GEOLOGY. 213 



limestone in the summit and lower precipices. This limestone wave 

 was shown to be one of a great series, running parallel with the Alps, 

 and constituting an undulatory district, chiefly composed of chalk beds, 

 separated from the higher limestone district of the Jura and lias by a 

 long trench or moat, filled with members of the tertiary series chiefly 

 nummulite, limestones, and flysch. 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 tendency to lean toward 

 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 frac- 

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

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

 ed valleys exist. Thus, the Mont Vergi and the Aiguilles of Salouvre 

 are only fragmentary remains of a range of horizontal beds, once con- 

 tinuous, but broken by this transverse system of curvilinear cleavage, 

 and worn or weathered into separate summits. The means of this ulti- 

 mate sculpture or Aveathering were lastly to be considered. 



3. 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 tempera- 

 ture and atmosphere. All important existing forms are owing to dis- 

 integration, 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 energetic effects of it being merely the ex- 

 ponents of disintegration. A glacier did not produce its moraine, but 

 sustained and exposed the fragments which fell on its surface, pulver- 

 izing these by keeping them in motion, but producing very unimport- 

 ant 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 carrying 

 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 carriage is unlimited, and 

 when masses of earth or rock are once loosened, the glacier carries 

 them away, and exposes fresh surfaces. Generally, the work of water 

 and ice is, in mountain surgery, like that of lancet and sponge, one 

 for incision, the other for ablution." No excavation by ice was possi- 

 ble on a large scale, any more than by a stream of honey ; and its va- 

 rious 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 Prof. James Forbes. The existing forms of 

 the Alps are, therefore, traceable chiefly to denudation as they rose 

 from the sea, followed by more or less violent aqueous action, partly 

 arrested during the glacial periods, while the produced diluvium was 

 carried away into the valley of the Rhine or. into the North Sea. One 

 very important result of denudation had not yet been sufficiently re- 



