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to invade the country of the reindeer. All the remains of 
fossil hippopotamus in this country which I have seen, with 
two exceptions, belong to adults, and it is very probable that 
that animal seldom or never bred in our country. The mam- 
moth has purposely been omitted in this analysis of the evidence 
afforded by the mammalia as to the climate, because it happens 
to be one of the few creatures which were able to live under 
very different climatal conditions, being found alike in the 
volcanic ash in which Rome is built, the frozen marshes of 
Siberia, and in the morasses of the Southern States. 
Nor does this evidence as to the Pleistocene climate stand 
alone. The contorted gravels, and the angular state of the 
pebbles of which they are often composed, are, as Mr. Prest- 
wich infers, explicable only on the theory of ice having been 
formed in our rivers in larger quantities than at the present 
day : the one being the result of the grounding of large masses 
of ice, and the other of their melting away, and consequently 
dropping their burden of pebbles. The large plateaux of brick 
earths are also probably deposited by floods, caused, like those 
of Siberia and North America, by the sudden melting of the 
winter snow. 
This consideration of a Pleistocene climate leads necessarily 
to the difficult problem of the relation of the Pleistocene 
mammalia to the period of intense cold, the Glacial period ; 
and before this can be discussed, I must define exactly what 
I mean by the term. At the close of the Pleiocene period the 
temperature of northern and central Europe became lowered 
to such a degree that it became almost Arctic in character, and 
those complex phenomena were manifested which we know as 
glacial. And the latter indicate geographical changes of 
enormous magnitude. The researches of many eminent ob- 
servers prove, that at the commencement of the Glacial period 
an enormous sheet of ice, like that under which Greenland now 
lies buried, extended from the hills of Scandinavia over North 
Germany, the North Sea, Scotland, Ireland, Cumbria, and the 
hilly districts of England, at least as far south as the valley of 
the Thames. The land then, most probably, as Professor 
Ramsay and Sir Charles Lyell believe, stood higher than it 
does now. Then to this succeeded a period of depression, 
during which the mountains of Wales were submerged to a 
height of at least 1,300 ft. ; and the waves of the sea washed 
out of the pre-existing glacier detritus the shingle and sand, 
termed the 4 middle drift,’ of the North of England and of Scot- 
land and Ireland.* Then the land was re-elevated above the 
* I have to acknowledge the kind assistance of Professor Hull, F.R.S., 
Mr. Kinahan, and the Rev. M. H. Close, in this portion of the subject. 
