Dr. Du Riche Preller—The Engadine Lakes. 451 
hypothesis appears untenable, when it is considered that as long as 
the divide of Vicosoprano existed, the principal river of the then 
Bargaglia valley and its tributaries must have been very insignifi- 
cant, and their erosive power, in spite of their great fall, quite 
insufficient to excavate backwards, even to the Albigna, a mountain 
barrier 6600 feet in vertical depth and composed, like the massifs 
of the Bargaglia and Engadine ranges generally, of granitic gneiss, 
and hornblende schists. The deflection of the Meira, Albigna, and 
Olegna from their former course can only have been produced in the 
first instance by a subsidence of the old divide, whereby a basin or 
trough was formed between Vicosoprano and Maloja, and the three 
powerful torrents now turning to the south, and gaining consider- 
ably in fall were able to erode the remainder of the divide at 
Vicosoprano and form the Bargaglia valley of the present day. The 
subsidence and consequent formation of the Casaccia trough is 
attested not only by the general configuration of that trough and by 
the defile of Vicosoprano, but also by the quasi-perpendicular wall 
or drop of 800 feet immediately below Maloja, no less than by the 
Albigna which in its upper course of about a mile, viz. before its 
deflection to the south, now falls from 2000 to 1200 metres, equal 
to a fall of no less than 346 per cent. or more than ten times its old 
fall to the Engadine. The erosive action of the rivers and torrents 
below as well as above Vicosoprano was therefore only the secondary 
cause, the primary cause being a subsidence; and this explanation 
tallies, moreover, remarkably well with Professor Heim’s own and 
latest views with regard to the origin of the principal Alpine lakes 
as the effect of a subsidence of the massif of the Alps between the 
first and second glacial epochs, to which views I propose to refer in 
a future communication. 
The effect of the deflection of the original sources of the Inn 
system to the south, by which the Upper Engadine valley was 
deprived of its principal agents of erosion, was the gradual forma- 
tion of the Sils, Silvaplana, Campfer, and St. Moritz lakes. From 
a powerful Alpine river, the Inn at Maloja was reduced to a small 
torrent which had neither sufficient volume nor sufficient fall to 
wash out and carry away the deposits brought down by lateral 
torrents between Maloja and Camadon; hence these deposits filled 
and raised its bed, and thus the lakes whose average depth is about 
350 feet were formed by the weakened river being banked up at 
various points. Thus the deposits of the Val Fex torrent banked 
phorical phraseology in which he delights, that distinguished geologist speaks of the 
“tremendous fight between the Meira and the Inn which ended not only in the 
complete discomfiture of the latter but also in the Orlegna and Albigna forsaking » 
their old allegiance.” It is difficult to see how there could be a fight, because —to 
follow up the metaphor—the Inn was simply a passive looker-on, and the Meira and 
the other two rivers turned naturally to the south when an opening was made for 
them, giving them a greater fall. 
! From measurements made by the writer the combined drainage area of the 
Meira, Orlegna, and Albigna within the old (Vicosoprano) divide, is about 120 square 
kilometres (44 square miles); that of the four lakes from the present (Maloja) 
divide to the lower end of St. Moritz lake is 140 square kilometres (51 square miles) ; 
and that of the present Inn torrent rising in the lake Lunghino, is 16 square 
