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Show llfl ISLAND LIFE. (rAR'L' I. istic of temperate latitudes (Blephas antiquus and Rhinoceros Juymitet3ch?ts). But when it occurs in gravels or in water-borne cave-deposits it is sometimes associated with the mammoth, the woolly rhinoceros and the reindeer, animals which, as certainly, imply a cold or even arctic climate. This difference is intelligible if we consider that the hyrena which carried the bones of all these animals into the caves, is itself indicative of a mild eli mate, and that there is nothing to cause the remains of animals of successive epochs to be intermingled in such caves. In the gravels however it is very different. During the warm periods the rivers would be inhabited by hippopotami, and the adjacent plains by elephants and horses, and their remains would be occasionally imbedded in deposits formed during floods. But when the cold period came on and these had passed southward, the same river banks would be grazed by mammoths and reindeer whose remains would sometimes intermingle with those of the animals which preceded them. It is to be noted, also., that in many of these river-d eposits there are proofs of violent floods causing much re-arrangement of materials, so that the remains of the two periods would be thus still further intermingled.1 The fact of the hippopotamus having lived at 54° N. Lat. in England, quite close to the time of the glacial epoch, is absolutely inconsistent with a mere gradual amelioration of climate from that time till the present day. The immense quantity of vegetable food which this creature requires, implies a mild and uniform climate with hardly any severe wint~r ; and no theory that has yet been suggested renders this possible except that of alternate cold and warm periods during the glacial epoch itself. In order that the hippopotamus could have reached Yorkshire and retired again as the climate changed, we may suppose it to have been a permanent inhabitant of the lower Rhone, between which river and the Rhine there is an easy communication by means of the Doubs and the Ill, some of whose tributaries approach within a mile or two of each other about fifteen miles south-west of Mulhausen. Thence the passage would be easy 1 A. Tylor, on "Quaternary Gravels." Quarte1'ly Jountal of Geological Society of London, 1869, pp. 83.95 (woodcuts). CUAP. Vli.] THE GLACIAL EPOCH. 117 down the Rhine into the great river which then flowed up the bed of the North Sea., and thence up the Humber and Ouse into Yorkshire. By this route there would be only one watershed to cross, and this might probably have been marshy; but we may also suppose the animals to have ascended the Bristol Channel after passing round a long extent of French and English coast (which would then have consisted of vast plains stretching far beyond the Scilly Isles), in which case they would find an equally easy passage over a low watershed from the valley of the Avon to that of the Trent and Yorkshire Ouse. A consideration of the long and circuitous journey required on any hypothesis, will at once convince us that it could never have been made (as some have supposed) annually, during the short hot summer of the glacial period itself; whereas the interglacial warm periods lasting several thousand years would allow for the animals' gradual migration into all suitable river- · valleys. Thus, the very existence of the hippopotamus in Yorkshire as well as in the south of England, in close association with glacial conditions, must be held to be a strong corroborative argument in favour of the reality of an interglacial warm period. EvidencB of interglacial warm periods on the Continent and in North America.-Besides the e':'idence already adduced from our own islands, many similar facts have been noted in other countries. In Switzerland two glacial periods are distinctly recognised, between which was a warm period when vegetation was so luxuriant as to form beds of lignite sufficiently thick to be worked for coal. The plants found in these deposits are similar to those now inhabiting Switzerland-pines, oaks, birches, larch, etc., but numerous animal remains are also found ·showing that the country was then inhabited by an elephant (Elephas antiquus), a rhinoceros (Rhinoceros etruscus), the urus (Bos primigeni~ts), the red deer, (Cervus elephas) and the cavebear, ( Urs~~s spelceus); and there were also abundance of insects.1 In Sweden also there are two "tills," the lower one having been in places partly broken up and denuded before the upper 1 Heer's Primmval World of Switzerland. Vol. II., pp. 148-168. |
