ON ITS EXTERIOR. THERMAL SPRINGS. 205 



and formative. In this point of view they are of great 

 geological importance. Senarmont has shown with ad- 

 mirable sagacity the manner in which it is highly proba- 

 ble that many veins, ancient channels of thermal waters, 

 have been rilled from below upwards by deposits of the 

 elements which had been held in solution. By changes 

 of pressure and temperature, by internal electro-che- 

 mical processes, and by the specific attraction of the 

 side walls, lamellar divisions have taken place and con- 

 cretions have been formed. Drusic cavities and porous 

 amygdaloids seem to have been formed partly in this 

 manner. When the deposit in veins has taken place in 

 parallel zones, these zones correspond to each other as 

 respects their constitution, for the most part symme- 

 trically from the sides. 



Senarmont's chemical ingenuity succeeded in obtaining 

 artificially a considerable number of minerals by quite 

 analogous, synthetic processes. ( 283 ) I hope that a scienti- 

 fically gifted observer, nearly connected with myself, 

 will shortly publish a new and important investigation 

 respecting the temperatures of springs, in which, by in- 

 duction from a long series of observations, he will treat 

 the intricate phenomena of disturbing effects with great 

 generality. Eduard Hallmann, in the thermoinetric 

 measurements obtained by him during the years from 

 1845 to 1853 in Germany (on the Rhine), and in Italy (in 

 the country round Rome, in the Alban hills, and in 

 the Apennines), distinguished between, 1st, pure meteor- 

 ological springs, whose mean temperature is not raised 

 by the internal temperature of the earth ; 2nd, mete- 

 orolo-geological springs; which being independent of 

 the distribution of rain, and warmer than the atmo- 



