ON THE FORMATION OF CRYSTALLINE ROCKS. 299 



garnet and magnetic iron, present, notwithstanding, a very regular 

 alignment. 3d. I have observed, in experiments similar to those of 

 Sorby, that the spangles really have a tendency to arrange them- 

 selves gradually in the direction of the movement determined by the 

 pressure, in such a way that the friction resulting from the .sliding 

 will be the least possible. Nevertheless, their alignment is very 

 imperfect in comparison with that of nature, often so remarkable in 

 its regularity, and that of these spangles, those which are not able to 

 arrange themselves in the general plane, appear to disturb the for- 

 mation of the lamellie. 4th. A process has given me results which 

 are almost identical with those of nature; it consists in impregnating 

 clay, before submitting it to lamination, with water heated to 100^ 

 centigrade, and saturated with boracic acid; then laminating it on a 

 plate of cast iron heated by a furnace, so as to avoid the precipitation 

 of the acid before the formation of lamellas. But in this experiment 

 the spangles of boracic acid, which are produced between the lamellas 

 by an ulterior cooling of the liquid, present an alignment infinitely 

 more regular than in the experiment of Sorby, and altogether 

 like that of certain micaceous schists.* 



By comparing the fticts which we have just cited with the data 

 which the metamorphism at Plombieres has furnished us, we arrive at 

 a conclusion of the highest probability. If the materials, concrete 

 or bricks, into which the water of Plombieres penetrates had a lamel- 

 lar structure, is it not evident that the mode of circulation of the 

 water would have been influenced, and that the liquid veins insinu- 

 ating themselves in preference between the laj^ers would have given 

 rise on their passage to crystals in lamellae or otherwise sensibly 

 aligned ? In the case where the metamorphism would not have taken 

 place but by a water of constitution, we yet comprehend that the 

 crystals would be developed profiting by the planes of cleavage in 

 the mass. The papyraceous arrangement, so remarkable in its regu- 

 larity, which the quartz of some leptynites and porphyries presents, 

 may have had an analogous origin, since, as we have seen, water inter- 

 venes also in the crystallization of eruptive rocks. 



CHAPTER XII. 



COMPAEISON OF ALL THE PHENOMENA WHOSE SEAT IS IN THE INTERIOR OP 



THE EARTH. 



If thermal springs are the agents of metamorphism, we need not 

 be surprised that the same mode of metamorphism extends over ex- 

 tended regions, since we still see mineral waters grouped together 

 in families of analogous composition in regions of great extent; thus 

 they are generally carbonated in Auvergue and Eifel, sulphurous in 



* I do not, however, pretend to say that this lamination in some cases has not continued 

 after the alignment of the spangles in the rocks ; it is easy to be convinced of the contrary 

 by examining the different schistose crystalline rocks. 



