72 



II. PLAGIOCLASE-PYROXENE ROCKS. 

 (a) With Olivine. 



(1) Plagioclase-augite-olivine rocks. (2) 



(a) Granitic texture. Felspar and augite both in the form of 

 coarse grains. Olivine- gabbro. 



(6) Texture intermediate between the granitic and trachytic. 

 Felspars lath-shaped in section. Augite in crystals, grains, 

 or irregular plates (ophitic). Olivine- dolerite. 



(c) Trachytic texture. Finely crystalline or compact ; often 

 containing a certain amount of amorphous matter. Felspars 

 giving lath-shaped sections. Augite of the groundmass 

 in small crystals or granules. Olivine-basalt. 

 (2) Plagioclase-enstatite (3) -olivine rocks. 



(a) Granitic texture. Olivine-norite. 



(b) Trachytic texture. (Not recognised). 



(ft) Without Olivine; without quartz. 



(1) Plagioclase-augite rocks. 



(a) Granitic texture. Gabbro.^ 



(b) Texture intermediate between the granitic and the trachytic. 



Dolerite. {5) 



(c) Trachytic texture. Basalt; and, in some cases, augite- 



andesite. 



(2) Plagioclase-enstatite rocks. 



(a) Granitic texture. Norite. 



(b) Trachytic texture. Enstatite-andesite. 



(3) Plagioclase-augite-enstatite rock. 



(a) Granitic and intermediate textures. Enstatite-gabbro and 



enstatite-dolerite. 



(b) Trachytic texture. Enstattie-augite-andesite. 



(7) With quartz ; without olivine. 



(a) Granitic and intermediate textures. Quartz-gabbro and 



quartz-dokrite (quartz-diabase of Continental authors). 



(b) Trachytic texture. Quartz-augite-andesite. Dacite (in part). 



(2) The term augite is used as the general name for the monoclinic pyroxenes. It includes 

 diallage and pseudo-hypersthene. 



(3) It must be remembered that the term enstatite is here used to cover the entire 

 group of rhombic pyroxenes. 



(4) When the felspar is anorthite the rock is termed eucrite. 



(5) Continental authors use the term diabase for all pre-tertiary rocks having this com- 

 position and texture. As we find no constant original differences between the pre-tertiary and post- 

 cretaceous rocks of the basic group in this country it is impossible for us to adopt the Continental 

 system of classification. 



