IxXXViii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Lake of !N'eucliatel flanks the soutliern slope of tlie Jura. "We may 

 at once admit that this region was formerly covered by a mighty 

 glacier, extending from Villeneuve at the mouth of the valley of 

 the Ehone to Greneva, Neuchatel, Bern, and Solothurn. Descend- 

 ing principally from the valley of the E,hone, this glacier is 

 assumed to have been 2780 feet thick at this spot, and 2200 feet 

 thick where it abutted against the flanks of the Jura near Neu- 

 chatel. But if we add to this the depth of a portion of the Lake 

 of Greneva, the total thickness of the ice was in some places 

 3764 feet. If, again, we look at the tract of country over which 

 this icy mantle was spread, we find it extending about 100 miles in 

 length, from Greneva to Solothurn, from S.W. to N.E., and upwards 

 of thirty miles in width between the Alps and the Jura. Now 

 the greater portion of this glacier must have come down the val- 

 ley of the Ehone by Sion, Martigny, and Bex, and this valley, par- 

 ticularly near its termination, cannot be more than two or three 

 miles in width, in many places not so mu.ch. The inclination 

 from Sion to Villeneuve is very slight ; and although it is probable 

 that the Alpine chain may have had a greater altitude during the 

 glacial period than at present, there is no reason for supposing 

 that the angle of inclination of the main valley down which the 

 great glacier advanced was greater than it is now, although that 

 of the smaller valleys, which also contributed their quota to swell 

 the moving mass, may have had a somewhat steeper inclination. 



Admitting then all this, and remembering the thickness of the 

 icy covering in the plain, I am at a loss to understand where we 

 are to look for that powerful agency, that vis a tergo, by which this 

 comparatively small mass could push forward at the very lowest 

 imaginable rate, the vast field of ice covering BOOO square miles of 

 the great plain of Switzerland, and yet with such irresistible 

 energy, and in a direction at right angles to its principal line of 

 movement, as to cause it to scoop otxt the rocky basin in which 

 the Lake of Greneva now lies. In his address to the Eoyal Geo- 

 graphical Society last year. Sir Eoderick Murchison has already 

 pointed out this difiiculty, and Prof. Eamsay has endeavoured to 

 meet it by showing (Phil. Mag. p. 300) that this great mass of ice 

 from the Ehone valley was " jDrodigiously swelled by the great 

 tributary glacier of Chamouni, which, descending from Mont 

 Blanc, filled a valley some fifty miles in length, and joined the 

 Ehone glacier near the lower end of the Lake of Geneva;" and 

 moreover, he adds, that " during the cold of the glacial epoch all 

 the higher region south of the lake must have maintained its 

 glaciers and filled the valleys that run north." 



Now, with all due submission to Prof. Eamsay's greater expe- 

 rience, I cannot avoid entertaining the opinion that the immediate 

 efl'ect of this Chamouni glacier, although adding to the accumulation 

 of ice in the great valley of Switzerland, must have had the eflect 

 of checking the momentum and progress of the Ehone glacier, if it 

 had any, towards the south-west, and of driving the two together 

 in a line of mean result against the flanks of the Jura. But leav- 



