86 



rocks, granite, slate, or basic limestone, these are generally 

 sulphurous and salt, and moderately warm, and these, or many 

 of them, seem to have this curious characteristic, that they show 

 an inconstant temperature of their sources. Those at the Bagneres 

 de Luchon Avere cold springs until after an earthquake that took 

 place in the year 1755; those at Eigorre were by an earthquake 

 in the previous century, in 1660, temporarily rendered cool, 

 though they soon recovered their heat ; those hot springs such as 

 at Aix la Chapelle, and some of the German and other springs 

 that were known and used by the Eomans, would appear to have 

 become warmer since their times, for they apparently used them 

 for bathing direct from the source, without any cooling, which 

 could not now be done. 



The last class of springs which we will now examine, appear to 

 have a very equable temperature, though not so high as those 

 that rise from near the granite. 



The first general characteristic of this class is that they arise 

 from, or close above the Carboniferous limestone, the water appear- 

 ing to well up through some natural fissure or fault, which follows 

 the joint lines of the rock ; hence the water that has penetrated 

 from the surface following the planes of stratification, being the 

 lines of least resistance, again comes to the surface by natural 

 fissures acting like Artesian wells (presuming that the opening of 

 these fissures is below the level of the edges or out-crop of the 

 strata where the water enters), the water consequently may 

 traverse the lines of stratification for a long distance, taking the 

 short cut of the joint opening for its exit. 



The usual manner of accounting for hot springs appearing above 

 the surface of the earth has })een thus : — It has been supposed 

 that the water from the surface has descended into the lower 

 regions, where it has come into contact with heated rock, the 

 consequence of the internal heat of the globe, and that this has 

 generated steam and gases Avhich have then forced the water thus 

 heated to the surface. 



