452 Dr. Du Riche Preller—The Engadine Lakes. 
the river at Sils, forming the Sils lake, while this, the largest of the 
Engadine lakes, will at no distant time be itself divided into two by 
the débris-cone of the Val Fedo torrent, which cone is gradually 
stretching across to the rocky spur on the other side. The next 
two lakes, that of Silvaplana and Campfer, were originally one, 
being formed by the deposits of St. Moritz torrent at Campfer, and 
were subsequently divided by the Julier torrent at Silvaplana. The 
St. Moritz lake alone presents somewhat different conditions, the 
bar being in this case not alluvial but older deposit rising above 
the lake level to a height of about 500 feet, through which the river 
has cut as yet only a narrow channel or rapid of one kilometre in 
length, having a total fall of 43 metres or 4:3 per cent. viz. ten 
times the fall and mechanical energy of the upper course. But it 
is only near Samaden that the Inn, by the addition of the Bernina 
and Val Roseg torrents, having a drainage area of 200 square 
kilometres and a volume of 13 cubic metres or tons per minute 
becomes a true Alpine river and then attains sufficient volume and 
fall (22 cubic metres or tons per minute) to cut through and wash 
away the lateral deposits, to exert its erosive energy to its full 
extent, and thus to prevent the formation of lakes further down the 
valley. 
The hydrographic changes brought about, in the first instance, by 
the subsidence or dislocation of the old divide of the Inn and 
Bargaglia systems, and by the consequent deflections to the south of 
the original Inn sources, are the more striking when we consider the 
enormous difference between the fall of the two river systems North 
and South of the Alps respectively. The entire course of the Inn 
from Maloja (1810 metres) to its confluence with the Danube at 
Passau (290 metres), where in volume it greatly exceeds the latter, 
is 400 kilometres or about 250 miles, the average fall being there- 
fore at the rate of 0-4 per cent., whilst in the Upper Engadine from 
Maloja to Samaden, a distance of about 16 miles, the fall is 
100 metres, or 0:4 per cent., viz. not above the average. The Meira, 
on the other hand, has from Casaccia (1460 metres) to Chiavenna 
(317 metres) in a distance of 22 kilometres or 14 miles a fall of 
no less than 1143 metres or 5°5 per cent., viz. more than ten times 
kilometres (six square miles). Taking the rainfall in those Alpine valleys at 
2-5 metres per annum, less 25 per cent. for absorption and evaporation, or in round 
figures at 2 metres (6°56 feet), the quantity of water of the three drainage areas 
respectively worked out as follows: 
isin, Cullen, ee = 438 cub. metres or 15,460 cub. ft. per min. 
Albigna, 365 x 24 x 60 
Up. Engadine lakes, Se er As “F 18,820 ,, ue 
Inn torrent, 6 cee AAEM G OMe thir 33 2,440 5, 45 
The old Inn carried therefore, at the present outflow of the St. Moritz lake, about 
1000 cubic metres or tons per minute, which quantity the deflection of the Meira, 
Orlegna and Albigna reduced to about one half, whilst the present Inn at Maloja 
only carries about one-sixth of the volume of the old river, the erosive power being 
reduced in the same proportion. 
