396 



MINERAL AND THERMAL SPRINGS. 



[Ch. XVII, 



a 



re- 



was suddenly raised as much, as 75° F., or changed from f 

 cold spring to one of 122° F., a heat which it has since 

 tained. It is also recorded that the hot springs at Bagneres 

 de Bigorre, in the same mountain-chain, became suddenly 

 cold during a great earthquake which, in 1660, threw down 

 several houses in that town. 



But how, it will be asked, can the regions of volcanic heat 

 send forth such inexhaustible supplies of water ? The diffi- 



m 



able, if we believed that all the atmospheric waters found 

 their way into the basin of the ocean ; but in boring near the 



meet 



most 



bottom 



much 



Yet, 



may 



sinks beneath the floor of the ocean, through the porous 



com 



in it by earthquakes. After penetrating to a considerable 

 depth, this water may encounter a heat of sufficient intensity 

 to convert it into vapour, even under the high pressure to 

 which it would then be subjected. This heat would probably 

 be nearest the surface in volcanic countries, and farthest from 

 it in those districts which have been longest free from erup- 

 tions or earthquakes. 



In corroboration of such an opinion, I may mention, that 

 in regions where volcanic eruptions still occur, hot springs are 

 abundant, and occasionally attain a boiling temperature, 

 while in proportion as we recede from such centres of igneons 

 activity, the thermal waters decrease in frequency and average 

 heat. In central France, or in the Eifel in Germany, where we 

 find cones and craters so perfect in their form, and streams of 

 lava bearing such a relation to the shape of existing valleys, 

 as to indicate that the internal fires have become dormant in 

 comparatively recent times, hot springs play a conspicuous part. 



It would follow from the views above explained, that there 

 must be a twofold circulation of terrestrial waters ; one caused 

 by solar heat, and the other by heat generated in the interior 



of our planet. We 



the land would be unfit for 



vegetation, if deprived of the waters raised into the atmo- 











CH' 



ss 



w 



o^ ] 



s 



the 

 many 



up 



fr 



f a: 



then 



As 



jfet : 



whicl 



may 



whicl 

 of sir 



alum 



muri: 

 acid, 



also : 



Tb 

 chloi 

 stitui 

 hast 

 often 

 desc( 

 com* 

 inti 

 hots 

 rock 



after 



tak 



of 



i 



e 



A: 



spii 

 gas 



i 



!( 









