1873.] BONNEY ALPINE LAKES. 391 



these lakes being only a bank of drift, which has mainly descended 

 from the low hills on the north ; so that they are practically one 

 lake. It is obvious, then, that these three lakes occupy a connected 

 system of valleys, one parallel with, and two perpendicular to, the 

 general strike of the strata ; for the Atter See crosses in reverse order 

 from the base of the limestone escarpment the same rolling lines of 

 hills that are intersected by the valley occupied by the Zeller and 

 upper Mondsee, until they sink down into the great plain. 

 Supposing, then, for a moment this system of valleys traced out by 

 other causes, let us see how far it is possible to explain the lake- 

 basins by glacial erosion. 



Excepting that which brings the waters of the Fuschelsee, only 

 one valley of any importance leads to these lakes, viz. that through 

 which a road passes from Ischl to Weissenbach at the S.E. corner of 

 the Atter See. Any one who has travelled along this must admit 

 that it cannot have been traversed by any very large ice-stream, 

 whether this had crossed the low pass from the Traun valley or had 

 descended from the recesses of the Hoch-Lecken and Hbllen Gebirge. 

 It is impossible to suppose that glaciers could have been produced 

 among the low hills about the Zeller See, or on the terraced scarp of 

 the Schaff berg, capable of ploughing out this lake-system ; can we 

 then adopt the only remaining hypothesis, and suppose that a large 

 glacier descended from the south at right angles to the Wolfganger 

 See, and, after scooping out that lake, passed either on the east or on 

 both sides of the Schaffberg, and ploughed out the troughs above 

 described ? The occurrence of the little tarn of the Schwarzen See * 

 on the former of these lines might at first sight seem to favour this 

 hypothesis ; but the contours of the neighbouring hills are far from 

 being such as we should expect (being sharp ridges) had they been 

 subjected to such enormous pressure as would be exercised by a 

 glacier capable of grinding out the deep Atter See. No glacier can 

 have passed to the west of the Schaffberg ; for the basin of the Wolf- 

 ganger See is separated from the Mondsee by a ridge (of Dachstein- 

 kalk) which, though of no great height, is as sharp and unworn by 

 ice as the top of the Schaffberg itself. Yet formerly this ridge, 

 when the waters of the lakes stood higher, was the only barrier 

 between them, since a level delta extends up to it on the north from 

 Schorflung on the Mondsee, and on the south it is washed by the 

 Kroten See, a little tarn at the head of what has evidently been an 

 arm of the Wolfganger See, now a shelving expanse of drift. 



The remaining lake in this district, the Traunseef is situated 

 about 9 1 miles below Ischl, in the valley of the Traun ; but the true 

 head of the lake-basin is nearly 4 miles nearer that town, the 

 intervening space being a delta chiefly formed by affluents from the 



* Rather more than a mile long (N.E. to S.W.), 57 yards wide, 168 feet 

 deep, the deepest soundings being in the middle. Height above sea 1880 feet 

 (Ball, Alpine Guide). Wallmann gives it 1159 feet, which is evidently a 

 misprint, a probable correction in the number given (in Vienna feet) would 

 make it 1816 — that is, 65 feet above the Wolfganger See. 



t Nearly 8 miles long, 1 jj wide, 1336 feet above the sea, 626 feet deep. 



