I INACCESSIBLE VALLEYS 27 



causes which determined their direction of flow were of 

 an altogether different nature. And as regards what 

 used to be considered the most striking cases of " valleys 

 of disruption " — the narrow defiles and gorges like those 

 of the Trient and the Reuss — it may now be affirmed, 

 that in no single instance which has been carefully 

 examined has any evidence of an open fissure been dis- 

 covered, while in most cases there is the clearest proof 

 that the gorges in question have been wholly excavated 

 by the action of running water under conditions which 

 are explained in Chapter V. 



It was for the purpose of bringing clearly before non- 

 geologic readers the total inaccuracy of the popular view 

 — that every rock-walled valley or deep Alpine gorge has 

 had its origin in some great " convulsion of nature " — and 

 to impress upon such readers the grand but simple theory, 

 which we owe mainly to the late Sir Charles Lyell, of 

 the efficiency of causes now in action in producing the 

 varied contours of the earth's surface, that this account of 

 some of the most remarkable of known valleys has been 

 written. 



