692 GREAT SERPENTINE BELT OP NEW SOUTH WALES, iii., 



microscope, however, shows that it must be a dyke later than 

 either. 



The presence of albite-bearing dykes, in the serpentine, calls 

 for some remark. Prof. Lacroix(28) instances dykes similar to 

 the above, accompanying the ultrabasic rocks, in support of his 

 contention that the ultrabasic magmas gave out alkaline emana- 

 tions. The " granite " of Gew Graze, at the Lizard(40), which is 

 changed locally into pseudophite, is very similar in microscopical 

 appearance, and contains identical needles of pale green pennine. 

 Similar rocks again occur in the Serpentine Belt at Narsatas 

 Hill, Siberia, where it was found by Dr. J. M. Bell. The slices 

 studied were found in the collection of Dr. Bonney, by whose 

 kind permission they are here noted. The association of serpen- 

 tine with sodic solutions may possibly account for the production 

 of glaucophane in the sediments altered by the intrusion of the 

 peridotite at Angel Island, Calif ornia(*9). 



(8). So far as they have been examined, the dolerites and 

 dolerite-porphyrites of the Blue Knob group of intrusions are a 

 fairly homogeneous series of rocks within certain limits. They 

 are quite different in character from both the older dolerites, and 

 the post-peridotite group of rocks, and are probably younger than 

 either. 



The typical dolerite of the Blue Knob laccolite [M., 312] is a 

 medium-grained rock, composed chiefly of idiomorphic labradorite, 

 which is strongly zoned, and clouded with epidote and probably 

 zoisite. With this is a large amount of idiomorphic augite, partly 

 quite fresh and pale yellow in colour, but, in the main, completely 

 decomposed to bright yellow-green chlorite. Large grains of 

 ilmenite are abundant. Between the crystals, there is a small 

 amount of more finely crystallised matter. This consists of 

 quartz, decomposed felspar, and abundant, small crystals of 

 apatite, which mineral does not occur in the plagioclase-pheno- 

 crysts, except in their outer edges. 



The porphyrites occur in the narrower intrusions, dykes, and 

 sills. As typical of these, M.B.,326, may be described. It occurs 

 on the main road, two miles south of Cobbadah. It is a hand- 

 some rock, with a fine-grained, dark green ground-mass, a few 



