FELIS SPELADA. 159 
its author discovered the skull of a Musk-sheep at Crayford, which of all the arctic mam- 
mals now alive rejoices the most in a severe climate. How the remains of the megarhine 
or southern species of Rhinoceros, could lie side by side with those of the most northern 
in habit of the herbivora, in the same river-bed, is a problem very hard to solve. Could 
the two animals have coexisted under the same climate in the same area? So far as we 
know of the former range of the one and of the habits of its living analogue,’ and of 
the habits of the other, it would have been impossible. There is, however, one view which 
has the merit of explaining this conflict of evidence, and which therefore is probably 
true. During the depression of North Germany and the greater portion of Britain, those 
portions of the Pliocene Continent now represented by France and the south of England 
were not submerged, for in that case they would present some traces of the deposit of the 
icebergs that were so numerous in the North Sea of the period; it is hardly within 
reason to suppose that all proof of submergence beneath the Glacial sea should have been 
removed by subaérial denudation from so large an area, while to the north of the Thames 
and in North Germany it is so abundant and so ample: it is, therefore, probable that 
the Thames Valley roughly marks the ancient coast-line of the Glacial sea in Britain, 
and that to the south the Pliocene land extended through France into Italy, while to the 
north the look-out was over a dreary expanse of sea, burdened with icebergs, like that off 
the coast of Newfoundland. ‘The temperate Pliocene climate must of course have been 
lowered by the presence of so much melting ice as is implied by the presence of the boulder- 
clay, and especially in the neighbourhood of its coast-line, independently of any great 
change flowing from some other unknown and cosmical cause. ‘This climatal change 
must have banished to a certain extent the Pliocene mammalia from the area over which 
it was felt; but, nevertheless, it is highly consistent with what we know of the migration 
of the herbivores to suppose that now and then some of the Pliocene mammals, such as 
Rh. megarhinus, may have ventured northwards as far as the shores of the great glacial 
sea. Again, M. Lartet® has proved that the Quaternary mammals invaded Europe 
from their ancient home in Siberia, where they dwelt during the Pliocene epoch, 
at the commencement of the European Quaternary period; the change in the 
Pliocene temperature coupled very possibly with the depression of land in North 
Siberia causing the animals inhabiting that area to advance westwards and to occupy 
the feeding grounds till then belonging to the Pliocene Fauna. This immigration very 
probably began at the time that North-Eastern Europe was being depressed beneath the 
waves during the Boulder-clay epoch. If this be admitted there is nothing improbable 
in the hypothesis that the arctic immigrants would gradually creep round the shores of the 
glacial sea, and here and there occupy in the winter the same pastures that afforded food 
to Pliocene mammals in the summer. ‘Thus, the remains of mammals indisputably 
Pliocene may have been commingled in the deposits of the same stream. In this way the 
1 See ‘Nat. Hist. Rev.,’ No. xix, p. 339, 1865. 
2 «Comptes Rendus,’ p. 409, et seq., 1898. 
