Prof. Tyndall on the Conformation of the Alps. 263 



are compelled to resort to local disturbances, the manipulation 

 of the earth's crust which will be necessary to obtain the valleys 

 and the mountains will, I imagine, bring the difficulties of the 

 theory into very strong relief. Indeed an examination of the 

 region from many of the more accessible eminences — from 

 the Galenstock, the Grauhaupt, the Pitz Languard, the Monte 

 Confinale — or, better still, from Mont Blanc, Monte Rosa, 

 the Jungfrau, the Finsteraarhorn, the Weisshorn, or the Mat- 

 terhorn, where local peculiarities are toned down, and the ope- 

 rations of the powers which really made this region what it is 

 are alone brought into prominence, must, I imagine, convince 

 every physically minded man of the inability of any fracture 

 theory to account for the present conformation of the Alps. A 

 correct model of the mountains, with an unexaggerated vertical 

 scale, produces the same effect upon the mind as the prospect 

 from one of the highest peaks. We are apt to be influenced 

 by local phenomena which, though insignificant in view of the 

 general question of Alpine conformation, are, with reference to 

 our customary standards, vast and impressive. In a true model 

 those local peculiarities disappear ; for on the scale of a model they 

 are too small to be visible ; while the essential facts and forms 

 are presented to the undistracted attention. 



A minute analysis of the phenomena strengthens the conviction 

 which the general aspect of the Alps fixes in the mind. We 

 find, for example, numerous valleys which the most ardent plu- 

 tonist would not think of ascribing to any other agency than 

 erosion. That such is their genesis and history is as certain as 

 that erosion produced the Chines in the Isle of Wight. From 

 these indubitable cases of erosion — commencing, if necessary, 

 with* the small ravines which run down the flanks of the ridges, 

 with their little working navigators at their bottoms — we can 

 proceed, by almost insensible gradations, to the largest valleys 

 of the Alps ; and it would perplex the plutonist to fix upon the 

 point at which, in his opinion, fracture begins to play a mate- 

 rial part. In ascending one of the larger valleys, we enter it 

 where it is wide and where the eminences are gentle on either 

 side. The flanking mountains become higher and more abrupt 

 as we ascendj and at length we reach a place where the depth of 

 the valley is a maximum. Continuing our walk upwards we 

 find ourselves flanked by gentler slopes, and finally emerge from 

 the valley and reach the summit of an open col, or depression in 

 the chain of mountains. This is the common character of the 

 large valleys. Crossing the col, we descend along the opposite 

 slope of the chain, and through the same series of appearances in 

 the reverse order. If the valleys on both sides of the col were 

 produced by fissures, what prevents the fissure from prolonging 



