the Alpine Lakes and Valleys. 209 



tains its maximum depth (265 metres near Meillerie, and 300 

 metres a little further west *) . 



Nevertheless it is probable that in this locality the bed of 

 the lake is of the same nature as its banks, that is to say, lime- 

 stone, and that the ridges there consist of very hard lime- 

 stone. Further westward, where the lake is situated in Tertiary 

 Mollasse much softer than the limestone, it only attains a depth 

 of from 30 to 40 metres. 



This fact is of considerable importance. It seems to me 

 inexplicable, on the supposition that the glacier hollowed out 

 the basin of the lake ; on the other hand, it is easy of explanation 

 in connecting the depression of the lake with the inclination of 

 the strata. Near Meillerie the beds of hard limestone are vertical 

 and highly contorted, and there the lake is deep ; nearer Geneva 

 the softer beds of Mollasse descend from the two sides of the lake 

 beneath its waters with a gentle inclination, and there the lake 

 is shallower. This proves the relation between the depth of the 

 lake and the flattening of the beds, as has been already stated 

 by M. Studer; and I will show further on, that it is connected 

 with the reversal of the same beds. 



Let us now turn to another point. 



I consider that the observations made in the neighbourhood 

 of Geneva have contributed to the origin of that theory of the 

 erosion of the lakes, which I oppose. These observations may 

 be summed up as follows. 



Below the Lake of Geneva there are found considerable accu- 

 mulations formed in their upper part of glacial deposits (clay 

 with scratched pebbles and transported boulders), and in their 

 lower part of the older drift of Necker. This latter deposit 

 is different from the old drift of the greater number of the 

 savants who have written upon the geology of France. We have 

 also in our country this old drift, which is that which I have 

 distinguished in the explanation of my geological map of Savoy 

 by the name of terrace-gravel [alluvion des terraces). It contains 

 Elephas primigenius. Overlying the glacial drift, this last 

 is higher than the older drift of Necker, upon which I am 

 desirous of making a few remarks. This last is composed of 

 rolled pebbles and sand, often bound together by a calcareous 

 cement. No striated pebbles are seen amongst them. The 

 principal characters of this accumulation in our district consist 

 in its being of older date than the glacial deposit, in being 

 placed below the Lake of Geneva, and in enclosing pebbles (such 

 as those of euphotide) which could not have been derived from 

 the Valais, whence the Rhone glacier proceeded. 



* Chart of the principal soundings of Lake Leman, by H. T. De la 

 Beche, 1827. 



