CHAP. VII THE GLACIAL EPOCH 119 



Further evidence of this alternation is found both in the 

 Isle of Man and in Ireland, where two distinct boulder 

 clays have been described with intervening beds of gravels 

 and sands. 



Palceontological Evidence of Alternate Cold and Warm 

 Periods, — Especially suggestive of a period warmer than 

 the present, immediately following glacial conditions, is 

 the occurrence of the hippopotamus in caves, brick-earths, 

 and gravels of palaeolithic age. Entire skeletons of this 

 animal have been found at Leeds in a bed of dark blue 

 clay overlaid by gravel. Further north at Kirkdale cave, 

 in N. Lat. 54° 15', remains of the hippopotamus occur abun- 

 dantly along with those of the Elephas antiquus, Rhino- 

 ceros heviitcechus, reindeer, bear, horse, and other quadru- 

 peds, and with countless remains of the hyaenas which 

 devoured them ; while it has also been found in cave de- 

 posits in Glamorganshire, at Durdham Down near Bristol, 

 and in the post-Pliocene drifts of England and France. 



The fact of the hippopotamus having lived at 54° N. Lat. 

 in England immediately after the glacial period seems 

 quite inconsistent with a mere gradual amelioration of 

 climate from that time till the present day. The entirely 

 tropical distribution of the existing animal and the large 

 quantity of vegetable food which it requires both indicate 

 a much warmer climate than now prevails in any part of 

 Europe. The problem, however, is complicated by the fact 

 that, both in the cave-deposits and river gravels, its remains 

 are often found associated with those of animals that 

 imply a cold climate, such as the reindeer; the mammoth, 

 or the woolly rhinoceros. At this time the British Isles 

 were joined to the Continent, and a great river formed by 

 the union of the Rhine, the Elbe and all the eastern rivers 

 of England, flowed northward through what is now the 

 German Ocean. The hippopotamus appears to have been 

 abundant in Central Europe before the glacial epoch, but 

 during the height of the cold was probably driven to the 

 south of France, whence it may have returned by way of 

 the Rhone valley, some of the tributaries of that river 

 approaching those of the Rhine within a mile or two a 

 little south-west of Mulhausen, whence it would easily 



