196 



The variety of lively or peculiar colours which it 

 presents, generally affords a good empirical cha- 

 racter. It is commonly simple ; with an uniform 

 fracture, imperfectly conchoidal and splintery ; 

 but some varieties have an indistinct granular 

 fracture, and others are even formed of small 

 lamellar concretions. The broken surface is al- 

 most always dull and earthy ; but it frequently 

 contains natural irregular joints, with polished 

 surfaces having an unctuous aspect and feel. The 

 hardness is so various as to afford no distinction ; 

 as it sometimes resists the knife, when, at others, 

 it can be scratched with great ease. The fre- 

 quent presence of steatite, asbestos, and talc, 

 forms an empirical mark which may also be of 

 use to beginners. Moreover, it is not stratified. 



GNEISS. 



Is composed principally of the same ingre- 

 dients as granite, under the same license; but 

 there are some varieties in which clay slate, and 

 chlorite slate form constituent parts. It is dis- 

 tinguished from granite by a parallel position 

 which pervades the mica, most generally; or the 



