to the conclusion that no general glacial epochs could 1 Geological Magazine, 1876, p. 3\:!2. f'HAl'. IX.) MILD AHCTI ' CLIMATES. 175 have occurred d .· 1 . 1. . -- 1 . unng t 1e1r ormatwn. It must be renwmbered t 1at the " 1m per £e ct1· 0n of the geological record'' will not help us here ' because th· e sen·e s of T ert1. ary deposi. ts I.S unusually complete and we t . l ' mus suppose some destructive aO'ency to have se ected all the int 1 t d 1 · 0 erca a e g acial beds and to have so com-ple. t ely made• away WI' th th em t 11 at not a fragment remains, wlule preservmg all or almost all the interglacial beds· and to have acted thus capriciously, not in one limited area ~nly, but over the whole northern hemisphere, with the local exceptions on rthe flanks of. great ~ountain ranges already referred to. Temperate Gh~ates ~n the ATctic r-egions.-As we have just seen, the ge~log10al .evidence of the persistence of sub-tropical or warm climates m the north temperate zone during the greater part of the Tertiary period is almost irresistible, and we have ~ow to ~onsider the still more extraordinary series of observatiOns whwh demonstrate that this amelioration of climate extended into the Arctic zone, and into countries now almost wholly buried in snow and ice. These warm Arctic cEmates have b:e.n explain~d by Dr. Croll as due to periods of high excentn.CJty With wmter in pe1·ihelion, a theory which implies alter~at:ng epochs of glaciation far exceeding wha,t now prevails; and It .Is therefore necessary to examine the evidence pretty closely m order to see if this view is more tenable in the case of the north polar regions than we have found it to be in that of the north temperate zone. The most recent of these milder climates is perhaps indicated by the abundant remains of large mammalia-such as the ma~mnoth, woolly rhinoceros, bison and horse, in the icy alluvial plams of Northern Siberia, and especially in the Liakbov Islands in the same latitude as the North Cape of Asia. These rem.ains occur not in one or two spots only, as if collected by eddies at tho mouth of a river, but along the whole borders of the Arctic Ocean ; and it is generally admitted that the animals must have lived upon the adjacent plains, and that a considerably milder climate than now prevails could alone have enabled them to do so. At what period this occurred ·we do not know but one of the last intercalated mild periods of tho O'}aciai epoch itself seems to offer all tho necessary conditions. Again, |