NOTES ON THE THICKXKSS OF THE LUCKRNE GLACIER, ETC. 287 



to the lieiglit at which we stand, and that all the lofty heights 

 and terraces above and around were enveloped in a perennial 

 mantle of snow. In a word, to reproduce to the mind the 

 present scene as it was during the Glacial epoch, we must 

 ascend the higher valleys of the Bernese Oberland seen in the 

 distance, and stand on the clififs overlooking the Mer de Glace 

 under the slopes of Mount Blanc, at a height of 10,000 feet 

 above the level of tlie sea. Such is the transformation scene 

 indicated by the phenomena visible at intervals as we wander 

 along the dense forests or open glades around, at a level of only 

 about 2,780 to 2,800 feet above "the sea. 



There is, of course, nothing new in what has been stated 

 above. The late Sir Andrew Ramsay in his memorable essay 

 entitled " The Glacial Origin of Lakes," recognised that the 

 valley of the Lake of Lucerne was once the channel of a 

 " great jrlacier," and shows that the lake itself lies in a " rock 

 basin," being deeper in the central part than at the outlet ; 

 and he overthrows the view — at that time held by some Swiss 

 geologists — but, I presume, now generally discarded, that the 

 lake occupies the space left by " a gaping fissure."* The fact 

 that the present glaciers of the Alps once descended so low 

 as to till the valleys of the great lakes, rising high on their 

 banks, has been recognised since the days of De Saussure, 

 Charpentier,t and others. Their former extension is testified to 

 by the occurrence of boulders of gneiss, granite and protogene 

 derived from the central core of the Alps, lying scattered over 

 the sides of the valleys formed of the more recent formations 

 of Cretaceous and Tertiary strata, for the most part composed 

 of fossiliferous limestone and shale ; while the surfaces of the 

 rocks themselves are often polished and worn by glacial 

 grooves and striations at long distances from the nearest 

 limits of the existing glaciers. This being so, it occurred to 

 me, while endeavouring to realise on the spot, during the late 

 summer, the physical change that has taken place, to endeavour 

 to measure with some approacli to accuracy the actual depth to 

 which the glacier of the Lucerne valley attained during its 

 period of maximum evolution. 



Tortunately the data for the solution of this problem are not 

 wanting, and I hope to make it clear how they are to be 

 applied. 



C^jyer limit of Glacier action how def'^rmined.— The height 



* Quart. Jouni. Geol. Soc, vol. xviii, p. 196. Eamsay makes the depth 

 of the lake 853 feet, which would be probably ne.u- tiie centre opposite 

 Vitznaii. f Essai syr les Glaciers. 



