‘Natural History of Volcanos and Earthquakes. 63 
Alps than at Ischia, where the hot masses approach nearer to the 
surface in consequence of volcanic activity. 
In regions where, after the earlier general elevations, later 
partial fractures and elevations have been produced by volcanic 
action, remarkable phenomena also present themselves, with re- 
gard to the existence of thermal springs; as for instance, in Au- 
vergne, and in the vicinity of the Laacher See. 
In regard to the former, it is worthy of remark, that the baths 
of Mont-Dore are situated almost at the geographical centre of 
that group of hills, and also at the position of greatest disloca- 
tion; two of the centres of elevation, which Elie de Beaumont 
and Dufrénoy have pointed out, being found on one side, and one 
on the other, The springs issue immediately from trachyte, 
which is most remarkabl y and beautifully columnar just at the 
baths. These column have an extremely slaty cleavage perpen- 
dicular to their axes.* Although the clay-slate rocks in the dis- 
trict of the Laacher See are very massive, and so far unfavorable 
to the penetration of meteoric water to great depths, yet the 
number of mineral springs here is very considerable. They be- 
long, in general, to the class of thermal springs, although their 
temperature is for the most part but little (often only 19.5) 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, where no vol- 
canic masses have been broken through. In these rocks slate- 
Surfaces (Schieferungs Flachen) are often found, which do not 
Colucide with the direction of the strata, but intersect them at 
an acute angle. These slate-surfaces give origin here and there 
to mineral springs, and.a copious disengagement of carbonic 
acid gas. 
By far the greater number of the mineral springs take their rise in 
Valleys more or less deeply hollowed, on both sides of whose de- 
Clivities, 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 greywacke, and some come from vol- 
Canic masses (trass and volcanic ashes) which cover these rocks. 
The circumstance that these mineral springs seldom, perhaps 
ee necag ie yf 
* Forbes, loco cit, p. 607. 
