of the Glacial Epoch. 325 



have imagined that the heat emitted by the sun is subject to 

 variation, and that this epoch was the result of what may be 

 termed a cold solar period. Mr. W. Hopkins believes that a 

 different distribution of land and water, and especially a different 

 direction of the currents of warm water which set from the tro- 

 pical towards the polar oceans, would render the climate of cer- 

 tain localities colder than it is at present, and would thus suffi- 

 ciently account for the phenomena of the glacial epoch. Finally, 

 Professor Kamtz* considers that at the time of the glacial period 

 the mountains were much higher than at present, Mont Blanc 

 reaching an altitude of 20,000 feet for instance, the secondary 

 and tertiary formations having been removed from their summits 

 during the glacial epoch. 



The two last assumptions are attended with formidable geolo- 

 gical difficulties, especially when it is considered that the phe- 

 nomena of the epoch in question extended over the entire surface 

 of the globe ; they have therefore never acquired more than a 

 very partial acceptancef. The first two hypotheses, again, have 

 been recently shown by Tyndall to be founded upon an entirely 

 erroneous conception of the conditions necessary to the pheno- 

 mena sought to be explained. The formation of glaciers is a 

 true process of distillation, requiring heat as well as cold for its 

 due performance. The produce of a still would be diminished, 

 not increased, by an absolute reduction of temperature. A greater 

 differentiation of temperature is required to stimulate the ope- 

 ration into greater activity. Professor Tyndall does not sug- 

 gest any cause for such exalted differentiation during the glacial 

 epoch ; but he proves conclusively that both hypotheses, besides 

 being totally unsupported by cosmical facts, are not only incom- 

 petent to constitute such a cause, but also assume a condition of 

 things which would cut off the glaciers at their source, by dimi- 

 nishing the evaporation upon which their existence essentially 

 depends. Only by a greater difference of temperature between 

 land and ocean is an increase of glacial action possible; and 

 these hypotheses fail, inasmuch as they ignore altogether the 

 necessity for such an augmentation of thermal difference. 



* Miltheilungen der Ic.-Tc. geographischen Gesellschaft zu Dorpat, vol. ii. 



t Speaking of the glacial epoch, Ramsay says (Quart. Journ. Geol. Soc. 

 for 1862, p. 204), " I find it difficult to believe that the change of climate 

 that put an end to this could be brought about by mere changes of physical 

 geography. The change is too large and too universal, having extended 

 alike over the lowlands of the northern and the southern hemispheres. The 

 shrunken or vanished ice of mountain-ranges is indeed equally character- 

 istic of the Himalaya, the Lebanon, the Alps, the Scandinavian chain, the 

 great chains of North and South America, and of other minor ranges and 

 clusters of mountains like those of Britain and Ireland, the Black Forest, 

 and the Vosges." 



