304: ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 



The highest temperature yet observed in the latter was at 

 Muudorff, viz,, 34 ° Centigrade. The following is a list of re- 

 markable thermal springs whose temperatures exceed that just 

 mentioned. 



Spring. Temperature. 



Pfaffera . 37.2° Centigrade. 



Wildbad 37.5 ° " 



Barreges 40.0° " 



Aix-la-Chapelle 44° to57.5° " 



Bath 46.25 ° » 



Leuck 50.2° " 



Aii in Savoy 54.3 ° " 



Ems 56.25.° « 



Baden-Baden 67.5 ° " 



Wiesbaden 70.0 ? " 



Carlsbad 75.0 ° » 



Burtscheid 77.5° " 



Katherine Spring in Caucasia „ 88.7 ° " 



Trincheros in Venezuela 97.0°* H 



We have here a series of temperatures, from the warmest yet 

 observed in artesian wells to that of boiling water, and it would 

 seem not unreasonable to suppose that the differences in their 

 temperatures correspond to differences in the depths of their 

 sources. It is true that the neighborhood of volcanoes or of 

 igneous rocks may heighten the temperature of springs rising from 

 comparatively shallow depths, but it is also the case that many 

 very hot springs occur in districts far distant from volcanic 

 regions. Thus it is with the hot spring of Hammam-mes-Kutin, 

 betwixt Bone and Gonstantine, the temperature of which is 

 stated at from 60 ° to 95 ° Cent. ; and also with the warm 

 springs in Cape Colony, which, according to Kraus, break forth 

 from sandstone, far from any plutonic rock.f It is clearly impos- 

 sible to account for the differences in the temperatures 

 of thermal springs in any other way than by supposing 

 that the springs possess very nearly the temperatures of the 

 depths from which they rise, and that the higher the temperature 

 of the water the deeper is the source from which it springs. We 

 are therefore justified in regarding it as fully proved that the tem- 

 erature of the earth increases with the depth, until a point is 



* Muller's Kosmische Physik, p. 340. 

 f Naumann'g Geognosie, I, 206. 



