Volcanos and Earthquakes. S7i 



thermal springs, although their temperature is for the most 

 part but little (often only 1°.5) above the mean of the soiL 

 The strata of these rocks are raised, and thereby produce a 

 descent of the meteoric water to deeper points ; nevertheless, 

 springs of this kind are very rare, wheje no volcanic masses 

 have been broken through. In these rocks slate-surfaces 

 (Schieferungs Flachen) are often found, which do not coincide 

 with the direction of the strata, but intersect them at an acute 

 angle. These slate- surfaces give origin here and there to mi- 

 neral springs, and a copious disengagement of carbonic acid 

 gas. 



By far the greater number of the mineral springs there rise 

 in valleys more or less deeply hollowed, on both sides of whose 

 declivities, conical volcanic rocks, chiefly of a basaltic nature, 

 have broken through. Some of them rise immediately from 

 the clay-slate rocks, frequently from the cleavage surfaces 

 which separate the strata of clay-slate and grey wacke, and some 

 come from volcanic masses (trass and volcanic ashes) which 

 cover these rocks. The circumstance that these mineral 

 springs seldom, perhaps never, flow out at the boundary between 

 the erupted masses and the fundamental rocks, gives us an in- 

 dication where to seek their origin. Tf the strata of the funda- 

 mental rocks A, A, Fig. 2, are inchned from the erupted volca- 



Fig.2. 



nic mass B, then a cleft will be formed to a great depth in the 

 interior of the earth at the boundary between this cone and the 

 fundamental rocks, in consequence of the contraction of the 

 former during its cooling. Down this cleft the meteoric water 

 penetrates and meets the streams of carbonic acid gas developed 

 in the interior. This latter is absorbed by the water, owing to 

 the strong hydrostatic pressure exerted at so great a depth. 

 This forms a water impregnated with carbonic acid, which 



