ORIGIN OF V ALLEY- LAKES, 77 



bance of the strata of the region may produce such alterations in the 

 relative levels of different parts of the valley as to bring the floor of 

 the valley at some points to a higher level than the floor of the 

 valley nearer to its head. It is no drawing upon the imagination 

 to say that such movements have occurred on a large scale in the 

 Alps since the older lines of valley were eroded by water-action. 

 To mention one fact only, the changes of level of the European con- 

 tinent which brought the shores of the continent so far south as to 

 allow the southerly drifting icebergs from Scandinavia to deposit 

 their erratic blocks as far inland as Bonn, Westphalia, Thuringia, 

 Saxony, and Moscow* could hardly have happened during Quater- 

 nary times, and been reversed, without some considerable squeezing 

 and consequent disturbances of the strata of the Alps, such as we 

 observe today on such a gigantic scale. 



I take it, then, that many of the lines of flexure which have been 

 before referred to as abounding in the stratified Alpine deposits are 

 of comparatively recent date. The effect of such lines of flexure 

 occurring transversely to the older lines of valley- erosion would be 

 to form hollows, which must get filled with water from the surface- 

 drainage of the valley. This has been already pointed out by Prof. 

 Bonneyf ; and I may perhaps illustrate the principle more fully than 

 he has done from the example of the Lake of Hallstadt. This beautiful 

 lake lies in a north-to-south valley, and is one of some half a dozen 

 lakes which lie in the line of the river Traun. The stratigraphy of the 

 Hallstadt basin may be understood readily from the accompanying 

 sketch (p. 78), which was made on the spot, not from a cursory glance, 

 but during a stay of more than a fortnight in the vicinity of Hallstadt. 

 It of course represents the face of the mountain on the western side 

 of the lake. The strata of the Sarstein massif on the eastern side 

 show a corresponding synclinal arrangement. The line of anticlinal 

 flexure, which is recorded in the dip of the strata from the Gosau 

 Schlucht, having been formed in comparatively recent times, has 

 produced so much of the Hallstadt lake as lies in a true rock-basin. 

 The lake owes, however, a considerable portion of its depth to the 

 diluvial detritus which has been brought into the Traun valley 

 from a valley on the eastern side, and has dammed up the valley 

 from Steg in the direction towards Ischl. The section represents 

 a thickness of strata of over 4000 feet, entirely of Triassic age. 

 About midway between the two gorges the strata above the pine- 

 forests are highly contorted ; and beyond them lie the contorted 

 upper Dachstein strata. 



It is worthy of remark that such changes of level as are here re- 

 ferred to are not so distinctly recorded as are many similar changes 

 which are known to have occurred in mountain-regions contiguous 

 to the sea (e. g. in Norway, in South America, and in New Zealand), 

 where the mean sea-level serves as a datum-line from which to esti- 

 mate their extent %. 



* Credner, El. der Geol. p. 651. 



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



\ Vide Credner, ibid. pp. 169, 170. 



