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



The breccias are generally greenish in colour, and consist of 

 finely divided, volcanic material, with large, angular pieces of 

 radiolarian chert, which are not infrequently much bleached around 

 their edges. A few limestone-fragments are sometimes present. 

 The igneous fragments consist of finely crystallised, vesicular, or 

 hypohyaline spilites and andesites, which are sometimes little 

 more than pumice. The vesicles of the pumice are filled in with 

 calcite, chlorite, and epidote. There are also crystals and grains 

 of plagioclase and augite, that might have been derived from a 

 dolerite, rounded or angular fragments of quartz, rarely a little 

 orthoclase. 



The chief difference between the breccias and the tuffs is that 

 the latter are finer-grained, and more usually consist of single 

 minerals than rock-fragments. On the other hand, by increase in 

 size of the fragments, the breccias pass into the agglomerate-type. 

 Radiolaria are sometimes present in these rocks, occasionally per- 

 fectly preserved. 



The tuffs are more rare in the Tamworth Series than the breccia, 

 but are more important in the rocks of the Nun die Beds ; they are 

 greyish or brownish in colour, with an even, medium grain-size, 

 with occasionally larger felspars. They consist of fragments and 

 crystals of andesine, augite, which is decomposing to actinolite 

 and chlorite, less commonly quartz, also fragments of chert, and 

 pilotaxitic and hyalopilitic spilite with chlorite-filled vesicles. The 

 ground-mass consists of finely divided material of the same com- 

 position. Occasionally, radiolarian casts are observable. Mag- 

 netite, pyrites, epidote, and carbonates are developed to a varying 

 amount. The tuffs differ from one another in the amount of augite 

 and quartz, the perfect crystal-outline, or the fractured or rounded 

 nature of the mineral-grains, the proportion between base and 

 large grains, and the nature of the volcanic rock-fragments. In 

 one tuff, occurring with the limestone at Attunga(M.B., 147), the 

 volcanic fragments are of an extremely basic glass, crowded with 

 dusty magnetite and felspar-microlites. A similar inclusion has 

 been observed in the breccia near Bingara. There are, in addition, 

 a few fragments of the usual type of lava and radiolarian chert. 



