190 



the edge of the lake, and passing on in the same direction, below the 

 lake, till, owing to the check of the water, it comes to an abrupt ter- 

 mination, and stoops suddenly down. In the case of the Lake of 

 Lungern, on the water being withdrawn, the stream, no longer re- 

 ceived into a body of still water, has begun to cut down its delta, as 

 the Niagai'a River cuts through the sti-ata on which it runs, until a 

 deep channel is formed all the way back to the mountains, the re- 

 moved matter being, of course, carried forward into the receded wa- 

 ters of the lake. This the author of the paper regarded as an ex- 

 planation of the formation of alluvia in valleys, and their subsequent 

 intersection. The detritus was received into a body of water occu- 

 pying the valley ; on that being withdrawn, the river was allowed to 

 cut down and form a channel for itself in the alluvial sheet. A num- 

 ber of reasons were adduced for believing that, in general cases, this 

 recipient body of water was the sea. 



A description was given of an ancient lake-bed in the vale of 

 Chamouni, the barrier of which was the right side moraine of the 

 anciently more extended Glacier des Bois or Mer de Glace. Some 

 notices were appended regarding smoothings of fixed surfaces and 

 zones of erratic blocks in Switzerland, and an endeavour was made 

 to establish the probability of icebergs borne on the sea having been 

 concerned in producing some of those phenomena. It was particu- 

 larly remarked that the zone of blocks at Monthey was just about the 

 same height above the present level of the sea (1670 feet) as the 

 uppermost of the terraces at Vevay ; while M. Saussure had found 

 traces of running water on Mont Saleve, at the height of the cele- 

 brated eri'atics above Neufchatel. 



These facts were not presented in opposition to the doctrine of a 

 former greater extent for the glaciers, which was, on the contrary, 

 admitted, though not to the extent demanded by some previous ob- 

 servers. Different agencies, or the same agencies differently applied, 

 might, the author thought, often lead to nearly similar effects. 



2. On the Classification of Colours. By Professor J. D. 

 Forbes. 



As the reading of this paper was only commenced at this 

 meeting, the abstract is deferred until the conclusion. 



