INTRODUCTION, XX XV 
of a former rich series of British Mammalia to its present 
scanty proportion, has been caused by human agency; and 
we may reasonably conjecture that the rest of the great 
change has been the consequence of a series of gradual 
and consecutive dyings-out of species; since certain con- 
ditions of the pliocene and post-pliocene Mammalia are 
irreconcilable with the hypothesis that they all simulta- 
neously perished by a sudden and violent catastrophe, like 
that which Cuvier deduced from the phenomenon of the 
Sh 
" 
frozen Mammoth.” Evidence will be given in the present 
work in proof, that the Elephants and Rhinoceroses of 
pliocene Britain, were adapted to live in a northern or 
temperate climate ; and since the Hippopotamus, their cou- 
temporary and associate, was a different species from the 
present African one, it might also have been able to exist 
beneath a less sultry sky than that of Africa. 
Thus, in the endeavour to trace the origin of our ex- 
isting Mammalia, I have been led by the researches de- 
tailed in the present work, to view them as descendants 
of a fraction of a peculiar and extensive Mammalian Fauna 
which overspread Europe and Asia at a period geolo- 
gically recent, yet incalculably remote and long anterior 
to any evidence or record of the human race. It would 
appear, indeed, from the comparisons which the present 
state of Paleontology permits to be instituted between the 
recent and extinct Mammalian Faune of other great natu- 
ral divisions of the dry land, that these divisions also seve- 
rally possessed a series of Mammalia, as distinct and peculiar 
in each, during the pliocene period, as at the present day.+ 
When such a comparison is restricted to the Fauna of 
a limited locality, especially an insular one like Great 
* See the interpretation of that striking fact in pp. 261, 270. 
+ See ‘ Report of the British Association,’ vo. 1844, p. 237. 
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