540 THE GKOLOGY OF NEWBRIDGE, NEAR BATHURST, N.S.W., 



in a northerl}' direction. In hand-specimen this rock is not 

 unlike the green slates, though greyer and more fibrous; and its 

 cleavage is poor. Its distinguishing feature is the presence of 

 numerous blebs of clear quartz up to one-eighth of an inch in 

 diameter. These grains are nearly round or lenticular, but have 

 rough surfaces and are not smooth as if waterworn. Micro- 

 scopically it is very like the green slate, and shows the rock- 

 flowage structure slightly developed among the small quartzes, 

 and parallel disposition of the biotite, which is partly chloritised 

 with the formation, in some cases, of haematite. Sericite occurs, 

 and comparatively large crystals of a twinned plagioclase, pro- 

 bably oligoclase, which contain inclusions of biotite and sericite 

 arranged in lines parallel to the general direction of schistosity. 

 In another specimen of Augen Slate the felspar appears to be 

 albite. Pju-ites occurs in some instances, rutile and zircon usually. 

 Tourmaline is rare or absent. Muscovite is sometimes present, 

 usually inclined to the direction of schistosity. The quartz blebs 

 may be either of one optically continuous grain, or of several 

 grains of different orientation. The lines of biotites may be 

 truncated by the quartz blebs, or may bend round them, or more 

 rarely pass into them. The boundary of each quartz bleb is not 

 a smooth curve, but irregular. 



With regard to the mode of origin of the Augen Slates, 

 Curran* terms them conglomerates, and points out that, as the 

 limestones, representing coral-reefs in the old Silurian sea, were 

 doubtless near the shoredine, the Augen Slates, which are 

 generally in the neighbourhood of the limestones, will represent 

 the beach-conglomerates. While this may in part account for 

 the large quartz grains, I am inclined to believe that they are 

 chiefly due to shattering and subsequent recrystallisation under 

 pressure. The larger quartz grains would resist the crushing 

 more than the other grains, or would be broken up only on their 

 surfaces; and during the recrystallisation the large grains would 

 grow at the expense of the smaller. The surface of the blebs is 



"^ These Proceedings, 1891 (2), Vol. vii. p. 198. 



