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Ch. XVIL] 



MINEEAL AND TIIEEMAL SEEINGS 



9 95 



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that in many cases we can best account for the rise of large 

 bodies of water from great depths ; nor can we hesitate to 

 admit the adequacy of the cause, if we suppose the expansion 

 of the same elastic fluids to be sufficient to raise columns of 

 lava to the lofty summits of volcanic mountains. Several 

 ouses, the carbonic acid in particular, are disengaged in a free 

 state from the soil of various districts, especially in regions of 

 active or extinct volcanos ; and the same are found more or 

 less intimately combined with the waters of all mineral 



both cold and thermal. Dr. Daubeny and other 

 writers have remarked, not only that these springs are most 

 abundant in volcanic regions, but that when remote from 

 them, their site usually coincides with the position of some 

 great derangement in the strata ; a fault, for example, or 

 great fissure, indicating that a channel of communication has 

 been opened with the interior of the earth at some former 

 period of local convulsion. It is also ascertained that at 

 great heights in the Pyrenees and Himalaya Mountains, hot 

 springs burst out from granitic rocks, and they are abundant 

 in the Alps also, these chains having all been disturbed and 

 dislocated at times comparatively modern, as can be shown 

 by independent geological evidence. 



The small area of volcanic regions may appear, at first 

 sight, to present an objection to these views, but not so when 

 we include earthquakes among the effects of igneous agency. 

 A large proportion of the land hitherto explored by geologists, 

 can be shown to have been rent or shaken by subterranean 

 movements since the oldest Tertiary strata were formed. It 

 will also be seen, in the sequel, that new springs have burst 

 out, and others have had the volume of their waters aug- 

 mented, and their temperature suddenly raised after earth- 

 quakes, so that the description of these springs might almost 

 with equal propriety have been given under the head of 

 ' igneous causes/ as they are agents of a mixed nature, being 

 at once igneous and aqueous. 



As examples of changes which have occurred in historical 

 times, I may here mention, that during the great earthquake 

 at Lisbon in 1755, the temperature of the spring called La 

 Source de la Seine at Bagneres de Luchon, in the Pyrenees, 



