S66 Prof. Bischof on the Natural History of 



thermal springs nearer the principal granitic mass are warmer, 

 while those more remote are colder. 



Professor Forbes has likewise pointed out, in an interesting 

 memoir on the temperatures and geological relations of certain 

 hot springs, particularly those of the Pyrenees^^ that, in the 

 departments of the Arriege and the Pyrenees Orientales, where 

 granite formations preponderate, in almost every case which 

 he has examined, if springs rise in granite, it is Just at 

 the boundary of that formation with a stratified rock. In a 

 great many cases it happens, that part of the springs rise from 

 granite^, and part from the slate or limestone in contact with it ; 

 and, he correctly observes, a more striking instance of the im- 

 mediate connexion between thermal waters and disturbed strata 

 could not be desired. t 



According to the observations of several geologists, the ter- 

 tiary rocks in the Pyrenees extend horizontally to the foot of 

 this chain, without entering, as the chalk, into the composition 

 of any part of its mass. Elie de Beaumont thence infers that 

 the Pyrenees received their position, relatively to the neigh- 

 bouring parts of the earth's surface, between the period of the 

 deposition of green sand and that of chalk (a formation, whose 

 raised strata, according to Dufrenoy's observations, ascend to the 

 crest of this chain), and before the deposition of the tertiary 

 strata of various ages.J We can very well explain, according 

 to this supposition, why the springs in the Pyrenees issue be- 

 tween the elevated granite and the raised strata of slate and 

 limestone. The circumstance above quoted from Pallasou, viz. 

 that the temperature of springs becomes lower, in proportion to 

 their distance from the principal granite-mass, may perhaps be 

 of little importance, since, according to the remark of Forbes, 

 cold sulphureous springs are to be found, even within not many 

 yards of others, having a high temperature, and almost an 

 identical mineral composition. Of this he has met with two 



* Philos. Transact, for 1836, p. 575. 



t At St Sauveiir and Thiiez, we have the co-ordinate, and, as Forhes 

 p. G02, rightly thinks, connected phenomena of intrusive rocks, dislocations 

 or fissures, metalliferous impregnation, and hot springs. 



t See Poggendorff's Annalen, t. xxv. p. 26, also p. 58. 



