BY W. N. BENSON. 679 



with grains of carbonate, and the disposition of the abundant 

 magnetite-dust suggests the former presence of bastite. 



(8). The silicated rocks are also widespread. They are best 

 developed at the head of Oakenville Creek, near Nundle, at the 

 head of Munro's Creek, and the mouth of Sheep Station Creek 

 valley, near Bowling Alley Point. While silicification may occur 

 with carbonation, it is often quite a separate process. In the 

 Sheep Station Creek rocks, normal, partly sheared bastite-serpen- 

 tine passes into isotropic opal, and becomes veined, small open- 

 ings are dissolved out, and these become lined with radiating 

 chalcedony [N.T., 130]. In the further altered rocks, such as 

 those of Oakenville Creek, the greater part of the serpentine may 

 be dissolved away. The magnesia is removed, and the iron 

 remains as limonite-powder, in the meshes of a network of large 

 and small silica-veins, with vughs lined with chalcedony and 

 quartz-crystals. In fact, a regular sinter is produced. In some 

 of these " vughs " the magnesite is deposited in dense white, 

 roughly mammillated masses. Particularly fine specimens of 

 chalcedony, in mammillated or stalactic form, used to be obtained 

 on Dangar's Gully, a tributary of Oakenville Creek. 



In Spring Creek, about two miles south of Moonbi Railway 

 Station, is an opaline sinter, passing into massive, white opal, 

 stippled with small dendrites [N.T., 471]. 



Non-sin tery, secondary silica-rocks are also divisible into mas- 

 sive and schistose groups. Among the massive types are some 

 pyritous chalcedony-rocks, products of extreme silicification, 

 associated with the carbonate rocks of Folly Creek[N.T., 181,182], 

 These appear to contain finely divided talc. The rocks between 

 this point and Munro's Creek consist, of bottle-green opal with 

 white veins, and a considerable amount of talc. The haematite 

 thrown out forms a deep red, silicified covering around the green 

 interior in some cases [N.T., 150], while in others, there are small 

 cavities lined with chalcedony [N.T., 122], In the same locality 

 is a slightly schistose, pale green rock with dark green kernels 

 [N.T., 153]. This consists of pale brown opal crowded with tiny 

 plates of talc, and containing a few small crystals of chromite, 

 A somewhat similar green-veined talc-bearing rock is the sole 



