ORIGIN OP VALLEY-LAKES. 73 



7. On the Origin of Valley-lakes, with especial reference to the 

 Lakes of the Northern Alps. By the Kev. A. Irving, B.A., 

 B.Sc, F.G.S. (Read, December 20, 1882.) 



This paper is intended as nothing more than a supplement to a 

 paper by the author on the Mechanics of Glaciers. The main 

 strength of the position taken ' up by the advocates of the glacier- 

 excavation theory is derived from arguments which labour to show 

 that it is the only feasible hypothesis *. I have endeavoured to 

 show in my previous paper that this hypothesis is inadmissible on 

 mechanical and physical grounds ; all I attempt to do here is to 

 show that we are not shut up to the hypothesis ; for many agencies 

 can be pointed to which may have cooperated to form lake-basins, 

 some of which have hardly been considered with sufficient care, 

 while others would appear to have been ignored. In dealing more 

 especially with the lakes of the Northern Alps, I have simply 

 selected a region which abounds in lakes occupying expansions of 

 river-valleys which I know pretty intimately from direct obser- 

 vation, including a district already treated more in detail by Prof. 

 Bonney t. jSTor do I pretend either that all which is here advanced 

 is new to geology, or that I am able to give an exhaustive account 

 of all the agencies which have helped to form lake-basins past and 

 present. Many lakes also, for example such as those which occupy 

 the craters of extinct volcanoes in the Eifel and elsewhere, are 

 excluded from consideration here by the title of the paper. 



I shall first draw attention to what appear to me defects in the 

 arguments of the excavationists, as propounded by Sir A. Ramsay 

 himself, by which they would shut us up to the " excavation 

 hypothesis." 



1. With reference to these Alpine lakes, the position of some of 

 them is very difficult to. account for if they were excavated by the 

 great glaciers which, during the Glacial Epoch, moved mainly from 

 the central chain of the Alps towards the low-lying country. 



The position, f or example, of such lakes as Neuchatel, the Bodensee, 

 the Wallensee, the main portion of the Vierwaldstattersee, and the 

 lakes lying in the Traun valley above Aussee would be very difficult to 

 explain in this way, especially if we take into account also the con- 

 tours of their basins. Seeing the thing in three dimensions, as in 

 nature, gives a truer idea than the representation of it in two dimen- 

 sions only, as on a map. 



2. The argument against lakes lying in valleys formed by 

 synclinal folds of the strata, so far as it goes, seems to overlook 

 altogether the frequent occurrence of valleys lying along the axes of 



* Vide Prof. Ramsay's paper, Quart. Journ. Geol. Soc. 1862. The arguments 

 put forward in this paper have been recently summarized by Sir A. Ramsay in 

 his 'Physical Geology and Geography of Great Britain,' 1878. 



t Quart. Journ. Geol. Soc. vol. xxix. p. 382. 



