190 Notice of Prof. Forbes 's Travels in the Alps. 



must not disturb a rocking stone, is pregnant with danger. All is on 

 the eve of motion. Let him sit awhile, as I did, on the moraine of Mi- 

 age, and watch the silent energy of the ice and sun. No animal ever 

 passes, but yet the silence of death is not there ; the ice is cracking 

 and straining onward — the gravel slides over the bed to which it was 

 frozen during the night, but now lubricated by the effect of the sun- 

 shine. The fine sand detached loosens the gravel which it supported — 

 the gravel the little fragments, and the little fragments the great ; till, 

 after some preliminary noises, the thunder of clashing rocks is heard, 

 which settle into the bottom of some crevasse, and all is again still. 1 ' 



Among the many dangers encountered in travelling through tfiese re- 

 gions, not the least arises from the fall of stones. " A stone, even if 

 seen beforehand, may fall in a direction from which the traveller, en- 

 gaged amidst the perils of crevasses, or on the precarious footing of a 

 narrow ledge of rock, cannot possibly withdraw in time to avoid it, and 

 seldom do they come alone. Like an avalanche, they gain others du- 

 ring their descent. Urged with the velocity acquired in half rolling, 

 half bounding down a precipitous slope of a thousand feet high, they 

 strike fire by collision with their neighbors — are split perhaps into a 

 thousand shivers, and detach by the blow a still greater mass ; which 

 once discharged, thunders with an explosive roar upon the glacier be- 

 neath, accompanied by clouds of dust or smoke produced in the col- 

 lision. I have sometimes been exposed to these dry avalanches ; they 

 are among the most terrible of the ammunition with which the genius 

 of these mountain solitudes repels the approach of curious man. Their 

 course is marked on the rocks, and they are most studiously avoided by 

 every prudent guide." 



The story of the debacle of the Val de Bagnes in 1818, is adverted 

 to, p. 262, and Prof. Forbes became acquainted with the very ingenious 

 engineer, M. Venetz, who so ably endeavored to arrest the catastro- 

 phe of Martigny. The event has been often adverted to in geological 

 travels. A mountain torrent formed by the snow floods, augmenting the 

 river Drause, which was dammed up by the ice, formed a lake one 

 mile and a half long, seven hundred feet wide and at one part two hun- 

 dred feet deep. This dam M. Venetz sluiced by a canal six hundred 

 feet long, with the labor of thirty four days, but the ice gave way and 

 " a deluge of five hundred millions of cubic feet of water was let loose, 

 in the space of half an hour, to sweep through a tortuous valley full of de- 

 defiles, literally with the besom of destruction. A flood five times greater 

 than that of the Rhine at Basle, filled the bed of a mountain torrent. In 

 the short space of its course from Getroz to Chable, the fall is 2,800 

 feet ; its acquired velocity was therefore enormous at the commence- 

 ment of its course, thirty three feet in a second, and therefore its power 



