Rev. A. Irving on the Origin of Valley -Lakes. 65 



December 20, 1882.— J. W. Hulke, Esq., F.R.S., 

 President, in the Chair. 



The following communications were read : — 



1. " On Generic Characters in the Order Sauropterygia." By- 

 Prof. Owen, C.B., F.R.S., F.G.S., &c. 



2. " On the Origin of Valley-Lakes, mainly with reference to the 

 Lakes of the Northern Alps." By the Rev. A. Irving, B.A., B.Sc, 

 F.G.S. 



The author, having given reasons for considering this question still 

 an open one, proceeded to criticise Prof. Ramsay's theory as it was 

 expounded by him in 1862. The defects in Prof. Ramsay's argu- 

 ment are, he considers : — (1) the non -recognition of the fact that 

 many lakes in the Northern Alps lie in longitudinal valleys ; (2} 

 the omission, in the discussion of the relation of valleys to lines of 

 fracture, of the consideration of anticlinal lines of fracture, which 

 can be shown to be very common in the Alps ; (3) the illogical 

 inference from conditions existing in crystalline metamorphosed rocks 

 as to what could or could not occur in the stratified sedimentary de- 

 posits of the Alps, among which the Alpine lakes chiefly occur-, (4) 

 the rejection of the hypothesis of subsidence on the mere ground of 

 the number of instances. The author proceeded to show that the 

 lakes of the Northern Alps are found, as a rule, just among those 

 strata where subsidence would be most likely to occur. In this 

 way it was shown that we are not shut up, by Prof. Ramsay's reason- 

 ing, to the hypothesis of glacial excavation. 



Further, other agencies than those discussed by Prof. Ramsay 

 may have cooperated to form lakes, such as : — 



(a) Alterations in the relative levels of different parts of a floor 

 of a valley, connected with movements of parts of a mountain- 

 system on a large scale. The effects of (1) lines of flexure crossing 

 older lines of valley-erosion, (2) of lateral thrusts closing in a 

 valley (partly), were here considered. 



(b) Upthrust of the more yielding strata (as in the " creeps " of 

 coal-mines) by resolution of forces due to pressure of the mountain- 

 masses at the side of a valley. 



(c) The dead weight of the huge glaciers which filled the Alpine 

 valleys, and crushed in the floor, in places where extensive under- 

 ground erosion had gone on in preglacial times. 



(d) The partial damming up of valleys, (1) by diluvial detritus, 

 (2) by moraines, (3) by Bergsturze (recently investigated by Prof. 

 Heim of Zurich). 



(e) Faults. 



(f) Chemical solution, by Alpine waters derived from the melting 

 of the snow, which has undergone long exposure to the atmosphere. 



It was shown that the very situation of the great majority of the 

 lakes of the Northern Alps is distinctly favourable to the operation 

 of one or more of these agencies. The Konigsee was mentioned 



Phil. Mag. S. 5. Vol. 15. No. 91. Jan 1883. F 



