1882 .] 
331 
[Davis. 
and converted for a time (of which the present epoch is a part) 
into marginal lakes . 1 
For the Reuss, it is probable that its early course lay in contin- 
uation with the upper part of Lake Lucerne (Urner See), east 
of the Rigi, into the troughs of Lakes Zug and Zurich; a land- 
slide from the Rossberg turned it westward by a longitudinal 
valley till it joined the Aa, and the two streams flowing north- 
ward together were converted into a lake by foldings in the 
neighborhood of Lucerne . 2 This last change had a marked effect 
on the course of the Kleine Emmen also ; this stream rises north 
of Interlaken and has a well preserved old valley across the Plat- 
eau to the Aar at Aarburg, but now abandons its old course at 
Wiggern, and turns sharply round to the east, following a trough 
which carries it to the Reuss below Lucerne . 3 
Changes similar to these are appealed to by Favre to explain the 
origin of Lake Geneva 4 and by Rtitimeyer to account for several 
of the lakes of Northern Switzerland , 5 but their arguments are 
more geological than can be properly introduced here. 
It is objected to the above explanation that, in the case of 
Lake Lucerne for example , 6 the material eroded from the neigh- 
boring mountains should have long ago filled the basin ; but if we 
accept the well-reasoned conclusions of Heim and Rtitimeyer, 
it will be apparent that the region about the lake was eroded 
much into its present form before the outer post-miocene folding 
changed the valley into a basin. 
That several of these lakes are submerged valleys of erosion is 
made the more probable by finding the form of their cross-section 
agreeing closely with that of a river trough, after a long period of 
lateral cutting with but little deepening has given it a flat bot- 
1 Heim, Mechanismu der Gebirgsbildung, 1878, ii, 228-230. 
2 Heim, op. cit., i. 316. 
3 Shown distinctly on the Dufour map of Switzerland, sheet viii. 
4 Recherches G£ol., I, 212. 
6 Ueber Thai- und Seebildung, 58. 
6 A. Geikie, On the Geol. Structure of some Alpine Lake-basins, Edinb. Roy. Soc. 
Proc., xii, 1869, 33-34. 
