BY W. N. BENSON. 709 



The intrusion of granite into this series has further complicated 

 matters, by providing a number of very interesting metamorphic 

 rocks. 



The clay-shales and mudstones of the series have been described 

 by Professor David and Mr. Pittnian, from the railway-cuttings 

 east of Tamworth. They consist of very finely divided quartz 

 with biotite, chlorite, and a little carbonaceous matter, with some 

 iron -staining ; felspar is present in some amount; sometimes, it 

 may be of secondary origin. Occasionally, tourmaline and apatite 

 are present, but rutile is remarkably rare. Frequently, the layers 

 of deposition are very well marked. Radiolaria are present, in 

 some specimens, in enormous abundance, about one million to the 

 cubic inch, according to the above authors. Occasionally, they 

 can be seen with a pocket lens, or even with the naked eye. The 

 rocks are fine-grained, and evenly interbedded with bands of sub- 

 marine tuff. 



The cherts are banded light and darker green in colour, as a rule, 

 though sometimes black. Very little can be determined from these 

 in microscopical examination; they are more or less completely 

 made up of radiolaria. Pressure has frequently forced all these 

 into an oval shape. The material of the radiolaria is chiefly chal- 

 cedony, while the ground-mass of the rock contains finely granular 

 quartz, felspar, epidote, and carbonate with or without carbonace- 

 ous matter. Analysis of a black chert showed that it contained 

 91-06 per cent, of silica(3, p. 32). These cherts are intimately 

 mixed with tuff; and the peculiar entanglement of chert and tuff, 

 figured by Professor David and Mr. Pittman, is repeated all along 

 the horizon of the cherts. In the neighbourhood of Horsearm 

 Creek, Attunga, these rocks have been metamorphosed by the in- 

 truding granite. A considerable variety of specimens may be 

 obtained, but few have been studied as yet. It has been consider- 

 ably recrystallised, and is now a mosaic of quartz and acid felspar, 

 chiefly water-clear albite, dotted with numerous, small, brown bio- 

 tite-flakes. The aluminous portion of the rock has been segregated 

 into needles of sillimanite, pale brown in colour, and very abun- 

 dant. A little magnetite is also present. 



