Ch. V.] PRIMARY SCHISTOSE ROCKS. 87 



remarkable on the Italian side of the Alps. Almost all these 

 varieties of micaceous and talcose slates exhibit different tints 

 of green, sometimes resembling that of chlorite : they very 

 seldom contain distinct scales of mica or talc ; but their sur- 

 face is always more or less glossy, and often presents a striated 

 and somewhat fibrous appearance. 



This talc-schist forms the basis of the formation; and, 

 by its combination with other minerals, gives rise to distinct 

 species of rocks. Crystals of felspar are sometimes uniformly 

 disseminated throughout it ; when these are of a large size, 

 the rock resembles a variety of gneiss : generally, however, 

 they are very small, and often scarcely discernible, except on 

 the cross fracture of the rock ; and even then this mineral 

 would not be recognised, but by tracing its gradual increase 

 in size till it forms distinct crystals. Quartz is rarely present ; 

 and when it is visible, it occurs as small grains scattered about 

 in very irregular groups. Hornblende is no where to be met 

 with in this series; that is, in a distinct crystalline form: 

 but it is undoubtedly sometimes mixed with these rocks, for 

 hornblende rocks are found associated in the same mass with 

 felspathic talc-schist, passing into each other by insensible 

 gradations. 



The transitions of all these rocks into each other lead one 

 to conjecture, that their different degrees of hardness and 

 tenacity must be attributed to the presence of one or other 

 of these accessary minerals. When they are tough, and at 

 the same time hard, hornblende may be suspected to exist in 

 the compound ; when they are very hard, and yet easily fran- 

 gible, quartz is probably predominant; and, lastly, when 

 they are sufficiently tenacious to be indented by the hammer 

 without breaking, but are not so soft as to be cut by the 

 knife, the presence of felspar is indicated. 



Such are the principal talcose rocks of this district : and in 

 those places where they are best characterised, and most 

 abundant, will be found serpentines, either pure or blended 

 with limestone, fine-grained hornblende rocks, crystalline 



G 4 



