224 



guished, by their crystalline texture, from the 

 secondary, which are, on the contrary, said to be 

 characterized by a compact texture and earthy 

 aspect. But this observation is perfectly errone- 

 ous ; as limestones of an earthy, and of a com- 

 pact aspect, occur among the primary; arid, 

 although perhaps more rarely, the most perfect 

 crystalline limestone is sometimes found among 

 the secondary strata. 



The difficulty between the compact felspar 

 associated with gneiss, and therefore primary, and 

 that which is found with the overlying rocks, is 

 of little moment ; as the former is rare, and is ge- 

 nerally so intimately connected with its associates 

 as to be necessarily referred to its proper place. 



With respect to jasper, chert, and siliceous 

 schist, which the geologist will often find among 

 the primary rocks, it will hereafter be seen that 

 they occur in both classes; for which reason 

 they have been separated and placed in a distinct 

 division, so as to render any remarks on them 

 unnecessary in this place. 



"; -The difficulties that regard porphyry and its 

 associates, are stated at length in the preliminary 

 remarks on the overlying rocks. 



