286 CLIMATIC CONDITIONS OF THE GLACIAL EPOCH. 



It is not until we reach the Caucasus, in travelling east, that we come again 

 upon perpetual snow. 



The most important of the glacier s^ystems of the Alps are those grouped 

 around Mont Blanc, Monte Rosa, and the so-called Bernese Oberland. The 

 culminating points of these are Mont Blanc, 15,784 feet; Monte Rosa, 15,217, 

 and the Finsteraar Horn, 14,026. The area covered by snow and ice in the 

 Bernese Oberland is somewhat more than a hundred square miles in extent. 

 Here is the largest glacier of the Alps, that called the Aletsch, which has 

 a length of nearh' fifteen miles with an average breadth of fully one mile. 

 The Mer de Glace of the Mont Blanc system is about eight miles in length, 

 reckoning from its termination below to the crest of the range at the head 

 of the Glacier du Geant. 



The height of the snow line on the Alps is given by H. von Schlagintweit 

 at 9,200 feet for the southern side, and 8,900 for the northern. The mean 

 temperature at that line is stated, on the same authority, to be — 4° (C). 

 Where the topographical conditions are favorable — that is, where there is 

 a large gathering ground, the precipitation of which must all be conveyed 

 away in one channel — there the glaciers are longest and reach nearest 

 to the sea-level, as a glance at the various detailed maps of the Alpine 

 gliicier regions will instantly show.* Thus the termination of the Mer de 

 Glace is given on Forbes's map, published in 1843, at 3,667 feet above the 

 sea-level. Several of the Alpine glaciers come down to about 4,000 feet, 

 while, as already mentioned, those of tlie Caucasiis do not usually descend 

 much below 8,000 feet, for reasons which have been already explained. 



The glacial system of the Pyrenees is very much less important than that 

 of the Alps. There are several reasons for this. One important one is, that 

 the absolute elevation of the range is lower, its culminating point, Nethou, 

 reaching only 11,167 feet. Besides this, the Pyrenees form a chain of great 

 simplicity of orographic structure, so that its breadth is very small compared 

 with its length. Hence there are no such great gathering grounds for the 

 glaciers as there are in the Alpine range. Again, the precipitation is less, 

 and especially on the south side of the chain. In consequence of these com- 

 bined conditions the ice fields rarelv have the lono-itudinal extent of even 

 the smaller Alpine glaciers. To use the words of a careful explorer of the 

 range. " they are, rather, great irregular and undulating surfaces coveiing 

 the slopes or the summits, but wiihout descending and winding through the 



* See for the Mont Blanc district the beautiful m:ip of VioUet-le-Duc (Paris, 1S76). 



