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GEOLOGICAL MEMOIRS. 



which particularly characterize the Central Alps. We must, however, 

 distinguish the indentations of the ridges thus effected from the great 

 independent peaks that often rise more than 1000 feet [French] 

 ahove the surrounding parts. The latter are, in all probability, con- 

 nected with the original formation of the mountain, and not result- 

 ing from the disintegrating of the atmosphere ; for, if weathering 

 and the rain have had the power to remove extensive beds of hard 

 rock from around an isolated peak, the latter itself ought also to have 

 entirely disappeared long since, as it offers for these operations a 

 proportionally far greater surface than a ridge. iVlthough the lime- 

 stone mountains are in general less peaked, in comparison, yet, on 

 account of their destructibility, and by the removal of the softer mate- 

 rials, gypsum and clay, they sometimes assume very curious forms. 

 Their pinnacles (needles, teeth), owing to the continual disintegra- 

 tion, fall in great masses, and cause the devastation so much dreaded 

 in their vicinity * . 



In treating of the Causes of the present forms of the Valleys and 

 Mountain-chains, it is stated, that both erosion by means of rivers 

 and the disintegrating effects of the atmosphere and its precipitations, 

 can be considered as having only subordinate influence on the forma- 

 tion of the Alpine districts. How (it is asked) is it possible for ero- 

 sion to have effected such equal declivities, not only of the valleys, 

 but also of the mountain ranges, and such a frequent regularity in 

 the distribution of elevations? How could it be possible for an 

 Alpine vallev to be excavated bv such means from the summit of 

 Mont Blanc down to a depth of 3000 feet [French] ? 



With regard to the sudden expansion of the basins, characterizing 

 the transverse valleys of the x\lps, it is stated (p. 200), that this could 

 not have been the result of violent outbursts of water ; it not being 

 possible for water to have collected in great masses where no dam 

 was present to restrain it ; and, if a dam had once existed, it could 

 only have been cut through by a deep gap, and not removed en- 

 tirely, without a trace being left through its whole extent. And at 

 p. 207, in considering how far great local collections of water may 

 have been concerned in the formation of these valleys, the author 

 observes, that were their figure due to this form of aqueous agency, 

 they must be regarded as cauldron-shaped cavities, that gradually 

 became filled with de'bris, and now offer levelled surfaces. But this 

 view is decidedly opposed not only by the fact of the very frequent 

 protrusion of the underlying rock, but by the usual occurrence of the 

 rock-surface at the slight depth of 10-12 feet [French] beneath the 

 superficial gravel. That the basin- or trough-like forms especially, 

 that is, the retreating of the sides of the valley on both sides, cannot 

 have been effected by the presence of a lake, is sufficiently clear. 

 We should otherwise confound the effect with the cause. The ques- 

 tion, whether collections of water have generally occupied these ca- 

 vities, is easily answered in most cases. We usually find here smaller 

 gravel-beds, that by their equal distribution are decidedly shown to 



* A notable example occurs in the case of the Diablerets near Bex. 



