Vol. 50.] GEOLOGY OF BATHURST (NEW SOUTH WALES). 107 



channel, and in time of flood is a fine stream. For the greater 

 part of the year, however, it only fills a small part of its bed. The 

 hills to the east are drained mainly by the Wimburiidale Creek, 

 which has a course of considerable length, and enters the Macquarie 

 a long way below Bathurst. Near the centre of the Plains, and 

 about 2 miles south-west of the city, are the Bald Hills, about 

 60O feet high, capped by a mass of basalt, 200 feet tbick ; beneath 

 this is a layer of drift-gravel, which in places has been cemented 

 into a compact conglomerate. There are also several terraces of 

 gravel, capping the lower hills and running roughly parallel to 

 the course of the river. 



The Bathurst Plains form an extensive granite area, estimated at 

 450 square miles, while the hills, which rise at an average distance 

 of 10 miles from the city, are formed of metamorphic rocks. The 

 granite can be followed on the surface, however, for a much greater 

 distance around the valley of the Fish Biver and its tributaries. 

 The metamorphic rocks consist partly of highly altered rocks, such 

 as crystalline marbles, mica- and hornblende-schists ; partly of less 

 altered varieties, such as massive slates and silky schists, with, in 

 places, beds of limestone containing many fossils. They are probably 

 all Silurian, but east of Bathurst they are backed by a bold escarp- 

 ment of Devonian rocks, consisting mainly of quartzites and sand- 

 stones. These attain a height of 4000 feet above sea-level, but 

 appear to be absent from the north, south, and west of Bathurst. 

 Mr. Curran states that the Devonian is overlain by Carboniferous 

 beds, but no rocks of that age are known to the writer as occurring 

 around Bathurst. (See Map and Section, pp. 108, 109.) 



IV. Detailed Geology of the District. 

 1. The Central Area. 



The granite over the greater part of the country is much decayed 

 near the surface, owing to the decomposition of its felspar. It 

 often appears compact enough where exposed on the banks of creeks 

 and in road-cuttings, but crumbles down at once when touched with 

 the hammer. In places, however, the granite is hard and compact, 

 and consists of light-grey felspar, quartz, black mica, and very often 

 hornblende, with sphene and apatite as accessory minerals. It is 

 mostly rather coarse-grained, with, in some localities, large crystals 

 of pale pink orthoclase, porphyritically developed. 



At the Waterworks, Bathurst, small veins of calcite and prehnite 

 occur, developed along the joint-planes of the solid granite. When 

 examined microscopically, most sections show a good deal of plagio- 

 clastic felspar, probably oligoclase, so that the rock might be called 

 a granitite, and affinities are suggested with the quartz- mica-diorites 

 of Gippsland, Victoria, described by Mr. Howitt. Some of the 

 large crystal* of orthoclase show interesting instances of zones of 

 growth around the outlines of the crystals, and also a cross-hatched 

 structure suggestive of microcline. 



i2 



