BY W. N. BENSON. 717 



bonate replacements of their ferromagnesian minerals, andesites, 

 porphyritic, noncrystalline, or more or less glassy, vesicular 

 or even pumiceous, with the cavities filled with calcite and 

 chlorite; basalts, vesicular or glassy, differing from the andesite 

 only in the amount of magnetite; augite-diorite porphyries, as 

 described by David and Pittman, with phenocrysts of plagioclase, 

 orthoclase, augite, and sphene in a greyish felsitic ground-mass (in 

 hand-specimen, this rock resembles the malchites of the Nundle 

 district, but the microscope shows it to be distinct, and allied to the 

 Tamworth tuffs) ; dolerite containing granophyric quartz, and 

 very similar to the rock of Hanging Rock, near Nundle; chert, in 

 large or small angular fragments, often radiolarian; limestone, 

 either in dense blue rocks or more crystalline, sometimes contain- 

 ing fossils, as Heliolites, Syringopora, Stromatopora and crinoid- 

 stems, or indeterminable traces of microscopic forms; and numer- 

 ous, isolated crystals or fragments of felspar, quartz, and augite. 



These rocks rest directly on radiolarian rocks at Tamworth ; they 

 rest on, or are interbedded with the same cherts west of Bingara; 

 they contain interstratified bands of chert with radiolaria, or, as in 

 Cobbadah Creek Gorge, fine-grained tuffs, composed of minute 

 felspar-laths with pyroxene, and secondary chlorite and prehnite 

 in a very finely granular ground-mass of quartz and felspathic 

 material, which also contains some radiolarian casts. In three 

 localities, flows of porphyritic spilite-lava have been found, inter 

 bedded in these agglomerates. 



(4) The Barraba Series consists of mudstones, tuffs, breccias, and 

 limestones. The mudstones and claystones do not differ in micros- 

 copical character from those of the Tamworth Series, to any great 

 amount. The chief changes are in the coarse grain of the majority 

 of the series, and in the abundance of narrow bands of felspathic 

 tuff. The rocks are well bedded, and consist of fragments of quartz 

 and felspar, with a little chlorite and an irresolvable base, the 

 whole stained more or less with iron-oxide. Carbonaceous matter 

 may, or may not, be present. In certain rocks, it is very abundant. 

 The tuff is interlaminated, usually in very thin bands, perhaps 



