Davis.] 
356 
[January 18 , 
first examine the possible explanations, and second, see how far 
these agree with the facts : it is to be regretted that the result of 
this inquiry must remain indeterminate as to the quantitative 
relations of certain causes. 
J 
The essential features of these lakes may be represented by the 
above diagram : there is the mountain-mass of the Alps, J C, 
to the north of a great depression, C H K, the valley of the Po. 
Eroded detritus has been carried from the former to the latter 
along valleys without lakes, ABC, and along valleys with lakes, 
AED C. In the former there is nothing peculiar ; but in the 
latter, how does it happen that the lakes, E D C, are still empty 
while the plain beyond has been filled to a level, C G K? The 
depth of D below C G is reported to be in Lago Maggiore more 
than two thousand feet. 1 The barrier F C is made to an unknown 
depth of deposits similar to those at G, aided by a superposed 
moraine of great size ; it has not been shown to consist of rock. 
1. We may suppose the lake-valley had the slojte ABC dur- 
ing the filling of the depression CHKG; a subsequent folding 
would convert, ABC into A E I) C, and E D C would become a 
lake. This has been suggested, 2 but cannot here be so well demon- 
strated as for the lakes at the northern margin of the Alps. So far 
as it is true, it would throw the basins into the warped valley spe- 
cies. We say nothing of faults or fissures, for there is no sufficient 
evidence to show that they have been of importance in making 
the valleys. 
2. The original line, ABC, may have been, as suggested by 
Ramsay, cut down to A E D C by a glacier, whose former occu- 
pation of the valley is well proven ; but this requires the admis- 
sion of an enormous erosive power for glacial ice, which we can- 
1 It is very possible this depth may be exaggerated, as the measures of many other 
lakes have been. See Simony, loc. cit. 538. 
2 Lyell and Bonney as above, A. 4. 
