MANUAL OF NATURAL HISTORY. 545 



Swedish iron is procured from rocks of this class, 

 forming mountain-masses in Smoland ; as is also the 

 Elba, or opercular iron. Manganese has been also 

 procured from the rocks of this group ; and in gneiss 

 and mica-schist, the most important copper-ore (or 

 pyrites) occurs on the Continent, and in Cornwall 

 and Ireland ; lead, in the form of galena, or bisul- 

 phuret, is present in these rocks, as well as in 

 the fossilliferous deposits ; silver, as a bisulphuret, 

 is found in green-stone, clay-slate, and syenite, the 

 veins sometimes extending, as in Mexico and Peru, 

 to the ordinary deposits. Tin, in the shape of 

 binoxide, occurs in granite, and in " killas/' a pecu- 

 liar schist in Cornwall, and in other parts of the 

 world ; mercury is occasionally detected dispersed 

 in globules in granite, but the rich ore of this metal, 

 cinnabar, is from the primary or grauwacke strata 

 of Almaden, in Spain ; antimony and molybdenum 

 are also found in granite, gneiss, and mica-schist; 

 and gold has been found disseminated in quartzose 

 and chloritic rocks in Brazil, and in various parts 

 of the earth it is extracted from auriferous sands, 

 produced by the decomposition of these strata, as 

 are likewise platinum and diamonds. Flexible 

 asbestus, or amianthus, is found among the mica- 

 schists, as are also garnets; and some of the lime- 

 stones produce valuable marbles. 



II. CLASS.— PALAEOZOIC-FORMATIONS. 



The different groups composing this class have, 

 until of late years, been arranged partly with what 



