Alpine Valleys and Alpine Lakes. 93 



lake-basins by glaciers, and by them shot out as rubbish on the 

 margin of the plain, before the latest invasion of the sea, exactly 

 in the same manner as we know that the still existing moraines 

 were at a later period deposited. If the sea rose before the 

 glaciers retired to the upper valleys, ice-rafts of great dimensions 

 laden with moraine would have floated down the fiord-like inlets, 

 and would have rapidly melted on reaching the open sea. When- 

 ever this did not rise much above the present level of the lakes, 

 it is likely that the materials of the diluvium were accumulated 

 near the lower end of each lake by the stranding of the ice-rafts 

 on the shallow bar. It is even doubtful whether some supposed 

 moraines have not been formed in this manner. In either or 

 both of the two modes here indicated (by a solid causeway of 

 ice, or by floating ice-rafts) I believe that the diluvium, as well 

 as the more recent glacial deposits, have been borne from the 

 central regions of the Alps to the plains of northern Italy ; and 

 I am the more persuaded of this because I know of no other 

 means by which so vast a mass of solid materials could have 

 been carried so great a distance. The action of running water 

 has been perhaps underrated of late as a means of cutting a 

 passage through even hard rock; but it is difficult to think too 

 meanly of it as an agent for the transport, on a great scale, of 

 solid fragments over a wide space, such as intervenes between 

 the St. Gothard and the plain below Arona, or between the 

 Stelvio and Monza, the one distance approaching near to, the 

 other considerably exceeding, 100 miles. Fine sand and finer 

 mud are carried in vast quantities by existing currents ; but 

 even where these appear to bring down rolled specimens of the 

 rocks that surround their sources, it generally turns out that 

 such pebbles are picked out from some ancient ice-borne de- 

 posits lying near the banks or in the bed of the stream. The 

 effects even of such exceptional events as the well-known flood 

 in the valley of the Drause, the like of which recur at intervals 

 in every part of the Alps, are limited within very moderate 

 limits; and, though, the Lake of Geneva were filled up to facili- 

 tate the transport, I doubt whether a million of Drause-floods 

 would bear any appreciable amount of diluvium to the site of 

 the city of Geneva. 



If this were the proper occasion, there are many observations 

 in M. Mortillet's valuable papers that deserve further discus- 

 sion, and some of the details in his sketch of the ancient glaciers 

 of northern Italy, to which I should be inclined to except; but 

 I pass these over, and also forbear some remarks which I might 

 offer upon two interesting papers by M. E. Desor, wherein the 

 writer attempts a classification of alpine lakes, which, saving 

 some details, seems to me founded on just views. 



