PKOCEEDINGS OF GEOLOGICAL SOCIETIES. 



Ill 



not upon mean temperature, is evident from a comparison of its height on 

 the coast and in the interior of the Scandinavian peninsula, as given by 

 Forbes in the accompanying table, compiled partly from his own observa- 

 tions, and partly from those of Yon Buch, Naumann, and others. 



Thus the difference between the height of the snow-line near the coast, 

 where, owing to the impact of the gulf-stream, the winter is mild but the 

 atmospheric precipitation great, and in the interior, where the climate is 

 severe but the air comparatively dry, amounts in some cases to as much as 

 1050 feet, or nearly one-fourth of the total height. Such is the depress- 

 ing effect of greater precipitation as regards the limit of perpetual snow ; 

 nor must it be forgotten that copious precipitation is altogether incompa- 

 tible with great summer-heat. The incessantly clouded sky cuts off the 

 solar rays, and moderates the summer temperature. It is a trite observa- 

 tion, that a wet summer is always a cold one. The mean temperature of 

 the land in contiguity with such extensive surfaces of snow could also not 

 fail to be considerably reduced ; for although the actual amount of heat in 

 activity at the surface of the earth was greater during the glacial period 

 than subsequently, yet the cold of winter became stored up in masses of 

 falling snow, which in melting absorbed the heat of the succeeding summer, 

 and thus reduced both the mean and summer temperature of the land, es- 

 pecially of such portions of it as were not situated greatly below the snow- 

 line. The common notion, therefore, that the glacial epoch was a cold 

 one, is correct, although heat, not cold, was the cause of that epoch. This 

 apparent paradox, that heat should be the cause of cold, finds its parallel 

 in the ice-making machines which were in operation at the last Great Ex- 

 hibition. In those machines which produced from 2 to 12 tons of ice per 

 ton of coal, the glacial produce was directly proportional to the amount of 

 heat developed by the combustion of coal. 



But it is evident that this lowering of the snow-line by increased oceanic 

 temperature could only occur within certain limits ; for, although the 

 mean temperature of the snow-line might rise from 21°, its present posi- 

 tion in Norway, to 35°, its height under the equator, and perhaps even 

 still higher, without any elevation of the snow-line itself, yet a further 

 rise of mean temperature, which would result from a continued augmen- 

 tation of oceanic heat, could not fail to elevate the snow-line itself, and 

 eventually to chase the last portions of snow even from the loftiest moun- 

 tain peaks. A process the inverse of this has gone on in nature, leading 

 gradually to the glacial epoch, and eventually to the present meteorolo- 

 gical condition of our globe. Whilst the ocean maintained a high tem- 

 perature, the snow-line floated above the summits, possibly even of the 

 most lofty mountains ; but with the reduction of oceanic temperature it 

 gradually descended, enveloping peak after peak in a perennial mantle, 

 until during the glacial epoch it attained its lowest depression, whence it 

 again rose, owing to diminished evaporation, to its present position. 



The speaker considered that, inasmuch as recent researches had ren- 

 dered all previous hypotheses regarding the glacial epoch absolutely un- 

 tenable, the one for which he now contended could not be said to come 

 into antagonism with any other views. It also further commended itself 

 by requiring the assumption of no natural convulsion or catastrophe, no 

 vast or sudden upheavals or depressions, and no change in the thermal re- 

 lations of our earth to the sun or to space. On the contrary, it insisted 

 that the glacial epoch was normally and gradually evolved from a thermal 

 condition of the interior of our globe, which could scarcely be said to be 

 any longer the subject of controversy. 



In conclusion, this hypothesis suggests the probability that the other 



