CLIMATE OF POST-PLIOCENE PERIOD. 
161 
Climate of the Post-pliocene Period. —The evidence as to 
the climate of Europe during this epoch is somewhat con¬ 
flicting. The fluviatile and land-shells are all of existing 
species, but their geographical range has not always been 
the same as at present. Some, for example, which then lived 
in Britain are now only found in Norway and Finland, prob¬ 
ably implying that the Post-pliocene climate of Britain was 
colder, especially in the winter. So also the reindeer and 
the musk-ox [Ovibos ^noschatiis)^ now inhabitants of the 
Arctic regions, occur fossil in the valleys of the Thames and 
Avon, and also in France and Germany, accompanied in 
most places by the mammoth and the'woolly rhinoceros. 
At Grays in Essex, on the other hand, another species both 
of elephant and rhinoceros occurs, together with a hippopot¬ 
amus and the Cyrena flitminalis^ shell now extinct in Eu¬ 
rope but still an inhabitant of the Nile and some Asiatic 
rivers. With it occurs the JJnio littoralis^ now living in the 
Seine and Loire. In the valley of the Somme flint tools have 
been found associated with Hippopotamus major and Cyrena 
fluminalis in the lower-level Post-pliocene gravels; while in 
the higher-level (and more ancient) gravels similar tools are 
more abundant, and are associated witb the bones of the 
mammoth and other Post-pliocene quadrupeds indicative of 
a colder climate; 
It is possible that we may here have evidence of summer 
and winter migrations rather than of a general change of 
temperature. Instead of imagining that the hippopotamus 
lived all the year round with the- musk-ox and lemming, we 
'we may rather suppose that the apparently conflicting evi¬ 
dence may be due to the place of our observations being 
near the boundary line of a northern and southern fauna, 
either of which may have advanced or receded during com¬ 
paratively slight and temporary fluctuations of climate. 
There may then have been a continuous land communication 
between England and the North of Siberia, as well as in an op¬ 
posite direction with Africa, then united to Southern Europe. 
In drift at Fisherton, near Salisbury, thirty feet above the 
river Wiley, the Greenland lemming and a new species of 
the Arctic genus Spermophilus have been found, along with 
the mammoth, reindeer, cave-hyaena, and other mammalia 
suited to a cold climate. A flint implement was taken out 
from beneath the bones of the mammoth. In a higher and 
older deposit in the vicinity, flint tools like those of Amiens 
have been discovered. Nearly all the known Post-pliocene 
quadrupeds have now been found accompanying flint knives 
or hatchets in such a way as to imply their coexistence with 
