13 
YORKSHIRE naturalists' UNION. 
especially from a warm to a cold climate, would })robably prove fatal 
in a majority of cases with most organisms, yet the gradual changes 
encountered during natural migration are far from insuperable; 
indeed, according to Darwin, acclimatization is readily effected during 
a longcoui se of gradual migration, species being probably limited in 
range more by competition than by climate. 
Dr. Scharff accepts the reality and seriousness of this life struggle 
and recognizes the forcible restriction and retreat of the earlier 
evolved and more primitive forms to Arctic and other weaker regions 
and instances the Arctic and Alpine Hare (Lcpus variahiUs) which, 
though formei ly overspreading great parts of the northern hemisphere, 
has now in European regions owing to the competition of the later 
evolved and more dominant European Hare {Lppuf^ europceas) now 
been driven from its former haunts in the plains into Alpine and 
Arctic lands, except in lieland, where it still occupies the plains 
because the European Hare has not yet penetrated there, and he 
remarks that "it is not tlie cold that has driven the Alpine Hare to 
the Alps, and its presence there is nut, as is often supposed, a 
standing testimony of a former Arctic climate in Europe, but merely 
the necessaiy consequence of the weaker species being thrust into 
less accessible regions by a stronger rival." 
That the alternate warm and cold periods which characterized the 
Miocene and (ilacial epochs, whether these have resulted from the 
excentricity of the earth's orbit, the pendulation of the earth's rotatory 
axis, or from other causes, must be conceded to have had considerable 
influence on the dispersal of life, though none on the laws governing- 
it ; yet the rigours and effects of the glacial age have probably been 
overestimated, for in North Siberia, the very coldest region of the 
world, with an intensity of frost far beyond what is claimed to have 
existed in these islands during that period, and showing a mean 
annual temperature of more than 27° of frost, descending in winter 
to 80° below the freezing point, yet great forests exist and the very 
finest furs are obtained therefrom, while in Alaska forests are known 
to flourish even upon the actual surface of the glaciers themselves, 
and we cannot but legard the extreme views of some geologists on this 
subject as untenable, as it would seem reasonably certain that the 
native fauna and Hoia of" these islands were not exterminated, but 
in great part persisted through the glacial age. 
Mr. Clement Reid, the well-known glacialist, has declared that in the 
district wheie London now stands, the mean annual isotherm during 
the greatest severity of the Ice age was 8u" Fahr., a temperature 
C()mi)arable with that of \orth Norway, Manchuria, British Columbia, 
etc., at the present day, and these are all countries which possess a 
comparatively rich and varied fauna and flora ; while according to 
the studies of Prof. Neumayr and others to determine the temperature 
of Europe during the Ice age, based upon the present and former 
positions of the snow-line, it has been shown that the climate of 
Central Europe was probably not more than about 6° Cent, colder 
