Volcanos and Earthquakes. 381 



great heights to the interior of the rocks, flows through warm- 

 er strata of earth, and then makes its exit in the valleys. It 

 is clear that such springs merely flow from above downwards, 

 when the raised strata make their appearance externally, but 

 that they will, on the other hand, rise again, if the strata are 

 upraised in the form of a trough on the opposite side. 



Phenomena lately observed, may perhaps present cases, where 

 the effect of the internal heat of the earth nearly approaches 

 the surface. Marcel de Serres,* for instance, describes a cave 

 near Montpelliej', situated in the Jura limestone, in which, at 

 depths of 135 and 150 feet, a constant temperature of 72o.5 F. 

 prevails, which exceeds by 10° the mean temperature of Mont- 

 pettier (6^°. 5). He shews that no accidental circumstance, 

 such as decompositions, the burning of tapers, or the respira- 

 tion of those who visit this cave, can be the cause of this phe- 

 nomenon ; but believes it is to be sought for in the central heat, 

 which rises through clefts and affects one point more, another 

 adjacent one less. Thus, at the distance of about 1200 feet 

 from this cave is found a cleft in the same formation, from 

 which issue watery vapours, whose temperature, 7S°.5 (that of 

 the external air being 52°-54j^.5), is nearly the same as of an 

 artesian well close in the vicinity of the cave (70°-72°). These 

 vapours, which probably rise from thermal springs existing 

 beneath, are constantly disengaged, and maintain a tempera- 

 ture of 73°.5, though in constant contact with the external air. 

 The cleft from which they issue, communicates with other 

 wider clefts, which expand into caves, into which the inhabi- 

 tants of the estate of Astier have already penetrated. The la- 

 bourers on this estate are in the habit of warming themselves 

 pretty frequently in the hole where these vapours are formed. 

 On examination, this vapour has all the purity of distilled 

 water. At an earlier period there existed, at the distance of 

 ]50 to 180 feet N.E. of the grotto of Astier, another opening 

 from which an equally warm vapour was evolved, which could 

 be perceived at some distance off*. This opening has, however. 



* Des Cavernes chaudes des environs de Montpellier in Annal. de Chim. 

 et de Phys. t. Ixv. p. 280. 



