261 



made argillaceous schist granular, as was observed by Gustav 

 Rose and myself in the Altai mountains (within the fortress of 

 Buchtarminsk),* and have transformed it into a mass resem- 

 bling granite, consisting of a mixture of feldspar and mica, in 

 which larger laminae of the latter were again imbedded.! 

 Most geognosists adhere, with Leopold von Buch, to the well- 

 known hypothesis " that all the gneiss in the Silurian strata of 

 the Transition formation, bctM r een the Icy sea and the Gulf of 

 Finland, has been produced by the metamorphic action of 

 granite.} In the Alps, at St. Gothard, calcareous marl is 

 likewise changed from granite into mica-slate, and then trans- 

 formed into gneiss." Similar phenomena of the formation of 

 gneiss and mica-slate through granite present themselves in 

 the oolitic group of the Tarantaise, in which belemnites are 

 found in rocks, which have some claim to be considered as 



* Rose, Reise nacJi dem Ural, bd. i. s. 586-588. 

 t In respect to the volcanic origin of mica, it is important to notice 

 that crystals of mica are found in the basalt of the Bohemian Mittelgc- 

 birge, in the lava that in 1822 was ejected from Vesuvius (Monticelli, 

 Storia del Vesuvio neyli Anni 1821 e 1822, 99), and in fragments of 

 argillaceous slate imbedded in scoriaceous basalt, at Hohenfels, not far 

 from Gerolstein, in the Eifel, (see Mitscherlich, in Leonhard, Basalt- 

 Gebilde, s. 244). On the formation of feldspar in argillaceous schist, 

 through contact with porphyry, occurring between Urval and Poiiet 

 (Forez), see Dufrenoy, in G6ol. de la France, t. i. p. 137. It is probably 

 to a similar contact, that certain schists near Paimpol in Brittany, with 

 whose appearance I was much struck,, while making a geological pedes- 

 trian tour through that interesting country with Professor Kunth, owe 

 their amygdaloid and cellular character, t. i. p. 234. 



J Leopold von Buch, in the AWiandlungen der ATcad. der Wissen- 

 scliaft zu Berlin, aus dem J. 1842, s. 63, and in the Jahrbilchern fur 

 Wissensclwftliclie Kritik Jalirg. 1840, s. 196. 



Elie de Beaumont, in the Annales des Sciences Naturelles, t. xv. 

 p. 362-372. " In approaching the primitive masses of Mont Rosa, and 

 the mountains situated to the west of Coni, we perceive that the 

 secondary strata gradually lose the characters inherent in their mode of 

 deposition. Frequently assuming a character apparently arising from a 

 perfectly distinct cause, but not losing their stratification, they some- 

 what resemble in their physical structure a brand of half-consumed 

 wood, in which we can follow the traces of the ligneous fibres beyond 

 the spots which continue to present the natural characters of wood." 

 vSee also the Annales des Sciences Naturelles, t. xiv. p. 118-122, and 

 von Dechen, Geognosie, s. 553.) Amongst the most striking proofs of 

 the transformation of rocks by plutonic action, we must place the belem- 

 nites in the schists of Nuffenen (in the Alpine valley of Eginen and in 



