and tJieir Connexion with Volcanos. 55 



time the hot springs became suddenly cold. It has been re- 

 marked, that the earthquake which was experienced on the 25th 

 of May 1750, had for its central point the neighbourhood of the 

 Pyrenees ; for nowhere were its shocks so violent, or the damage 

 occasioned by it so considerable, as in that chain, especially in 

 the valley of Lavedar. The village, in which occurs the ther- 

 mal spring called Eaux cliaudes^ seems particularly exposed to 

 this visitation. In the case of the most recent of these earth- 

 quakes, that of the 22d of May 1814, it has been remarked that 

 the direction of the shock was nearly parallel to that of the chain 

 itself. 



The constitution of the thermal waters of the Pyrenees is such 

 as to confirm the idea of their being connected with volcanic ope- 

 rations. It will be seen by reference to my Description of Vol- 

 canos, page 376, that the gases resulting from the operations 

 which occasion them, are muriatic acid> sulphurous acid, sul- 

 phuretted hydrogen, carbonic acid, and nitrogen ; but that of 

 these, muriatic acid and sulphurous acid are chiefly emitted 

 during a period of vigorous action, whilst sulphuretted hydrogen, 

 carbonic acid, and nitrogen, generally make their appearance 

 when the process is in a more dormant condition. Now it is 

 important to observe, that, according to Longchamp, a chemist 

 expressly appointed by the late government of France to exa- 

 mine the mineral waters of that kingdom, azotic gas is disen- 

 gaged, often very abundantly, from every thermal water found in 

 or near the Pyrenees, and that sulphuretted hydrogen, though of 

 rare occurrence at the foot of these mountains, is almost univer- 

 sally present in the hot springs that make their appearance near 

 the axis of the chain. 



The local position, therefore, no less than the gaseous con- 

 tents, of most thermal waters in the Pyrenees, tend to confirm 

 the opinion, which their occurring at the foot, and in the bosom, 

 of an uplifted chain of mountains would of itself lead us to en- 

 tertain ; for although the cause of the elevation of extensive 

 tracts of country partakes of the uncertainty, belonging more or 

 less to all those effects, which have never been witnessed during 

 the period of their accomplishment, yet when we perceive that 

 the most analogous phenomena of which we have any experience 

 are attributable to earthquakes — themselves volcanic phenomena. 



