MOUNTAIN LAKES. 433 
posed rests on a smooth and slippery stratum inclining towards 
the bed of the lake, they are lable to fall or slide forward 
when the mechanical support of the water is removed, and 
this sometimes happens on a considerable scale. A few years 
ago the surface of the Lake of Lungern, in the Canton of Un- 
terwalden, in Switzerland, was lowered by driving a tunnel 
about a quarter of a mile long through the narrow ridge, called 
the Kaiserstuhl, which forms a barrier at the north end of the 
basin. When the water was drawn off, the banks, which are 
steep, cracked and burst, several acres of ground slid down as 
low as the water receded, and even the whole village of Lun- 
gern was thought to be in no small danger.* 
Mountain Lakes. 
Other inconveniences of a very serious character have often 
resulted from the natural wearing down, or, much more fre- 
quently, the imprudent destruction, of the barriers which con- 
fine mountain lakes. In their natural condition, such basins 
serve both to receive and retain the rocks and other detritus 
brought down by the torrents which empty into them, and to 
check the impetus of the rushing waters by bringing them to 
* Jn the course of the year 1864 there were slides of the banks of the Lake 
of Como, and in one case the grounds of a villa near the water suffered a con- 
siderable displacement. More important slips occurred at Fesiolo on the 
shore of Lago Maggiore in 1867 and 1869, and on the Lake of Orta in 1868. 
These occurrences excited some apprehensions in regard to the possible effects 
of projects then under discussion for lowering the level of some of the Italian 
lakes, to obtain an increased supply of water for irrigation and as a mechani- 
cal power, but as it was not proposed to depress the surface below the lowest 
natural low-water level, there seems to have been little ground for the fears 
expressed. 
See, for important observations on the character and probable results of 
these projects, TAGLIASECCHI, WVostizie etc. dei Canali del? Alta Lombardia, 
Milano, 1871. 
Jacini says: ‘‘ A large proportion of the water of the lakes, instead of dis- 
charging itself by the Ticino, the Adda, the Oglio, the Mincio, filters through 
the silicious strata which underlie the hills, and follows subterranean chan- 
nels to the plain, where it collects in the fontanili, and being thence con- 
28 
