SCO Prof. Tyndall on the Conformation of the Alps. 



of broad valleys. Such a fissure might enter into the list of acci- 

 dents which gave direction to the real erosive agents which scooped 

 the valley out ; but the formation of the valley, as it now exists, 

 could no more be ascribed to it than the motion of a railway train 

 could be ascribed to the finger of the engineer which turns on 

 the steam. 



These deep gorges occur, I believe, for the most part in lime- 

 stone strata; and the effects which the merest driblet of water 

 can produce on such rocks are quite astonishing. It is not un- 

 common to meet chasms of considerable depth produced by small 

 streams the beds of which are dry for a large portion of the year. 

 Right and left of the larger gorges such secondary chasms arc 

 usually to be found. The idea of time must, I think, be more 

 and more included in our reasonings on these phenomena. Hap- 

 pily the marks which the rivers have, in most cases, left behind 

 them, and which refer, geologically considered, to actions of 

 yesterday, give us ground and courage to conceive what may be 

 effected in geologic periods. Thus the modern portion of the Via 

 Mala throws light upon the whole. Near Bergiin in the Valley 

 of the Albuia there is also a little Via Mala which is not less 

 significant than the great one. The river Hows here through a 

 profound limestone gorge; but to the very edges of the gorge we 

 have the evidences of erosion. The most striking illustration of 

 water-action upon limestone rock which I have ever witnessed is, 

 I think, furnished by the gorge at Pfaffers. Here the traveller 

 passes along the side of the chasm midway between top and 

 bottom. Whichever way he looks, backwards or forwards, up- 

 wards or downwards, towards the sky or towards the river, he 

 meets everywhere the irresistible and impressive evidence that 

 this wonderful fissure has been sawn through the mountain by 

 the waters of the Tamina. 



I have thus far confined myself to the consideration of the 

 gorges formed by the cutting through of the rock barriers which 

 frequently cross the valleys of the Alps ; as far as I have ex- 

 amined them they are the work of erosion. But the larger ques- 

 tion still remains, To what action are we to ascribe the formation 

 of the valleys themselves ? This question includes that of the for- 

 mation of the mountain ridges ; for were the valleys wholly filled, 

 the ridges would disappear. Possibly no answer can be given to 

 this question which is not beset with more or less of difficulty. 

 Special localities might be found which would seem to contradict 

 every solution which refers the conformation of the Alps to the 

 operation of a single cause. Still the Alps present features of a 

 character sufficiently definite to bring the question of their origin 

 within the sphere of close reasoning. That they were in 

 whole or in part once beneath the sea will not be disputed. They 



