Valleys of the Bhine and Bhone. 157 



it. This indicates a former level of the sea at least 2000 feet 

 above the present. In the connected valley called the Sim- 

 menthal, there are such ancient alluvial formations ascending 

 to even a greater height, their range being between 2200 and 

 3000 feet above the present level of the sea. I fortunately 

 have not to stand unsupported in these particulars ; for, ac- 

 cording to Mr Playfair, Saussure '* found proofs of the running 

 of water on the side of Mont Saleve, at least 200 toises above 

 the present supei'ficies of the lake (of Geneva) ;" that is, at a 

 total elevation above the sea of at least 2507 feet. 



Before parting with this subject, we must revert for a 

 moment to the alluvial sheet at the junction of the Arve and 

 Rhone. Under the light which we now have regarding the 

 circumstances necessarily attending such formations, we 

 might safely affiliate the whole of that sheet to the Arve, 

 even if the rocks of which it is composed did not tell the 

 same tale. Undoubtedly, the Arve has discharged the whole 

 of this matter into the valley of the Rhone, while there was 

 a body of still water at a sufficient height to receive and 

 spread it out. It was, in fact, a subaqueous deposit thrown 

 across the valley as a sort of barrier at this place, and such 

 must have been its character, when first the withdrawal of 

 the recipient body of water left it fully exposed. As a bar- 

 rier, its function was to confine the waters of Lake Leman, 

 which originally would stand at least a hundred feet above 

 their present level, and so would continue to do till the 

 Rhone had worn out the trough or valley in which the city 

 of Geneva now stands. The wearing of this trough, it may 

 be remarked, has only produced a partial reduction of the 

 blockage, so that it may still be said, that this detrital dis- 

 charge of the Arve in an early age, is the immediate cause 

 of Lake Leman, at least of there being a lake at this place of 

 precisely such a level. For many of the lakes of our own 

 country, I believe that an origin could be traced in exactly 

 such a course of events in the alluvial period. 



Ancient Lake-Beds, 

 Two unequivocal instances of ancient lake-beds occur in 



