ft. 





'•:: 



% 

 % 





and 



lrin 



• 



9 



rical, 

 -live 



, 



.elta 



J 



is at 

 lr of 



eatl 

 the 



»r 



3 



ite 





the 



four 



v 





on 







*r of 







6,8 



auds 



^ the 



ionld 

 'feet 

 very 











Ch. xyiil] 



LAKE OF GENEVA. 



419 



number of years the Leman Lake will be converted into dry 



land. 



difficult to obtain the elements 



for such a calculation, so as to approximate at least to the 



quantity of time required for the 



plishment 



the 



l 



esult. 



The number of cubic feet of water annually dis- 

 charged by the river into the lake being estimated, experi- 

 ments might be made in the winter and summer months, to 

 determine the proportion of matter held in suspension or in 

 chemical solution by the Rhone. It would be also necessary 

 to allow for the heavier matter drifted along at the bottom, 

 which might be estimated on hydrostatic principles, when 

 the average size of the gravel and the volume and velocity of 

 the stream at different seasons were known. Supposing all 

 these observations to have been made, it would be more easy 

 to calculate the future than the former progress of the delta, 

 because it would be a laborious task to ascertain, with any 

 degree of precision, the original depth and extent of that 

 part of the lake which is already filled up. Even if this 

 information were actually obtained by borings, it would only 

 enable us to approximate within a certain number of centu- 



time when the Rhone beo*an to form 



delta ; but this would not give us the date of the origin of 



may 



have flowed into it for thousands of years, without importing 

 any sediment whatever. Such would have been the case, if 

 the waters had first passed through a chain of upper lakes ; 

 and that this was actually the fact, 



seems 



course of the Rhone between Martigny and the Lake of 

 Geneva, and, still more decidedly, by the channels of many 

 of its principal feeders. 



If we ascend, for example, the valley through which the 

 Dranse flows, we find that it consists of a succession of 

 basins, one above the other, in each of which there is a wide 

 expanse of flat alluvial lands, separated from the next basin 

 by a rocky gorge, once perhaps the barrier of a lake. The 



to have filled these lakes, one after the other, 



seems 



it 



some 



is still gradually eroding to a greater depth. Before, 

 therefore, we can pretend even to hazard a conjecture as to 



E E 2 



