86 LITBRATCRE ON TORRENTS, 



dykes are much better suited for the enclosure of this small water-course. 

 And on all the lower channel of the Linth, they have little by little replaced 

 with these the stakes wherever these were not absolutely necessary." 



M. Culmann then reports in detail in regard to the location and construction 

 of bridges j and on the phenomena and effects of glaciers, torrents, avalanches, 

 and landslips. 



The former subject is of local importance ; and the information communi- 

 cated may be utilized, to some extent, by any employed in making surveys 

 for roads and bridges ; but in every case local circumstances have such an 

 effect in determining operations that it is deemed unnecessary to cite the 

 views advanced. With regard to glaciers, torrents, avalanches, and land- 

 slips, the case may seem to be similar. But avalanches, at least, are not 

 coniined to Alpine regions ; and though woods may prevent the formation 

 of a landslip, they cannot arrest its progress when once in motion. There 

 is not a little in the graphic details of engineering operations given by 

 M. Culmann in this chapter of his work which commands attention and 

 illustrates the importance of the work. 



" Torrents issuing from glaciers," says M. Cteanne, " are numerous in 

 Switzerland ; they are subject to formidable dihdcles, or outbursts of water, 

 when the glacier in its movements of going and coming, after having 

 dammed up some secondary valley, gives free passage all at once to its 

 waters. To prevent such evils is for the engineer a formidable undertaking, 

 and a difficult problem. How contend against a glacier ? What physical 

 force can he bring against the mass which is being unceasingly renewed by 

 the ever recurring winters, and which, making use of the hardest rocks, trans- 

 porting blocks of stupendous size by a movement almost imperceptible, 

 would annihilate the most irresistible work of man ? Here are two cases 

 reported in which a simple idea sufficed to vanquish the inert Colossus : 



" The glacier d'Aletsh, an affluent of the Ehine (Valais), dammed up a 

 small lateral valley, situated behind the Eggishchorn, and created thus the 

 lake of Mserjelen. ' This lake,' says M. Agassiz, in his Mudes sur les Glaciers, 

 ' was formerly more extensive than it is now ; and when it happened that 

 the melting of the snow and ice became excessive, it would often happen 

 that the whole of this body of water would with violence eat away an outlet 

 under the glacier, and occasion the greatest destructive ravages in the 

 bottom of the valley. To obviate this they dug, in the direction of the 

 glacier of Viesch, an artificial channel to this lake, which could no longer 

 rise above the level of its orifice. The ice did not rest immediately on the 

 water ; there was, on the contrary, between the bottom of the glacier and 

 the surface of the water a space of some centimetres, perhaps an inch or 

 two, occasioned by the temperature of the lake being always during summer 

 higher than that of the glacier. By means of this space, enormous blocks 

 of ice often detach themselves and float on the surface of the lake, imitating 

 exactly the floating icebergs of northern regions.' 



" But the most characteristic example is that furnished by the glacier of 

 Gifetroz — the assault made against which is somewhat dramatic, and 

 exceedingly interesting : 



" At the bottom of the valley of Bagnes, one of the branches of the Drause, 

 at sixteen kilometres, or about twelve miles from Chables, there rises 

 vertically a high wall of rocks, surmounted by the glacier of Gi^troz. The 

 moving mass protrudes itself, projects beyond the support, and falls at the 



