and their Connexion with Volcanos. 53 



Nevertheless the occurrence of hot springs is rendered more 

 probable where both these conditions concur ; and hence we 

 shall generally find, that in mountainous tracts they are placed 

 in gorges which lie at a comparatively low elevation. Thus M. 

 Delarive has observed in the Alps, that the hot baths of St Ger- 

 vois are situated exactly on the spot which, of all others, com- 

 bines most completely the conditions, of approaching in the near- 

 est degree to the centre of the chain, and being at the same time 

 least elevated above the level of the ocean. 



Another very probable position for a thermal spring is near 

 the line, at which the elevation of a chain of mountains appears 

 to have commenced. Thus the springs of Dax, in the Depart- 

 ment des Landes, of Oleron near Pau, of Capvern near Ba- 

 gneres, of Encausse near St Gaudens, &c. occur near the hne 

 at which the mountains of the Pyrenees begin to rise from the 

 plain, the boundary, as it were, between the rocks that have 

 been uplifted, and those that were subsequently deposited. 



It is remarkable, that the hot spring of Aix, in Province, 

 gushes out just about the point at which the line of elevation 

 belonging to the Pyrenees would be intersected by another line 

 that should represent the elevation of the Dauphiny Alps, — a 

 position in which the chances of volcanic agency manifesting it- 

 self are of course doubled. The contiguity, also, of the baths of 

 Aix to some remarkable dislocations of the strata has been al- 

 ready pointed out by Messrs Murchison and Lyell, in their 

 memoir on the fresh-water formations of that district *, so that 

 here the third condition laid down as favourable to the appear- 

 ance of thermal waters concurs with the second. 



The particular circumstances connected with the geological 

 position of many thermal waters in Rousillon seemed also, so far 

 as T could judge from the cursory attention I was able to bestow 

 upon them last autumn, calculated to confirm that opinion of 

 their volcanic origin, which their general position, near the base 

 of an elevated chain of mountains, suggested. In several cases, 

 as at Aleth, Rennes, and Campagne, a change of dip seemed to 

 occur just where the springs burst out, coupled, in the case of 

 Aleth, with the fact of the gorge, through which the river Aude 

 passes just before it reaches the locality of the spring, being 



* Edinburgh New Philosophical Journal, No. 21. 



