appropriate mixture of quartz and carbonates. The pres- 

 ence of fresh diallage is quite in keeping with the rock last 

 described. The conclusion seems justified that the rock 

 studied by these authors was a peridotite with porphyritic 

 diallage. The green and brown rock mentioned as occurring 

 with the chromite-anorthite rock is also proved to be an 

 altered dunite. A section of a green and white rock 

 examined microscopically was composed of finely divided 

 quartz clouded with talc stained green (by chrome oxide ?), 

 and large areas of cloudy dust-like carbonates, extending 

 into long bands separating the quartz-talc material into 

 roughly rounded areas and containing limonite. 



Picotite also occurred surrounded by a green-stained 

 area. Graduations from this rock were also found. They 

 occur in the most exposed positions and are the final stages 

 in the alteration of a peridotite. This all confirms the 

 opinion expressed by the Rev. J. Milne Curran, that " the 

 ehromite (picotite) occurred in mueh altered terpentine, or 

 closely related ultrabasic rock." 1 



[Note added while this paper was passing through the 

 press. Prom Mr. Arthur Coombe, I have received a speci- 

 men of an exceptionally coarse grained gabbro from Dundas. 

 It is an olivine gabbro, in which the felspar is bytownite,and 

 the olivine has been converted into a quartz-mosaic, with 

 a little dusty carbonate. Surrounding the olivine was 

 pyroxene, converted almost entirely into chlorite, and con- 

 taining an intergrowth of pleonaste in the manner described 

 previously. Some diallage crystals pass into a single 

 pseudomorphous crystal of chlorite.] 



Included Rocks of Dundas other than Plutonic. 



Olivine dolerite. — This rock is rather rare; it has been 

 found in the basalt in just the same way as the plutonic 



1 Geology of Sydney and the Blue Mountains, 1898, p. 262. 



