the climatic aspects from a physical, zoological, and
botanical point of view.

According to Professor Penck (_a_, p. 12), the nature of the glacial
climate can be determined by comparing the snow-line of the Glacial
period with that of the present day. The position of the snow-line is
dependent on two climatic factors--viz., precipitation and temperature.
We know the height at which snow must have lain permanently during the
Glacial period, or during the maximum phase of glaciation. If the Ice
Age had been produced solely by an increase of snowfall, as has been
suggested, Professor Penck tells us that then it must have snowed three
or four times as much as it does now. But he does not adopt the view
that the Ice Age is due to an increase of snowfall alone. His
calculations, based upon the height of the snow-line, tend to show that
a general decrease of temperature to the extent of from 4-5 degrees
Centigrade (all other atmospheric conditions remaining the same as now)
would be sufficient to give us back the Glacial period.

Professor Neumayr (p. 619) adopted a similar principle in determining
the temperature which prevailed in Europe during the Glacial period.
Snow now lies in the Pyrenees 1000 metres higher than it did then, 1,200
metres higher in the Alps, and 800 metres higher in the Tatra mountains.
Since the temperature in Central Europe decreases by half a degree
Centigrade for every 100 metres of elevation, it follows that if the
glacial phenomena had only been brought about by a decrease of
temperature without an increase of moisture, we should have had a
reduction of temperature during the Glacial period of six degrees
Centigrade in the Pyrenees, of seven degrees in the Alps, and of four in
the Tatra mountains. The general lowering of the temperature of Europe,
says Professor Neumayr, could not have amounted to more than six degrees
Centigrade. Moreover, he is of opinion that the very low snow-line in
the British Islands proves that even during the Ice Age a comparatively
mild climate prevailed there, and that the climatic conditions
generally, in the different parts of Europe, were relatively about the
same as they are now.

Professor J. Geikie does not give us his views as to the temperature of
the Glacial period, but he maintains that a lowering of the temperature
is evinced not only by the widespread phenomena of glaciation, but by
the former presence in our temperate latitudes of a northern fauna and
f