SWISS VALLEYS. 243 



certained that the hot springs of Baden and Schinznach are 

 situated upon the line of such a rocky fissure ; and this is also 

 the case with the baths of Aix in Savoy *. 



With the stratified structure of the Swiss mountains the for- 

 mation of the valleys stands in the closest connexion. The un- 

 dulations of the mountains produced by upheaval are termed 

 longitudinal valleys; they are described as basin-valleys (fig. 

 361, B) when they spread between the saddle-mountains, as 

 fissure-valleys (fig. 361, D) when they are formed by the bursting 

 of the arch, and as combes (fig. 362, II, IV) when they lie be- 

 tween ridges running in the same direction. They also have 

 the form of clefts passing transversely through the mountain- 

 chains. 



When the outlet of a valley is closed by a transverse bar 

 formed either by a rock in position or by masses of debris, water 

 collects in it and a lake is produced. These accumulations of 

 water may be formed in basin-valleys, combes, and clefts; and. 

 to this is owing the varied character of the Swiss lakes f. Thus 

 the Lac de Joux is a basin-valley lake, whilst the lakes of Wal- 

 lenstadt and Brienz are regarded by Prof. Desor as combe-lakes, 

 and those of Thun and Lowerz as cleft-lakes. Others are of a 

 mixed nature : thus the arm of the Lake of the Four Cantons 

 which runs towards Fluelen, is a cleft-lake, and that extending 

 towards Unterwalden a combe-lake ; and the Italian lakes pre- 

 sent similar peculiarities. As in the cleft-lakes the rocky walls 

 ascend steeply, often nearly perpendicularly from the water, and 

 in many cases approach each other very closely (as on the Lac 

 de BrenSts), they have a remarkably picturesque character ; the 

 combe-lakes are sometimes surrounded by boldly rising rocky 

 masses ; and on the basin-lakes the slopes rise in gentle undu- 

 lations. 



As these lakes belong to a period of upheaval, and owe their 

 origin to fissures determined by the stratification of the moun- 



* Mousson, " Ueber die natiirlichen Verhaltnisse der Thermen von Aix " 

 (Denkschriften, 1847), and ' Geologische Skizze der Umgebungen von Ba- 

 den,' 1840. 



t This is demonstrated by Prof. Desor in his memoir u De la Physiognomie 

 des Lacs Suisses" (Revue Suisse, 1860), and "Quelques Considerations sur 

 la Classification des Lacs" (Atti Soc. di Lugano, 1861). 



R2 



