200 
ISLAND LIFE. 
[part I. 
glaciation might be produced, which would be specially intense 
during periods of high excentricity ; and it is to such causes we 
must impute the indications of ice-action in the vicinity of the 
Alps during the Tertiary period. The Permian glaciation appears 
to have been more extensive, and it is quite possible that at 
this remote epoch a sufficient mass of high land existed in 
our area and northwards towards the pole, to have brought on a 
true glacial period comparable with that which has so recently 
passed away. 
Estimate, of the comparative effects of Geographical and 
Astronomical Causes in producing Changes of Climate. — -It 
appears then, that while geographical and physical causes alone, 
by their influence on ocean currents, have been the main agents 
in producing the mild climates which for such long periods 
prevailed in the Arctic regions, the concurrence of astronomical 
causes — high excentricity with winter in aphelion — was neces- 
sary to the production of the great glacial epoch. If we reject 
this latter agency, we shall be obliged to imagine a concurrence 
of geographical changes at a very recent period of which we 
have no evidence. We must suppose, for example, that a large 
part of the British Isles — Scotland, Ireland, and Wales at all 
events — were simultaneously elevated so as to bring extensive 
areas above the line of perpetual snow ; that about the same 
time Scandinavia, the Alps, and the Pyrenees received a similar 
increase of altitude ; and that, almost simultaneously, Eastern 
North America, the Sierra Nevada of California, the Caucasus, 
Lebanon, the southern mountains of Spain, the Atlas range, and 
the Himalayas, were each some thousands of feet higher than 
they are now ; for all these mountains present us with indica- 
tions of a recent extension of their glaciers, in superficial phe- 
nomena so similar to those which occur in our own country 
and in Western Europe, that we cannot suppose them to belong 
to a different epoch. Such a supposition is rendered more diffi- 
cult by the general concurrence of scientific testimony to a partial 
submergence during the glacial epoch, not only in all parts of 
Britain, but in North Amerioa, Scandinavia, and, as shown by 
the wide extension of the drift, in Northern Europe ; and when 
to this we add the difficulty of understanding how any probable 
