248 Outlines of Geology. 



upon which the other stratified materials have been successively 

 deposited in that order of arrangement which we have enu- 

 merated ; or whether the stratified rocks are to be considered, 

 with the Huttonians,as primary, and the granitic and other masses 

 that we are about to examine, as having been subsequently ele- 

 vated by the expansive force of subterraneous heat, are questions 

 that have eagerly engaged the contending geological schools, and 

 to which too much importance has often been assigned. As we 

 proceed in the examination of these substances, we shall notice 

 such of their characters as have especially given rise to the igne- 

 ous and aqueous sects ; but, as heretofore, I shall consider hypo- 

 theses and theories as very subordinate objects. 



Under the term granitic formation, I include, not merely granite, 

 properly so called, but the substances into which it merges, either 

 from the predominance of one or other of its ingredients, from 

 the loss of one or other of them, or from the occasional addition 

 of some new mineral ; and I shall also include in this division of 

 rocks, those substances which are their occasional accompani- 

 ments ; such as serpentine, marble, and primary conglomerates : 

 rocks always, and exclusively, associated with the granitic series, 

 and unknown amongst those formations in which organic remains 

 are to be found. 



Under the generic term granite, we include all crystalline aggre- 

 gates of quartz, felspar, and mica. Quartz, or siliceous earth, 

 known in its crystalline form under the name of rock-crystal, 

 has already been denned. (Vol. XIX. p. 80.) 



Felspar is an alumino-siliceous compound, containing a portion 

 of alkaline matter, and frequently coloured by oxide of iron, 

 which gives it various shades of brown and red, and of which the 

 foliated, the green, the blue, and iridescent variety of Labrador 

 are leading sub-species. When crystallized felspar affects a four 

 or six sided prismatic form, fusibility before the blow-pipe, 

 and a texture somewhat softer than quartz, but yet hard enough 

 to scratch glass, are its further distinctive properties. 



Mica, the last component of granitic aggregates, contains, as 

 its chemical constituents, silica, alumina, and a little magnesia 



