330 ON THE IGNEOUS METAMORPHOSIS [Ch. XIV. 



hornstone or compact felspar, effervesces slowly, and contains 

 a large portion of silica : how can this change be ascribed 

 to caloric ? It cannot be admitted that the limestone has 

 been fused and combined with the adjacent granite, because 

 it is stated that the lines of stratification are still preserved, 

 though the strata are much dislocated and disturbed : and 

 the chemist will not grant the possibility of carbonate of lime 

 being converted by heat into silica. Again, the quartz-rock 

 is in many positions nearly pure quartz even adjacent to the 

 granite, whilst at a considerable distance therefrom, where 

 the schistose beds are straight and undisturbed, this rock not 

 only contains felspar, but is so disposed in conjunction with 

 mica or hornblende as to form gneiss and even a perfect 

 granite, and when this is the case the adjacent slate is inter- 

 mediate between gneiss and mica-slate. How could granite 

 have produced this change on a remote mass of quartz-rock, 

 when that in its vicinity remains unaltered ? How could the 

 presence of granite cause the introduction of magnesia, alkali, 

 and other elements, into distant strata, through rocks which 

 are similar, and which may therefore be presumed to have an 

 equal affinity for such elements. 



Let us now turn to the crystalline limestones of the 

 Pyrenees, described by Dufrenoy. He has concluded that 

 the elevation of their strata, and their apparent gradation into 

 the succeeding fossiliferous rocks, prove that they belong to 

 the same mass, and that they have been altered and elevatgd 

 by the adjacent granite. The changes here indicated are, a 

 more crystalline texture, the presence of magnesia in the beds 

 next the granite, and the abundance of iron-ores : the con- 

 dition of its texture is only a character which this limestone 

 enjoys in common with most primary rocks. The nature of 

 the proof afforded by magnesia has been already considered ; 

 and the presence of metallic ores near the junction of granite 

 is certainly in itself no evidence of the manner in which the 

 containing rocks were formed. The questions of elevation 

 and transition have been already discussed : as regards the 



