’ Natural History of Volcanos and Earthquakes. 259 
latter districts, the number of thermal springs whose tempera- 
ture exceeds that of the soil at the most by a few degrees, are 
enormous, and considerable exhalations of carbonic gas give 
evidence of former galvanic action. It may, however, be con- 
jectured, 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. Sim- 
lar circumstances seem to have occurred in Auvergne and Vi- 
varais, although the hot springs, which are not uncommon in 
those countries, show that many of the former volcanic channels 
are still unobstructed. 
he 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 so- 
lution, and exhaling sulphureted hydrogen gas. But, in former 
limes they existed here, for in many places we find siliceous in- 
frustations in the form of tuffas 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 calcareous, and 
quite distinct from the older incrustations.* The circumstance 
that atragonite is deposited from hot springs, calcareous spar, 
% the other hand, from cold ones, gives us also an indication 
of this kind. Since G. Rose+ pointed out that the former Is 
only deposited from a hot solution of carbonate of lime, the 
®ecurrenice of arragonite in any deposit, leads us to infer with 
*ettainty, 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. t 
If the melted nucleus of the earth be the common seat of the 
Volcanic activity of the whole earth, subterranean communica- 
t Poggendorff’s Annal. t. xl, p. 353. 
viz. according to G, 
