354 



FLOOD AT TIVOLI. 



[Ch. XV. 



plain of Martigny, it entered the Rhone, and did no farther 

 damage ; but some bodies of men, who had been drowned 

 above Martigny, were afterwards found, at the distance of 

 abont thirty miles, floating on the farther side of the Lake 

 of Geneva, near Vevay. 



The waters, on escaping from the temporary lake, intermixed 

 with nrad and rock, swept along, for the first four miles, at 

 the rate of above twenty miles an hour ; and M. Escher, the 

 engineer, calculated that the flood furnished 300,000 cubic 

 feet of water every second — an efflux which is five times 

 greater than that of the Rhine below Basle. Now, if part of the 

 lake had not been gradually drained off, the flood would have 

 been nearly double, approaching in volume to some of the 

 largest rivers in Europe. It is evident, therefore, that, when 

 we are speculating on the excavating force which a river may 

 have exerted in any particular valley, the most important ques- 

 tion is, not the volume of the existing stream, nor the present 

 levels of its channel, nor even the nature of the rocks, but the 

 probability of a succession of floods at some period since the 

 time when the valley may have been first elevated above the sea. 



Eor several months after the debacle of 1818, the Dranse, 

 having no settled channel, shifted its position continually 

 from one side to the other of the valley, carrying away newly- 

 erected bridges, undermining houses, and continuing to be 

 charged with as large a quantity of earthy matter as the fluid 

 could hold in suspension. I visited this valley four months 

 after the flood, and was witness to the sweeping away of a 

 bridge, and the undermining of part of a house. The greater 

 part of the ice-barrier was then standing, presenting vertical 

 cliffs 150 feet high, like ravines in the lava-currents of Etna 

 or Auvergne, where they are intersected by rivers. 



Inundations, precisely similar, are recorded to have occurred 

 at former periods in this district, and from the same cause. In 

 1595, for example, a lake burst and the waters, descending 

 with irresistible fury, destroyed the town of Martigny, where 

 from sixty to eighty persons perished. In a similar flood, fifty 

 years before, 140 persons were drowned. 



Flood at Tivoli, 1826. — I shall conclude with one more 

 example derived from a land of classic recollections, the 





