ON THE FORMATION OF CRYSTALLINE ROCKS. 267 



which come from Mount Somma, where there is every description of 

 transition, from the compact Hmestone of the Apennines, containing 

 pectunculus, to the lamellar limestones and to dolomites, filled with 

 crystallized sihcates. 



4. In rocks in which the crystalline state is still more distinctly 

 marked, where no traces of animal forms are any longer to be seen, 

 the remains of plants are sometimes preserved. We find, for in- 

 stance, vegetable imprints in feldspathic and micaceous rocks, which 

 are so crystalline that they might be mistaken for eruptive rocks, 

 especially if they were to be determined by isolated specimens. 

 Such are the feldspathised grauwacks of Thann, the schists of Bus- 

 sang, in the Vosges, the pierre carree of the banks of the Loire, which 

 is frequently associated with anthracite, rocks which are assigned to 

 the carboniferous or anthracite formation. 



5. When the forms of the vegetables themselves are no longer 

 found, these schistose crystalline rocks often contain carbonaceous 

 compounds which, in all probability, are of organic origin. It is thus 

 that the micaceous schists of Ariolo, which are studded with garnets 

 and long prisms of amphibole, still contain, according to an assay 

 that I made of them, as much as 5 per cent, of carbon;* the same is 

 true of many slaty schistsf. 



It follows, from what precedes, that it would be difficult to estab- 

 lish a distinction between metamorphism of juxtaposition and regional 

 metamorphism, if we were to judge by mineralogical characters only; 

 the two phenomena differ principally in the extent of their action. 

 It is chiefly in the lower beds of the series of stratified formations 

 that the effects of regional metamorphism are remarkable. 



A splendid example of the transformation of the palaeozoic forma- 

 tions occurs in the Ural: the sedimentary origin, and the age of 

 the crystalline schists which compose it, have been placed beyond 

 question by the admirable work of Murchison, De Verneuil, and 

 Keyserling.l The very feebly consolidated silurian formations of 

 Russia, in these mountains are transformed into crystalline schists, 

 which have here and there preserved, as if to prove their origin, 

 strips of fossiliferous rocks. The same is true of the carboniferous 

 formation. The white and soft limestones of Moscow are found in 

 the Ural with the same fossils. {Productus gigas and Spirifer 7nosquen- 

 si'.s,) but under the form of a hard, dark, and crystalline limestone. 

 Regional metamorphism, however, is not exclusively confined to the 

 primitive formations, and, on the other hand, it does not, of necessity, 

 belong to them. Thus, on the one side, we find schists that have be- 

 come crystalline as high up as the beds containing belemnites, and 

 even in the nummulitic formation, (as in the Grisons.§) On the other 



- After having removed the carbonate of lime by an acid, the carbon was determined by 

 the oxide of copper, as in organic analyses. 



f It is very possible that the bituminous matter found by M. Delesse in the protogine of 

 Mount Blanc is of organic origin. 



f Russia, vol. i, pp. 402, 438, and 4G5. 



§ According to Sir R. Murchison, these rocks are allied to gneiss. — {Geological Quarterly 

 Journal, vol. v, p. 211, 1848.) 



