74 



agencies. In the Continental system of classification these terms are applied 

 to the pre-tertiary representatives of the post-cretaceous dolerites, basalts 

 and andesites. 



The effects of contact and regional metamorphism on rocks of Group B 

 have been studied only in a few cases. They will be described in the 

 following pages, but no attempt is here made to tabulate the results already 

 obtained. 



GROUP C. 



ROCKS IN WHICH ORTHOCLASE IS ABUNDANT. PLAGIOCLASE USUALLY 

 PRESENT. NEPHELINE AND LEUCITE ABSENT. 



() Without quartz ', 



I. ORTHOCLASE-HORNBLENDE ROCKS. 



(a) Granitic texture. Syenite (Werner). 



(b) Trachytic texture. Hornblende-trachyte (l} and-felsite. 



II. ORTHOCLASE-AUGITE ROCKS. 



(a) Granitic texture. Augite- syenite. 



(b) Trachytic texture. Augite-trachyte andfelsite. 



III. ORTHOCLASE-MICA ROCKS. 



(a) Granitic texture. Mica-syenite or minette.^ 

 (V) Trachytic. Mica-trachyte and -felsite. 



IV. ORTHOCLASE-MlCA-HoRNBLENDE RoCKS. 



(a) Granitic texture. Mica- hornblende- syenite. 



(b) Trachytic texture. Mica-hornblende-trachyte and -felsite. 



(ft) With quartz. 



(a) Granitic texture. 



(1) ORTHOCLASE-QUARTZ ROCKS. Aplite. 



(2) ORTHOCLASE-QUARTZ-BIOTITE ROCKS. Granitite (Rose). 



(3) ORTHOCLASE-QUARTZ-HORNBLENDE ROCKS. Hornblende- 



granite. 



(1) There is, perhaps, no term in petrography which has been more widely used than 

 trachyte. In the present work it is employed as a general term connoting a trachytic texture 

 (i.e., not granitic or granito-porphyritic), and the presence of glassy orthoclase (sanidine). Where 

 the felspar is not glassy (orthoclase proper), the term felsite will be used in the same general 

 sense. Sanidine is frequently associated with a glassy base, and orthoclase proper 

 is usually associated with a micro- or crypto-crystalline groundmass. 



(2) The term minette has been applied both to the granitic and trachytic varieties of this 

 group. In the present work it will be applied only to the former. 



