388 CLIMATIC CONDITIONS OF THE GLACIAL EPOCH. 



regions, if po placed as to be out of the range of such winds, are only slightly 

 covered with snow and are not the home of extensive glaciers. 



We have learned that even in the high Polar latitudes, where the mean 

 temperature is very low, much the larger part of the surface is free, during 

 a considerable part of the year, from snow, and of course entirely destitute 

 of glaciers. This is by far the most important point which we have been 

 able to make in reference to the inquiry which forms the special subject of 

 the present volume. Since a vast area of land remains uncovered by ice in 

 spite of a low mean temperature, we are fully justified in asserting that a 

 still greater increase of cold would not cover those regions with ice, or bring 

 about the conditions of a Glacial epoch. On the contrary, it is evident that 

 the opposite result would take j^lace, or that those regions would become 

 still more free from snow and ice than they are at the present time. The 

 conditions of a Glacial epoch are not, therefore, to be sought for in a general 

 diminution of the temperature. It is true that the regions in which the gla- 

 ciers take their rise cannot be so warm that precipitation takes the form of 

 rain ; but the required low temperature must be confined to a limited area, 

 and be brought about by local causes, and not be something in which all 

 the other portions of the earth are sharers. There must be copious precipi- 

 tation, which, although locally in the form of snow, can in reality only be the 

 result of a high mean temperature in other regions. In short, warmth, as a 

 phenomenon of general occurrence, is more indispensably necessary than cold, 

 because the latter may always be produced, where locally wanted, by increase 

 of elevation or by the shifting of the ocean currents. 



The present writer is by no means the first to advocate the idea that a 

 higher mean temperature was compatible with a greater extension of the 

 glaciers. Already, as early as 1847, Lecoq took similar ground, defending 

 his views with great skill ; * although at the time his work was written the 

 lack of accurate observation over so large a portion of the earth's surface 

 placed him in a comparatively disadvantageous position, and he was hardly 

 able to find a single geologist to support him. The present writer holds 

 essentially the same views as those maintained by Lecoq, at least so far as 

 concerns the here all-important point of the existence of larger ice masses 

 being compatible with a higher mean temperature,! but has reached this 



* See Lecoq's work, entitled Les Glaciers et les Climats, on ties Causes Atmospheriques en Geologie, Paris et 

 Strasbourg, 1847. 



t A single quotation from Lecoq's work will be all for which room can be spared : "Thus the phenomenon 



