﻿1850.] MURCHISON ON THE MINERAL SPRINGS OF VICHY. 83 



Celestins the crack does not open downwards to a depth sufficient to 

 produce a change of temperature, or if ever such deep opening ex- 

 isted, it was probahly filled up along a fault. Beneath the waters 

 of the Hopital, on the contrary, there must still be an aperture ade- 

 quate to allow a considerable escape of heat ; whilst beneath the New 

 Establishment, or farther S.S.W., there is a still deeper and open 

 rent, by which additional gas escapes, and heats the water that has ac- 

 cess to it, up to the maximum temperature of nearly 45° Centigrade. 



A thermal spring exhibits a constancy from age to age which 

 never has been satisfactorily accounted for, except by supposing that 

 its heat is derived from a great internal and unchanging cause. How- 

 ever we may speculate on this point, the chemist must not forget, 

 that the geologist offers to him the elements to guide his first steps 

 in the inquiry. We show in this case, as in numberless other 

 examples, that the hot water issues from a line of fissure. At 

 Vichy, indeed, we may go farther, and try to explain when the fis- 

 sure was produced. My impression is, that toward the close of the 

 lacustrine tertiary period (and therefore at a very remote time as re- 

 spects the present surface) the arragonites and tuffs of the Celestins 

 were formed by very powerful and copious hot springs, and depo- 

 sited in more or less horizontal positions. For, although there are 

 no organic remains to prove that such was their age, all the physical 

 evidences point to that conclusion. I do not doubt that the hard 

 arragonite rocks of the Celestins formed the upper part of the lacus- 

 trine old tertiary series of the Limagne, which must have undergone 

 great upheavals en masse anterior to the establishment of the present 

 outlines of the land. The best proof of change of position in these 

 limestones is the fact stated in one of the opening paragraphs of this 

 memoir, viz. that there are no barriers whatever on the north by 

 which we can now account for the accumulation of such vast and 

 insulated deposits of terrestrial origin ; and that, therefore, the most 

 remarkable changes in physical outline have since been impressed 

 upon the whole region. 



The old lacustrine deposits, when formerly insulated by such bar- 

 riers from the sea, must, indeed, have occupied a considerable de- 

 pression, which underwent a succession of upheavals, accompanied 

 by the evolution at intervals of much igneous and volcanic rock. In 

 elevations of this extensive and massive nature there must necessarily 

 have been also open cracks, the result of sharp fractures, by which 

 the heat and gas escaped, and one of these was, I presume, the fis- 

 sure of Vichy, along which some communication with internal heat 

 has ever since been kept up. Now, in Central France (t. e. in Au- 

 vergne and the Vivarais, or the southern part of this very region) ig- 

 neous operations have been at work from periods of high antiquity, 

 until the crust assumed nearly all its present outlines, and when vol- 

 canos broke forth which poured their lava streams into the existing 

 valleys, as beautifully delineated in the work of Scrope*. I infer 

 that the dislocation at Vichy could not have taken place at this latter 



* Volcanos of Central France. 



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