378 DR. C. S. DU RICHE PRELLER ON ELTTVIO-GLACIAL [Aug. 1 89 5, 



probably reached to the banks of the present Lake of Zug ; while the 

 gravel-deposits in the Lorze Valley and its neighbourhood are the 

 results of banking up by the main glacier of the Reuss, which, flowing 

 more or less at right angles, constituted a formidable barrier. Hence 

 the Lorze Valley-deposit, formed outside the main river, is essentially 

 a debris-cone superposed on the old delta. 



IV. Deposits near the Lake of Tht/n. 



Hardly less remarkable than the deposits near the Lake of Zug 

 are tbose in the Kander Valley near the lower end of the Lake of 

 Thun. This last-named interesting, but complex district has been 

 dealt with by various Swiss geologists, notably by Studer as earlv 

 as 1825, 1834, and in 1871, 1 by Bachmann in 1870 and 1876, 2 and 

 quite recently (namely in 1892) in a very able memoir by Dr. Zol- 

 linger of Bale. 3 As is seen from the plan of the district (figs. 8 and 

 9, pp. 379, 380), the rivers Kander and Simme, both of which rise in 

 the Bernese Oberland and have a combined drainage-area and volume 

 about equal to those of the Aare at the upper end of the Lake of 

 Thun, have their confluence about 2 miles from the present lake, 

 and discharge into the latter, about midway between Thun and 

 Spiez. Up to the year 1714 the Kander, reinforced by the 

 Simme, flowed from Glutsch to the left, through the present 

 Glutsch Valley, and discharged, not into the lake, but into the 

 river Aare just below Thun. The large volume and deposit carried 

 by the Kander naturally banked up the river Aare, and with the view 

 of removing the danger of frequent inundations, the Kander was, in 

 1714, artificially deflected from the Glutsch Valley into the lake by 

 a tunnel near Strattlingen cut through the intervening gravel and 

 moraine-ridge. 4 The considerably increased fall (1 in 20) and 

 shorter flow of the new outlet naturally caused not only the rapid 

 formation of a delta at the outflow into the lake, but the gradual 

 falling-in of the tunnel, and the deepening of the river-bed. This latter 

 is now 150 feet below the original artificial level of 1714, although 

 the process of backward erosion has gradually equalized the varia- 

 tions of fall between the confluence and the lake as well as the rate 

 of deposition at the delta. 5 



1 ' Beytrage zu einer Monographie der Molasse,' Berne, 1825; 'Geologic 

 d. westl. Schweizer Alpen,' Heidelberg & Leipzig, 1834; 'Zur Geologie des 

 Ralliger Gebirges,' 1871. 



2 ' Kander,' 1 870 ; ' Geologisches iiber die Umgebung von Thun,' Jabrb. 

 Schweiz. Alpenclub, vol. xi. (1876) p. 371. 



3 ' Zwei I lussverschiebungen Bern. Oberland,' 1892. 



4 The river Liitscbinen, which formed the delta of Interlaken, now sepa- 

 rating the lakes of Brienz and Thun, was similarly diverted into the former lake 

 as early as 1257. Another artificial deflection was that of the Linth into the 

 Lake of Wallen, in 1815. 



5 From the official measurements quoted by Dr. Zollinger, the rate of forma- 

 tion of this delta from 1714 to 1857, namely, in 143 years, is as follows : — 



1714 to 1716 = 3 years 

 1716 „ 1740 = 24 

 1740 „ 1777 = 37 

 1777 „ 1857 = 80 



20 hectares = 50 acres = 16 - 66 acres per annum. 



30 „ =75 „ = 3-12 „ „ 

 8 „ = 20 „ = 0-44 acre „ „ 

 7 „ = 17-5 „ = 0-22 „ „ 



Total 65 hectares = 162 - 5 acres in 143 years = mean 144 acre per annum. 



