24 
groovings and scratches on the rocks of our mountain districts, 
heaps of moraine rubbish in the valleys such as we see vow at the 
termination of the Swiss glaciers, and enormous deposits of ‘‘ drift 
clay’ colleeted by the ice in its travels and deposited as the 
glacier melted. 
All through Miocene and Pliocene times the temperature had 
been gradually lowering, as we see by the increasing prevalence of 
Arctic forms of life and the lessening numbers of such as are now 
found in warm seas. As the cold developed itself more and more 
southwards and at last produced the ice masses, so the animals and 
plants were gradually driven in the same direction until the rein- 
deer grazed on the plains in the south of France. Whenever the 
cold moderated, as it did more than once, animal life swung 
northwards, and the mammoth and hippopotamus were preyed 
upon by hyenas as far north as Yorkshire. From river gravels and 
from cave deposits all over our land we have extracted a rich 
harvest of animal remains, sometimes of curiously mixed families 
owing to the variability of climatic conditions. 
Sir C. Lyell, in his ‘* Antiquity of Man,” describes the following 
successive geographical states of the British and adjoining areas :— 
First, a continental period when the upheaving movement at the 
close of Pliocene times continued until the land stood at a much 
higher level than it does at present. ‘‘ Britain formed part of the 
mainland, and the bottom of the old Pliocene sea became the 
feeding grounds of the animals which have left their remains in 
the Forest Bed, and all over and around the Dogger Bank. Ireland 
must also have been united to Britain to allow of their finding their 
way so far to the west.” At the same time, and perhaps partly in 
consequence of this elevation the temperature was lowered, and 
the country was invaded by numerous species of mammals from 
the north and west of Asia, where of course the climate was still 
more extreme. At length it became too cold even for these; snow 
and ice covered all the higher portions, while huge glaciers radiated 
from Scotland, Cumberland, and Snowdon, the marks of which I 
just now mentioned. Probably we owe the Scandinavian portion 
of our flora to this time. 
Then set in a period of submergence ; the shore-line retreated, 
and the glaciers deposited the boulder clay as they melied, and 
portions of them drifted off as icebergs as far at least as the 
valley of the Thames. Arctic mammals came in, driven gradually 
southward, and the Scandinavian plants ‘‘ which occupied the 
lower grounds during the previous continental period may have 
obtained exclusive possession of the only lands not covered with 
perpetual snow.” (Ant. Man. p. 331). 
