Sigaov B. Gastaldi on the Effects of Glacier -erosion. 235 



to admit of the supposition that a great glacier, coming from the 

 south, has passed over it to excavate the lake ; yet the Attersee, 

 in a position least favourable to glacial action, is the largest and 

 deepest lake in the Salzkammergut. The head of the valley in 

 which these lakes lie is really among low hills, in the direction of 

 the Austro-Bavarian plain. 



The Traunsee was shown to give no evidence in favour of a theory 

 of glacial erosion. 



Since, then, these lakes either had at their heads preglaeial cirques 

 (the very existence of which was incompatible with much erosive 

 power on the part of a glacier), or were beneath sharp and not 

 greatly elevated ridges of rock, the author concluded that they had 

 not been excavated primarily by glaciers. 



He considered a far more probable explanation to be, that the 

 greater lake-basins were parts of ordinary valleys, excavated by rain 

 and rivers, the beds of which had undergone disturbances after the 

 valley had assumed approximately its present contour. He showed 

 that the lakes were in most cases maintained at their present level 

 by drift, — and that while in a region so subject to slight disturbances 

 as the Alps positive evidence for his theory would be almost impos- 

 sible to obtain, no lake offered any against it, and one, the Konig- 

 see, was very favourable to it. 



2. " On the Effects of Glacier-erosion in Alpine Valleys." By 

 Signor B. Gastaldi. 



The author described the occurrence in the valley of the Lanzo 

 and other Alpine valleys, at heights between 2000 and 3000 metres 

 (6700 and 10,000 feet), of large eirques, c in two of which, in the valley 

 Sauze de Cesanne, the bottom was occupied in the autumn by gla- 

 ciers reduced to their smallest dimensions. The author noticed the 

 various rocks in which these cirques were cut, and expressed his 

 opinion that they are the beds formerly occupied by glaciers, the 

 power of which to excavate even comparatively hard rocks, such as 

 felspathic, amphibolite-, and chlorite-schists, he considered to be 

 proved. 



The author then referred to the mouths of the Alpine valleys 

 opening upon the plain, which he described as being generally very 

 narrow in proportion to their length, width, and orographical im- 

 portance ; and he pointed out that in the case of the valley of the 

 Stura, at any rate, the outlet of the valley has been cut out by the 

 river. This peculiarity he accounts for by the fact that whilst the 

 calcareous and felspathic rocks are easily disintegrated by atmo- 

 spheric action, certain other rocks, such as the amphibolites, diorites, 

 syenites, amphibolite-schists, euphotides, serpentines, &c, resist 

 atmospheric denudation ; and he indicated the peculiar distribution 

 of these rocks in the region under consideration, by reason of which 

 portions of them occupied the points which are now the mouths of 

 the valleys. 



