370 Prof. Bischof on the Natural History of 



that at Lavey in the bed of Rhone in 1831 ; and others again 

 have become filled up. 



Among those which occur in the continuation of the princi- 

 pal Alpine chain, I will mention only the two most celebrated, 

 Pfeffers and Gastein. They are distinguished by their very 

 small proportion of solid and volatile ingredients. In fact 

 they are scarcely any thing more than warm glacier-watei'.* It 

 seems to me that these thermal springs, and probably many 

 others also in the Alps, resemble exactly those in Ischia, 

 which Daubeny supposes to be purely the result of the infiltra- 

 tion of water to spots in the interior of the earth retaining a 

 high temperature, with this difference only, that these spots lie 

 somewhat deeper in the 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 vol- 

 canic action, remarkable phenomena also present themselves, 

 with regard to the existence of thermal springs ; as, for instance, 

 in Auvergne, 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 

 dislocation ; two of the centres of elevation, which Elie de 

 Beaumont and Dufrenoy have pointed out, being found on one 

 side, and one on the other. The springs issue immediately 

 from trachyte, which is most remarkably and beautifully co- 

 lumnar just at the baths. These columns have an extremely 

 slaty cleavage perpendicular to their axes.t Although the 

 clay-slate rocks in the district of the Laacher See are very mas- 

 sive, and so far unfavourable to the penetration of meteoric 

 water to great depths, yet the number of mineral springs here 

 is very considerable. They belong, in general, to the class of 



* Of the thermal water of Gastein^ 10,000 parts contain only 3.5 solid 

 matter ; the same quantity of water from the iiiffscAiwe, which flows.imme- 

 diately out under the glacier, contains only 1, and that from the Aar at 

 Bern only, 2.2. 



t Forbes, loco cit. p. 607. 



