156 GREAT SERPENTINE BELT OF NEW SOUTH WALES, iv., 



micrographic intergrowth with the felspar. In the last case, 

 there can be no doubt that the quartz is primary. The larger 

 grains apparently replace portions of the felspar-felt, and in no 

 way resemble corroded phenocrysts, but have more the appear- 

 ance of secondary introductions, especially when they occur in 

 zones characterised by more than the usual amount of calcite or 

 chlorite. Finally, in several of the rocks the quartz-grains are 

 completely surrounded by chalcedony, which extends outwards 

 into the felspar of the rock-matrix. This is clearly a secondary 

 enlargement of the quartz-grains, and we may note at the same 

 time, the abundance of chalcedony in the vesicles of some of the 

 rocks. Chlorite and calcite also occur in the vesicles either 

 singly, or in association with each other. 



The Post-Peridotitic Dolerites.. 



These rocks form dykes in the serpentine, chiefly on the 

 northern slope of Chrome Hill, and also in a small patch of 

 serpentine that occurs west of the Peel River, south of Warden's 

 homestead. They are usually very crushed and altered. The 

 freshest rock(1107) has a very peculiar structure It is partly 

 granulitic, the base consisting of angular or rounded grains of 

 augite in a groundmass of platy felspar. There are a few large 

 felspar-phenocrysts, and some ophitic glomeroporphyritic aggie- 

 gates of felspar and augite, as well as isolated grains and crystals 

 of augite. The pyroxene is pale in colour, and though there is no 

 noticeable purplish tinge, hour-glass structure may occasionally 

 be seen. The optic axial angle 2V is 51°. No difference is 

 observable between the augite of the phenocryst and that of the 

 smaller grains. Both are very fresh, though chlorite is abundant, 

 at times pseudomorphous after augite. The plagioclase is not 

 easily determinable. Some large zoned crystals occur, showing 

 refractive indices greater than that of Canada balsam, but the 

 extinction-angles do not yield determinative readings. The 

 felspar of the groundmass is very dusty, and is frequently de- 

 composed to a cloudy mass of epidote and clinozoisite. It seems 

 to have the optical characters of an acid andesine. The com- 

 position calculated from the chemical analysis (see p. 139) is 



