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 awaj^ 



Estimate of the comparative effects of Geograpliical 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 w^e 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 America, 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 



