BY W. N. BENSON. 665 



The more altered rocks are far more common. In these, the 

 augites are generally changed to chlorite, with the development of 

 much carbonates; more rarely they pass into fibrous amphibole. 

 The felspars are frequently too decomposed for determination, and 

 have been changed to paragonitic mica sprinkled with epidote. If 

 the specimen has come from the eastern side of the serpentine-line, 

 it is usually crushed and sheared, and veins of quartz, paragonite, 

 epidote, or rarely prehnite may have been introduced. In other 

 rocks, there is a varying amount of glassy residuum, with crystal- 

 lites of magnetite and felspar, and giobulites probably of augite. 

 In others, the glass appears to be devitrifying. Felspar and 

 augite are the main constituents, the former usually very altered, 

 clouded with secondary mica, but when fresh it is usually very 

 acid. Magnetite varies exceedingly in quantity, from great abund- 

 ance to complete absence. It contains most of the titanium in the 

 rock, as the augite is rarely purplish. A single pseudomorph, 

 doubtfully referred to olivine (bowlingite), is the only approach 

 to an indication of that mineral. 



Porphyritic spilites are less abundant. One [M.B., 50], which 

 occurs on the upper Bingara track, six miles south of Bingara, 

 is quite free from magnetite. It contains felspar-phenocrysts 

 (oligoclase albite), 3 mm., in diameter, in a very finely granular 

 augite and felspar ground-mass. The spilite-flow in the agglomer- 

 ates on Anderson's Creek [M.B., 17] contains large phenocrysts of 

 andesine, but with a hypocrystalline base filled with microlites of 

 felspar, augite, and magnetite. In one southern rock [N.T., 277] 

 the phenocrystic constituent, augite, is completely changed to 

 actinolite. 



The hypocrystalline types are best exemplified by the lava 

 [N.T., 31] which flowed over the coral-reef, now forming the lime- 

 stone on Moonlight Hill, south of Nundle (See p. 575). This is an 

 excellent instance of skeleton-crystallisation. Magnetite has formed 

 in small plates, standing perpendicularly out from the felspar 

 microlites and from the long, ropy masses of dusty material, 

 augite-globulites and carbonates (?), while there is some glassy 

 background. The few larger felspar-crystals, with their swallow- 



