CHAP. YIl.] 



THE GLACIAL P^POCH. 



115 



pachyderms, and of such a littoral Lusitanian fauna as that of 

 the Selsea bed where it is mixed up with the remains of some 

 of those pachyderms, as well as of some other features, it has 

 seemed to me that the climate of the earlier part of the post- 

 glacial period in England was possibly even warmer than our 

 present climate ; and that it was succeeded by a refrigeration 

 sufficiently severe to cause ice to form all round our coasts, and 

 glaciers to accumulate in the valleys of the mountain districts ; 

 and that this increased severity of climate was preceded, and 

 partially accompanied, by a limited submergence, which no- 

 where apparently exceeded 300 feet, and reached that amount 

 only in the northern counties of England."^ This decided 

 admission of an alternation of warm and cold climates since the 

 height of the glacial epoch by so cautious a geologist as Mr. 

 Wood is very important, as is his statement of an accompanying 

 depression of the land, accompanying the increased cold, because 

 many geologists maintain that a greater elevation of the land is 

 the true and sufficient explanation of glacial periods. 



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, im- 

 mediately 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 abundantly along with those of the ox, elephant, horse, 

 and other quadrupeds, and with countless remains of the 

 hysenas which devoured them ; while it has also been found 

 in cave deposits in Glamorganshire, at Durdham Down, near 

 Bristol, and in the post-Pliocene drifts of Dorsetshire. It is im- 

 portant to note that where it is associated with other mammals 

 in eaves — which are hyaena-dens, and not mere receptacles of 

 water-carried remains— these always imply a mild climate, the 

 elephant and rhinoceros found with it being species character- 

 1 Geological Magazine, 1876, p. 396. 



I 2 



