ON LAKE BASINS. 
591 
numerous feeders, and several of them are connected by narrow 
clefts occupied by streams. The Lago Maggiore is 2,600 feet 
deep. All come down from the north, being nearly at right 
angies to the general east and west direction of the great 
mountain chain. All are narrow compared to then* length, but 
their width is enormously too great to be due to mere mechanical 
disruption. The Lake of Geneva, on the other hand, ranges 
east and west, on a parallel to the mountain chain. It is a 
lake within the great area of elevation, on the north side of 
the high Alpine chain, and within the plateau of Switzerland. 
A score of lakes of the same general character are scooped out 
of the soft tertiary sandstones of the valley of Switzerland. 
But all who are familiar with Switzerland will remember the 
lofty mountain wall of hard rock to the south of the Lake of 
Geneva, the corresponding wall of the Jura, enclosing the Lake 
of hTeufchatel, the peculiar and well-marked vertical rocks that 
shut in many parts of the Lake of the Four Cantons, and the 
mountain sides that shut in the little Lake of Thun. I speak 
from recollection, and the memories of Alpine travellers will 
supply a score of similar illustrations. There is equal evidence 
of original disruption and subsequent degradation and erosion, 
both on a g’rand scale, neither of them sufficient alone to pro- 
duce the results observable, but both combining. Thus the 
disruption has been followed by long*- continued and even violent 
erosion, partly by water, and afterwards by ice. ' The result is 
seen in the mixed disturbance by mechanical violence and 
denudation, by the paring away of vast quantities of material 
once accumulated over the rocks at present forming the moun- 
tain tops. The Lago Maggiore is not very much above the 
level of the sea, and its depth is great enough to justify the 
assumption that some cause in addition to erosion has acted. 
The Lake of Geneva is scarcely excavated to the sea level. But 
there must have been some depression in all these and similar 
cases in addition to the vast elevation, which has not only lifted 
up the sea bottom to the height of fifteen thousand feet in the 
Alps, eighteen thousand in the Caucasus, and twenty-eight 
thousand in the Himalayas. Probably the difference of height 
between the Alps and the Himalayas — equivalent to a thick- 
ness of thirteen thousand feet of strata — may have been re- 
moved bv this water action. But this has not been done 
«/ 
rapidly, and it has not been done equally over the whole area. 
Parts that were soft have been pared only from the surface. 
Similar soft rocks beneath the surface have been undermined. 
Hard parts have been occasionally left. Some of the fragments 
of hard rock have helped to destro}^ long ledges of strata. 
Thus it is that the history of lake basins is not quite so 
simple as may at first appear. There are many that, having 
been formed and filled during the action of some erosive force. 
