386 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [-^pril 9, 



which above the Obersee form an almost unbroken precipice at least 



1000 feet high. Assuming the glacier to have started at a height of 



about 6500 feet above the sea, or 



4500 feet above the lake, and to 



have had a course (measured on the 



flat) of rather more than 2 miles 



(say 12,500 feet), it then, after 



descending a bed the average slope 



of which would be given by the 



line A B in the diagram, suddenly " 12500 ft. 



digs out the cliff A C, after which 



the average slope of the basin can hardly exceed 3-5 in the 100. 



Surely a configuration like this is mechanically impossible ? 



If, however, the valley be regarded apart from the lake, it 

 presents no more difficulty to a" rain and river " origin than most 

 others in the Alps, being a gorge-like glen with a cirque at the 

 head formed by the union of several streamlets from various slopes 

 and upland recesses. When, however, we regard the lake, we must 

 account, if possible, for the fact that its bottom at the lowest point is 

 about 500 feet below the true bed of the valley at Berchtesgaden, or 

 possibly even at its north extremity. This we shall attempt to do 

 in a later part of the paper. 



The Hallstlidter See* is hardly less remarkable than the Konig- 

 see for the extreme steepness of its walls. The Sarstein range 

 (6558 feet) hems it in on the east, which presents a steep curtain of 

 pine forest surmounted by a continuous face of limestone rock. On 

 the west the mountains are more broken ; but still they rise very 

 abruptly for from 1000 feet to 2000 feet above the lake. This 

 extraordinary trough at the first sight seems not unfavourable to 

 the glacier-erosion hypothesis. 



To the S.S.W. is the Dachstein massif, which still gives rise to 

 considerable glaciers (9845 feet). The lowest part of the lake- 

 basin is probably not very much less than 600 feet below the rocky 

 bed of the Traun at Lauffen, to which place, about 5 miles distant 

 from the present end, its waters doubtless once extended. A closer 

 examination, however, suggests grave difficulties. 



First, the true plan of the lake-basin is not a simple trough 

 pointing at the Dachstein, but a J, its head being formed by two 

 well-marked valleys (the Traunthal and the Wildbachthal), each 

 enclosed by precipitous walls, and running E. and W., up which it 

 is evident that the lake once extended. The Traun enters the 

 former arm from the N. by a ^-shaped glen. The Wildbach 

 torrent rushes into the latter down a magnificent and inaccessible 

 gorge. If, then, the lake is a glacier-basin, one ice-stream must 

 have come down from the E., another from the W., and the two 

 when united have turned to the 1ST. The mountains, however, at 

 the heads of these glens are much lower than the Dachstein, and 

 are not likely to have produced glaciers of exceptional size. If the 



* Bather more than 5 miles long and less than 14 broad, extending from S.E. to 

 N.W. 1769 feet above the sea (v. Buch). Upper" part 612, lower 138 feet deep 



