56 Prof. Bischof on the Natural History of 



the baths of Bertrich, are to be met with ; although in the two 

 latter districts, the number of thermal springs, whose tem- 

 perature exceeds that of the soil at the most by a few degrees, 

 are enormous, and considerable exhalations of carbonic gas 

 give evidence of former volcanic action. It may, however, 

 be conjectured, with some probability, that in the vicinity of 

 the Laacher See and in the Eifel, springs may have existed, 

 whose duration depended on the cooling of the masses of lava. 

 Similar circunistances seem to have occurred in Auvergne and 

 Vivarais, although the hot-springs, which are not uncommon 

 in those countries, show that many of the former volcanic chan- 

 nels are still unobstructed. 



The examination of deposits obviously formed from springs* 

 which existed at a former time, may often present an indication 

 of their temperature. Thus, on the volcanic tongue of land 

 called the Sneefield-Syssel^ in Iceland, we find none of the hot 

 mineral springs which are so numerous in other parts of the 

 island, and which are distinguished by their holding silica in 

 solution, and exhaling sulphureted hydrogen gas. But, in 

 former times they existed here, for in many places we find sili- 

 ceous incrustations in the form of tuflfas and sinters. One cold 

 spring, which is now flowing, has certainly taken the place of 

 a hot siliceous spring, for its present deposits are only calca- 

 reous, and quite distinct from the older incrustations.* The 

 circumstance that arragonite is deposited from hot-springs, 

 calcareous spar, on the other hand, from cold ones, gives us 

 also an indication of this kind. Since G. Roset pointed out 

 that the former is only deposited from a hot solution of car- j 

 bonate of lime, the occurrence of arragonite in any deposit 

 leads us to infer with certainty that these deposits owe their ^ 

 origin to a hot spring. If, on the contrary, we find calcareous 

 spar in any deposit, we may infer with equal certainty that it 

 was produced by a cold spring. J 



* K. V. NiJda, loco cit. p. 282. f Poggendorff's Annal. t. xl. ^. 353. 



4: The following remark may not be" entirely superfluous, viz. accord- 

 ing to G. Hose, arragonite is formed in a higher temperature only in , 

 the moist way, hut calcareous spar is formed in the dry way. Thus car- 

 bonate of lime crystallizes from a state of fusion under strong pressure 

 only in the form of calcareous spar. Arragonite exposed to a slight red 

 Jieat is easily converted into calcareous spar. 





