'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 eadier 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 Dufrenoy have pomted out, being found ow one side, and one 

 on the other. The springs issue immediately from trachyte, 

 which is most remarkably 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 1°.5) above 

 the mean of the soil. The strata of these rocks are raised, and 

 thereby produce a descent of the meteoric water lo 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 

 coincide 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 deep)ly 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 



* Forbes, loco cit, p. 607, 



