266 EXPERIMENTS ON METAMORPHISM AND 



of dolomite, of gypsum, of a quartzose rock or quartzite, in fine chloritic 

 and talcose schists, which it would often be impossible to distinguish 

 from rocks of the same character, belonging to a well-characterized 

 Silurian formation. I will also call to mind, as Bischof has observed, 

 that the elementary composition of certain argillaceous schists of the 

 traui^ition formations is often very perceptibly the same as that of 

 granite and of gneiss. 



2. The same country will present instances of the passage, unques- 

 tionably gradual, of crystalline into stratified fossiliferous rocks. 

 These insensible transitions, which prevent the establishment of a 

 line of demarcation between these two categories of rocks, and that 

 suggested to Werner the name oi formation of transition, (Uebergangs- 

 gebirge,) which he gave to the group in which they occur most fre- 

 quently, have been too often described to make it necessary to enlarge 

 on this subject*. There are localities, however, especially in the 

 Alps, where crystalline rocks are inserted in the midst of sedimen- 

 tary rocks, which are but slightly modified. 



3. We know that the crystallization which has taken place in prox- 

 imity to eruptive rocks has not always effaced the trace of fossils. 

 Distinct vestiges of them still exist in the midst of rocks studded 

 with crystalline silicates. It is sufficient to cite the fossiliferous Silu- 

 rian limestone of Norway, which at Brevig contains paran thine and 

 garnet, and at Gjellebeck amphib'ole with epidote, the Jurassic lime- 

 stone of Angoumert, in the Ariege, containing dipyre; the schists of 

 Britanny, so well described by M. Boblaye, of which the same speci- 

 mens contain macles of several sixteenths of an inch in length, with 

 orthis, spiriferes, and calymenes; the white sub-crystalline limestone 

 containing encrinites, discovered in the Ural, on the borders of the 

 river Miask, by Murchison and de Verneuil, in the midst of a region 

 of granite, serpentine, and metamorphic rocks ;t in fine, the amphi- 

 bolic rock of Rothau, in the Vosges, in which polyps, without 

 changing their form, have been replaced by crystals of amphibole, 

 garnet, and axinite.:]: The same thing occurs in the masses of crys- 

 talline formations which we are now considering. Since the in- 

 stance cited by Brochant: De Charpentier, Lardy, and Studer, have 

 discovered in the neighborhood of St. Gothard belemnites in the 

 midst of a micaceous schist containing garnet. § The possibility 

 of a transformation appears, however, proved by the blocks 



-" Among the numerous examples that we could cite, it will be suflQcient to mention 

 Britanny, (Explication de la Carte Geologique de France, vol. i, p. 234 ;) Saxony, where these 

 transitions have been remarkably well described by Naumann ; the Alps of Dauphiny, of 

 the Tarentaise, of Switzerland, of Tyrol, of Saltzbourg, of Carinthia. according to Brochant, 

 Elie de Beaumont, Sismonda, Gras, Lory, Studer, Escher, Lardy, Favre, Murchisson, Cred- 

 ner, and many others ; the Ural, according to Murchisson and G. Eose, and the United 

 States, according to Lyell. 



The green schists in the different parts of the Alps (Grisons, Piedmont, &c.) form the 

 passage between rocks evidently sedimentary and those that are crystalline. — (Studer, Pkys- 

 ikalische Geographie, vol. i, p. 148.) 



t Rusiia in Europe and tlie Ural Mountains, vol i, p. 420. 



XAnnales des Mines, 5th series, vol. xii, p. 318. 



§ Particularly at the Col de la Nufenen, near Airolo. M. de Charpentier, as long ago 

 as 1822, found belemnites in the supposed primitive limestones of the Col de Seigne. — 

 (Cosmos, vol. i, p. 541.) 



