240 



A NATURALIST IN THE PACIFIC 



CHAP. 



III. Class. — Hypersthene-Augite Rocks {Plag., 



JiypcrstJi.-aug.). 



Sub-class. 



Order. 



1. 



No groundmass {non-matr. 

 Gabbros, in part. 



Groundmass [matr.) 

 Pyroxene-andesites, in part. 



Represented by the Hypersthene-gabbros in 

 collection. 



f 1. 



Felspar lathes not in flow-arrangement {non-Jlit. ). 



Felspar lathes in flow-arrangement {flu.). 



3- 

 Felspars of the groundmass short and broad 

 (orthophyric, orth.). 



Groundmass granular or presenting a mosaic 

 (felsitic, feh. ). 



IV. Class. — Hypersthene Rocks. 

 V. Class. — Hornblende-Hypersthene Rocks. 

 VI. Class.— Quartz-Hornblende-Hypersthene Rocks or 

 Dacites. 



These last three classes are merely provisional. They include 

 the Acid Andesites of Vanua Levu, which are all characterised by 

 the prevalence of rhombic pyroxene amongst the phenocrysts and 

 by its predominance or rather by its usually exclusive occurrence 

 in the groundmass. All the classes are capable of being split up 

 into two sub-classes and four orders as in the case of the third class. 

 The characters of these rocks are given in Chapter XXI. 



VII. Class. — Hornblende Rocks. 



In this class are included those rocks where hornblende is the 

 only ferro-magnesian mineral. It is only represented by two 

 diorites described on page 251. 



VIII. Class. — Oligoclase-Trachytes. 1 ^ .. , . 



,„ „ ^ Described in 



IX. Class. — Quartz-porphyries and \ -, XXI 



Rhyolites J 



