258 



TUE GEOLOGIST. 



from Faverges, at the head of the Lake of Annecy, across Savoy. It sepa- 

 rated Mont Yergi from the Mont Dorons, and the Dent d'Oche from the 

 Dent du Midi; then entered Switzerland, separating the Moleson from 

 the Diablerets ; passed on through the districts of Thun and Brientz, and, 

 dividing itself into two. caused the zigzagged form of the Lake of Lucerne. 

 The principal branch then passed between the high Sentis and the Glar- 

 nisch, and broke into confusion in the Tyrol. On the north side of this 

 trench the chalk beds were often vertical, or cast into repeated folds, of 

 which the escarpments were mostly turned away from the Alps ; but on 

 the south side of the trench, the Jurassic, Triassic, and Carboniferous beds, 

 though much distorted, showed a prevailing teudency to lean towards the 

 Alps, and turn their escarpments to the central chain. 



Both these systems of mountains are intersected by transverse valleys, 

 owing their origin, in the first instance, to a series of transverse curvilinear 

 fractures, which affect the forms even of every minor ridge, and produce 

 its principal ravines and boldest rocks, even where no distinctly-excavated 

 valleys exist. Thus, the Mont Yergi and the Aiguilles of Salouvre are 

 only fragmentary remains of a range of horizontal beds, once continuous, 

 but broken by this transverse system of curvilinear cleavage, and worn or 

 weathered into separate summits. 



The means of this ultimate sculpture or weathering were lastly to be 

 considered. 



III. Sculpture. — The final reductions of mountain form are owing either 

 to disintegration, or to the action of water, in the condition of rain, rivers, 

 or ice ; aided by frost and other circumstances of temperature and at- 

 mosphere. 



All important existing forms are owing to disintegration or the action 

 of water. That of ice had been curiously overrated. As an instrument 

 of sculpture, ice is much less powerful than water ; the apparently ener- 

 getic effects of it being merely the exponents of disintegration. A glacier 

 did not produce its moraine, but sustained and exposed the fragments 

 which fell on its surface, pulverizing these by keeping them in motion, but 

 producing very unimportant effects on the rock below ; the roundings and 

 striation produced by ice were superficial ; while a torrent penetrated into 

 every angle and cranny, undermining and wearing continually, and carry- 

 ing stones, at the lowest estimate, six hundred thousand times as fast as 

 the glacier. Had the quantity of rain which has fallen on Mont Blanc in 

 the form of snow (and descended in the ravines as ice) fallen as rain, and 

 descended in torrents, the ravines would have been much deeper than they 

 are now, and the glacier may so far be considered as exercising a protective 

 influence. But its power of carriage is unlimited, and when masses of 

 earth or rock are once loosened, the glacier carries them away, and exposes 

 fresh surfaces. Generalty, the work of water and ice is in mountain sur- 

 gery like that of lancet and sponge — one for incision, the other for ablu- 

 tion. "No excavation by ice was possible on a large scale, any more than 

 by a stream of honey ; and its various actions, with their limitations, were 

 only to be understood by keeping always clearly in view the great law of 

 its motion as a viscous substance, determined by Professor James Forbes. 



The existing forms of the Alps are, therefore, traceable chiefly to denu- 

 dation as the} r rose from the sea, followed by more or less violent aqueous 

 action, partly arrested during the glacial periods, while the produced di- 

 luvium was carried away into the valley of the Bhine or into the North 

 Sea. One veiy important result of denudation had not yet been sufficiently 

 regarded ; namely, that when portions of a thick bed (as the Budisten- 

 kalk) had been entire!}- removed, the weight of the remaining masses, 



