CONSEQUENCES OF DRAINING LAKES. 419 



with wholly unexpected evils, as, for example, in the case of Bar- 

 ton Pond, in Yermont, and in that of a lake near Kagunda in 

 Sweden, already mentioned on a former page. Another still less 

 obvious consequence of the withdrawal of the waters has occasion- 

 ally been observed in these operations. The hydrostatic force with 

 which the water, in virtue of its specific gravity, presses against 

 the banks that confine it, has a tendency to sustain them when- 

 ever their composition and texture are not such as to expose them 

 to softening and dissolution by the infiltration of the water. If, 

 then, the slope of the banks is considerable, or if the earth of which 

 they are composed rests on a smooth and slippery stratum inchn- 

 ing towards the bed of the lake, they are liable to fall or shde for- 

 ward 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 Unterwal- 

 den, in Switzerland, was lowered by driving a tunnel about a 

 quarter of a mile long through the narrow ridge, called the Kais- 

 erstuhl, 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 Lungern Avas 

 thought to be in no small danger.* 



nected and the common level of all of them lowered about four feet. The 

 works in operation in 1871 were expected to produce, in the course of the year 

 1874, a further depression of four feet, and recover for agricultural use more 

 than twelve thousand acres of fertile soil. A part of the plan of the works 

 referred to is a canal for turning the river Aar into the Lake of Bienne, out 

 of which it will flow again by a new channel cut at a depth which will con- 

 siderably lower the surface of the Lake. In excavating the canal in the course 

 of 1874, the workman struck into an ancient Roman tunnel previously un- 

 known, which was apparently constructed for the purpose of partially drain- 

 ing the Lake of Bienne, the surface of which originally stood at a higher level 

 than in modern times, into the Aar. The timnel, which is about half a mile 

 in length, lies almost exactly in the line of the new canal, and will be destroyed 

 in the course of the excavations. Some suppose this tunnel to have been 

 pierced to serve as a common road. 



* In 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 Feriolo 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 



