582 GREAT SERPENTINE BELT OP NEW SOUTH WALES, ii., 



Point, they contain very coarse pegmatitic veins of a composition 

 similar to their own. Their relation to the spilite-lavas, in the 

 field is often very perplexing; at times, they certainly intrude into 

 the spilite, elsewhere the spilites appear to intrude into them. 

 Sometimes, in hand-specimens, it is difficult to say which is which, 

 the dolerite assuming a vesicular character. This was all the more 

 confusing, as at the time of surveying, it was believed that the dole- 

 rite was subsequent to the peridotite(15), on account of the apparent 

 intrusion of dolerite into peridotite, especially on the north slope 

 of Chrome Hill. Work in the northern regions, and subsequent 

 microscopic studies have shown this is not the case. The dolerite 

 is related to the spilites, and is older than the ultra-basic rock. The 

 mass of dolerite, in the peridotite alluded to, must have been torn 

 off the adjacent dolerite-mass invaded by the peridotite. Peno- 

 logical investigation shows that the rock has the structural charac- 

 ters of ordinary dolerite, except that the plagioclase varies from 

 andesine, the usual type, to oligoclase albite in the Hanging Rock. 

 Occasionally, specimens show a slightly gneissic flow-structure, 

 notably some near Red Rock, which overlooks Munro's Creek (Plate 

 xxiii.). This series of intrusions probably took place during, or 

 shortly after, the deposition of the Bowling Alley Tuff-breccias, 

 claystones, and spilite-flows. The abundance of dolerite, and 

 absence of agglomerate, in this region, together with the abundance 

 of agglomerate and rarity of dolerite in other regions, suggests 

 that the same igneous activity might have had subterranean expres- 

 sion in the one case, superficial in the other. 



5. Following the dolerite-intrusion, and deposition of the Nundle 

 Series, there was a great earth-movement, a thrust from the 

 E.N.E., which developed the persistent fault-plane separating the 

 Woolomin and Bowling Alley Rocks. The peridotite was intruded 

 into this plane during the movement. (The evidence for this state- 

 ment will be discussed later.) Microscopic examination of the 

 rocks proved them to be derived chiefly from hartzbergite, with a 

 minor amount of herzolite and dunite. Generally the rock had a 

 fairly even grain-size of about 2 mm., in diameter, but here and 

 there, particularly on Chrome Hill by Bowling Alley Point, the 



