300 Felations of Trap-Bocks with Ores of Copper. 



relations of ores are so numerous that a true law of position 

 {gisemenf) results from them ; and if we point out the metal- 

 liferous repositories in a country, nothing is more rational 

 than the questions : What are the eruptive rocks to which 

 the ores are suhordinate ? What are the particularities of 

 their relations ? 



In a former work (^Etudes sur les Mines, 1844), we have ex- 

 plained the eminently metalliferous characters of the serpentine 

 formations of Tuscany, referring the numerous cupriferous and 

 ferriferous repositories of the country to these rocks. In the 

 present case, we propose to prove, that these relations are 

 not exceptional ; that many trappean rocks present analogies 

 with those of Tuscany, in the nature of the rocks of contact, 

 and in the ores of copper and iron which are connected with 

 them. Let us, in the first place, state, in a few words, the 

 general conditions of the serpentine formations of Tuscany, 

 and of the subordinate minerals. 



From Savona, in the Gulf of Genoa, to beyond Monte Ar- 

 gentario, the serpentines form the principal features of acci- 

 dentation in the littoral chain which thus traverses the terri- 

 tories of Genoa, Modena, Lucca, and Tuscany ; throughout the 

 greatest part of its course this is called a metalliferous chain. 

 The characters of the serpentines are eminently eruptive in 

 the composition and in the forms of the masses, and particu- 

 larly in the circumstances of upraising and alteration, which 

 they have produced in the rocks traversed. The rocks of con- 

 tact, designated by the general name o^gabbro, may be divided 

 i^;ito two classes, the green and the red gabbro. 



The red gabbro are in some measure the first rocks of con- 

 tact which have been remarked and signalised as metamor- 

 phic. Their red colour, which is owing to a considerable 

 quantity of earthy oligistic iron, forms a contrast with the 

 ordinary colours of the sedimentary formations of the country, 

 and with the serpentines themselves. There is no trace of 

 stratification in the true gabbro-rosso ; its structure is often 

 brecciform, and green steatitic fragments may be distin- 

 guished among the red fragments which predominate ; often 

 also, pyroxene and calcareous spar are met with in it. 



