CHARACTERISTICS AND DISTRIBUTION OF LAKES 593 
this has led to the formation of lakes in the Upper Engadine has been 
already explained. In addition to these alterations in the river- 
system, recent changes of level are said to have diverted the courses of 
some of the rivers, and to have drowned parts of their valleys. The dams 
due to river-cones and glacial moraines have had the same effect. In 
general, the rivers follow the original folds of the strata, or cut across 
them at right angles, and in the latter case it is most probable that the 
river is older than the folds, and cut through them as they rose. 
Lakes may have existed there for a time, but as the ridges were cut 
down the lakes were then drained. The valley of the Rhine above 
Martigny, and the valley of the Rhone above Chur, mark the sites 
of such temporary lakes. 
According to Heim,^ the Alps were formerly higher than they are 
at present, and the rivers cut out wide valleys at that time. Later, 
the Alps sunk as a whole from 200 to 500 metres (650 to 1640 feet), 
and by this sinking part of the valleys M^ere drowned and lakes were 
formed. Proof of this sinking is found in the old terraces of many of 
the rivers, which run in the opposite direction to the present course of 
the rivers, in the filling up of the principal valleys with gravel, and 
in a bending in the Molasse which can be followed along the whole 
northern border. This view is supported by Aeppli and by Romer, 
and also by recent researches made in the Alpine border lakes by 
Dr E. Gogarten. On the other hand, Penck and Bruckner hold the 
theory that these lakes can be explained bv glacial erosion, and that 
there is no evidence of subsidence. 
The Upper Rhine is generally stated to have its source in the 
small lakes, Siarra and Toma. 
Lake of Constance (or Bodensee) is the first large lake in its 
course, and lies at an elevation of about 1300 feet above sea-level. It 
has an area of 208 square miles, and is 40 miles in length ; the maximum 
depth is 827 feet, and bhe mean depth 295 feet. The volume of water 
is estimated at 1,711,000 million cubic feet. At its west end it is 
dammed up to a certain height by the deposits of the ancient Rhine 
glacier, but this would not account for more than, say, a quarter of 
its depth. Penck ^ considers it a rock-basin due to changes in relative 
levels or to excavation by the glacier. 
Below the Lake of Constance the course of the Rhine gives 
indications of being comparatively recent, and is interrupted by 
bars of rock, one of these bars causing the magnificent fall of SchafF- 
hausen and regulating the height of the Lake of Constance, which 
1 Albert Heim, " Geologische Nachlese," No. 1, "Die Entsteliimg der alpinen 
Rand-Seen," Vierteljahrsschr. naturforsch. Ges. Zurich, vol. xxxix. p. 1 (sep.), 1894. 
2 Die Alpen im Eiszeitalter, vol. ii. p. 537, Leipzig, 1909. 
^ Cited by Lubbock, ojj. cit., p. 414. 
38 
