Vol. 51.] AND INTJERGLACTAL DEPOSITS IN SWITZERLAND. 385 



As regards the duration of the two interglaeial periods in the 

 Alps, Dr. Zollinger endorses the generally accepted view that the 

 first of these periods was considerably longer than the second. By 

 calculating the amount of deposit formed by the river Simme, and 

 dividing this by the average annual amount of deposit by the Reuss 

 at its inflow into the Lake of Lucerne, according to Prof. Heim's 

 measurements, he arrives at the figure of 3000 years as the duration 

 of the second interglaeial period in the Kander Yalley. 1 The 

 approximate agreement of this figure with Heer's 2400 years for the 

 Pleistocene lignite-deposits in the North of Switzerland is, in his view, 

 more than accidental, that is, confirmatory of his own conclusions. 

 But it has already been shown that the fluvio-glacial conglomerates 

 of the Simme must be regarded as the product of the first glaciation, 

 and not as belonging to the second interglaeial period. Moreover, 

 the proper standard of comparison with Heer's computation would 

 be, not the gravels, but the Kander lignite-band, which would give 

 a very small fraction of 2400 years; and, lastly, Dr. Zollinger's 

 calculation, like all similar ones, takes no account of the enormously 

 enhanced depositing power of torrents and rivers when in flood. 



The same important factor is neglected when it is attempted to 

 fix the duration of the first interglaeial period. The assumption of 

 a much longer duration than that of the second interglaeial period 

 rests solely upon the enormous accumulations of gravel-conglomerate 

 in the lower Alpine valleys, pointing to a protracted process of erosion 

 in the upper valleys ; but it is much more likely that, more espe- 

 cially during the melting or receding of the glaciers, the rivers 

 were in flood much more frequently, and consequently the erosion 

 and deposition of material took place far more rapidly than in our 

 own day. For example, if we apply the present annual rate of 

 deposition by the river Linth (about 100 cubic metres of material 

 per square kilometre, or 160 cubic yards per square mile of drainage- 

 area) to the old Sihl deposit in the Lorze Valley, we arrive at the 

 manifestly extravagant figure of 60,000 years. 2 In order to reduce 

 it to 3000 years, or about the duration of the second period according 



1 Superficial area of Simme deposit = 6,000,000 sq. m. X 30 m. depth = 

 180,000,000 cub. m. Reuss drainage-area = 825 sq. kilom. ; annual deposit = 

 150,000 cub. m. Simme drainage-area = 600 sq. kilom. ; hence pro rata deposit 

 = 110,000 cub. m., less 50,000 cub. m. allowance for difference of fall and pre- 

 cipitation = 60,000 cub. m. Hence — ' , ' — = 3000 years. 



2 The Linth is a more adequate criterion than the Reuss. Upper drain- 

 age-area of Sihl = 200 sq. kilom. Linth drainage-area = 600 sq. kilom. ; 

 deposit (according to Dr. Biirkli's measurements) = 60,000 cub. m. per 

 annum. Hence Sihl deposit = 40,000 cub. m. per annum. Sihl deposit Lorze 

 Valley 6x4 kilom. = 24 sq. kilom. = 24,000,000 sq. m. X 100 m, 



depth = 2,400,000,000 cub. m. Hence % ^j^§^ = 120,000 years; 



2,400,000.000 flnnn _, ., . ' . . ,. 



0f . ,^. ^rr~ — "^00 years. Even the present Sihl carries during ordinary 



high water in summer 400 cub. m. of water per second, or about 40 times more 

 than its average ; and torrents, when in flood, are known to carry as much as 

 4000 times more than their average volume. 



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