ON THE FORMATION OF CRYSTALLINE ROCKS. 273 



even possessing the characteristic odor of the petroleum of Bechel- 

 bronn. In this way we can understand the presence of bitumen in 

 some concretionary metalliferous veins, (Derbyshire, Camsdorf, Raibl 

 in Carinthia.) 



In short, the bitumens are probabl}'' derived from vegetable sub- 

 stances;* they appear not to be the products of a simple dry distilla- 

 tion, but to have been formed with the co-operation of water, and 

 perhaps under pressure; graphite would be but the most exhausted 

 product of these substances. t These different combinations of car- 

 bon are connected with the transformations which are going on in the 

 interior of rocks, probably under the influence of a high temperature. 

 The activity, and even the violence, sometimes capable of producing 

 a slight earthquake, with which the disengagement of carburetted 

 hydrogen takes place in Tauris, on the borders of the Caspian sea, 

 and in the environs of Carthagena, in South America, prove that the 

 causes which have formerly isolated bitumen are still in activity. 



CHAPTER V. 

 METALLIFEROUS DEPOSITS IN THEIR RELATION TO METAMORPHISM. 



Metallic combinations, derived from the interior of the earth, are 

 very frequently accumulated in the clefts which exist in the strata, and 

 have formed metallic veins. Sometimes also these and the various 

 other combinations which accompany them are diffused through the 

 rocks, and in penetrating them have caused them to undergo very 

 decided transformations. It is thus that the masses of specular iron 

 of Framont, the deposits of the Banat, of the environs of Christiania, 

 and of Turjinsk, have been introduced in the neighborhood of erup- 

 tive rocks. In these localities the metallic minerals have been inter- 

 mingled with silicates, produced at the same time with them in the 

 sedimentary rock itself. In this way tin has been introduced in many 

 of the formations where it is now found, reacting profoundly on the 

 surrounding rocks, as I long ago pointed out, and forming in those 

 rocks characteristic minerals. 



When entire masses of rock have undergone transformations, it 

 sometimes happens that, over vast extents, metallic substances have 

 been lodged between their lamellfe, under such circumstances that 

 it is impossible to resist the idea that their presence has been inti- 

 mately conn(fcted with the very cause which produced the metamor- 

 phism. As an example, I mention gold associated with iron pyrites 

 or with mispickel at Zillerthal in the Tyrol, at Galicia in Spain, 

 where it is also accompanied with tin; but it is especially in the Oural, 



- Although Berthelot and other chemists have been able by ingenious methods to 

 obtain by synthesis the compounds which are called organic, nothing authorizes us for the 

 present to believe that this can be done for the bitumens. 



f Graphite and bitumen are associated in Java in the neighborhood of volcanic forma- 

 tions, and with lignite in a tertiary formation, from which jets of carburetted hydiogeu 

 escape. 



18 



