62 



SIXTH REPORT — 183fi. 



Geological 

 position of 

 thermal 



springs : 



1st, near 

 volcanos. 



This, however, is controverted by Bischof *, who shows clearly 

 that no considerable augmentation could have arisen from sucii 

 a cause. 



Brongniart, in an article t in the Dlctionnaire des Sciences 

 Naturelles, has pointed out, that the temperature of thermal 

 springs is regulated by the nature of the rocks from which they 

 issue. 



The hottest are those associated with recent volcanos, next 

 those proceeding from extinct ones, or from primary rocks, and 

 lowest in the scale such as are connected with younger forma- 

 tions ; and though this ride may admit of exceptions, yet it 

 seems to hold good in the majority of cases. 



Now this observation of Brongniart will be found to har- 

 monize, and to point the same way, with the conclusions to 

 which I have myself been conducted by the study of thermal 

 springs, a summary of which will be found in an article in the 

 London Review fSr 1829, and in a memoir inserted in the Edin- 

 burgh New Philosophical Journal for 1831. 



In these publications I have attempted to show, that by far the 

 majority of thermal waters arise, either from rocks of a volcanic 

 nature, from the vicinity of some uplifted chain of mountains, 

 or lastly, from clefts and fissures caused by disruption. 



In many cases, indeed, all the above circumstances are seen 

 combined ; for the same spring may at once issue from the midst 

 of volcanic products, be situated at the foot of an uplifted chain, 

 and proceed out of a chasm or fissure ; so that, in classifying 

 springs according to the above plan, we should find many 

 perhaps possessing an equal claim to a place in all the three di- 

 visions. 



This circumstance, however, although it might prevent our 

 adopting the above distinction, as the basis of a classification of 

 mineral springs, only adds strength to the argument in favour of 

 a common origin being ascribed to them. 



With respect to the first of these classes of springs, I have 

 pointed out in a subsequent paper |, that they may be placed 

 under two heads, namely, first, those impregnated with gases 

 which are derived from volcanic energy, aiul probably owe their 

 origin to processes now continuing ; and secondly, those which, 

 from the absence of such accompaniments, seem to be nothing 

 more than reservoirs of water heated by coming into contact, 

 with a mass of rock, retaining some of the warmth it had acquired 

 from the volcanic operations of an antecedent period. 



The springs of Mount Dor, of Hungary, and some of those in 



* On Hot and Thermal Springs, Ed. Journal, 1836. f Eaux. 



i On a Spring at Torre del Annunziata in Edinb. New Phil, Journal, 1835. 



