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climate, consists of species that have very different powers of 
resisting cold and heat. Thus the musk sheep is found now 
only under the lowest temperatures in the vast treeless, 
barren grounds of North America, while the reindeer lives 
also in the forests, along with the elk of the Europaeo- 
Asiatic and North American continents. The red deer and 
the bison range up to the edge of the province inhabited by 
the other animals. The lemmings live under a very severe 
climate, while the marmots are found in the higher and 
colder districts in Southern Europe and Central Asia. Each 
of these Northern species is dependent upon the oscillation 
of the climate for its particular habitat in a given year, 
retreating northward or southward according to the tem- 
perature that regulates the supply of food necessary for its 
existence. By some such oscillation of temperature the 
remains of the animals of two contiguous zoological pro- 
vinces may be found together in one spot, as in the case 
of the northward retreat of the musk sheep, from the neigh- 
bourhood of Fort Churchill, where it once lived, and which 
is now occupied by the elk and waipiti. In this manner the 
admixture of the remains of animals living at the present 
day, respectively in a severe and in a temperate continental 
climate, may be accounted for in the Pleistocene caverns and 
brickearths. 
The hypothesis of a series of conditions obtaining in 
Pleistocene Western Europe, similar to those now found in 
some portions of Northern Asia, is necessary to complete the 
evidence afforded by the fauna, and the deposits in which 
they are found. Now, the contortion of the gravels, and the 
angular state of the pebbles of which they are often composed, 
are, as Mr. Prestwich infers, explicable only on the theory 
of ice having been found in our rivers in far larger 
quantities than at the present day — the one being the result 
of the grounding of miniature bergs, the other of the melting 
away and depositing their burden of pebbles. The large 
