56 Natural History of Volcanos and Earthquakes. 



A spring arising from beneath, leads us to conclude that me- 

 teoric water penetrates through clefts which communicate low 

 down with the former. The experience gained in boring arte- 

 san wells, shows that a succession of strata is most favorable for 

 such processes, and from causes easily explained. In what are 

 called primary rocks, however, no such alteration of strata is 

 found, because they are not stratified. The usual occurrence, 

 viz., the flowing of meteoric water down inclined surfaces of 

 stratification which appear at elevated situations, and the rising of 

 this water, by means of natural or artificial channels, after having 

 been forced down to a more or less considerable depth, cannot 

 then happen in unstratified rocks. It appears, nevertheless, that 

 there are granitic rocks traversed by clefts more or less perpen- 

 dicular, and communicating low down. Thus at Ahej^dee7i, in 

 Scotland, water has been drawn by boring in granite 180 feet be- 

 low the surface, which, according to Robison, came from a cleft 

 filled with sand and gravel, and rises six feet above the level of 

 the earth.* Such a conununication of the clefts low down, must, 

 however, occur but rarely. 



If the primary mountain rises above its environs and the 

 clefts at its base lie exposed, then will the springs .flow out of the 

 clefts. Such an origin of springs, which are not naturally ris- 

 ing springs, is often observed at the foot of basaltic and trachytic 

 cones, &c. 



On the other hand, on the limits between stratified and un- 

 stratified rocks, where the latter have traversed the former, and 

 where channels extending to a great depth have been formed in 

 consequence of the contraction of the traversed masses during 

 their cooling, circumstances favorable to these rising springs ex- 

 ist, and it is easy to conceive, therefore, that thermal springs may 

 be found on the limits of these interrupted masses, but not in their 

 interior. 



Let us imagine a stratified chain of mountains consisting of 

 several formations in a perfectly horizontal position, whose new- 

 est portion (jiingstes Glied) is much fissured, and under which 

 an impervious stratum lies, then the meteoric water will penetrate 

 the former fissured stratum, but be retained by the latter. As 

 long as this horizontal position remains undisturbed, no rising 



* Compt. Rend. 183 No. 24, p. 575, and t. ii, No. 20, p. 583. 



