116 ME. W. J. CLT7NIES EOSS ON THE [May 1 894, 



situated. The Coal Measures appear to belong to the tipper series 

 and are probably of Permian age, but beneath them is a series 

 of sandstones and shales, considered to belong to the Lower Coal 

 Measures, or Upper Marine series, of New South Wales, and to be 

 of Middle or tipper Carboniferous age. These were found by 

 Mr. Wilkinson to be quite unconformable to the Devonian beds. 

 The exact limits of the Carboniferous rocks are scarcely known ; 

 but they do not appear to approach Bathurst, and it is doubtful 

 whether they, or any Mesozoic beds, ever existed in the district. 



6. The Later Tertiary Rocks. 



In this neighbourhood there are several distinct beds of gravel. 

 The highest, and no doubt the oldest, is situated west of the town, 

 near the top of the Bald Hills. It is composed of well-rounded 

 pebbles, made up almost entirely of quartz, which have evidently 

 been rolled a considerable distance, since none of them are large ; 

 and it carries a little gold, but is not rich. 



The basalt which caps the hills is about 200 feet thick. It is 

 a moderately coarse-grained rock, containing numerous crystals of 

 augite and olivine in a matrix which, under the microscope, is seen 

 to be mainly made up of lath-shaped crystals of plagioclase-felspar. 

 Microscopic sections present a remarkably fresh appearance, and 

 sometimes show flow-structure very well. Some specimens show 

 numerous white spots of calcite. When freshly broken the rock is 

 of a bluish-black colour, and it is often columnar, the columns being 

 about 12 to 18 inches in diameter, rather irregular in shape, from 

 four- to seven-sided, five sides being perhaps the most usual. The 

 columns show the usual transverse jointing, with occasionally the 

 ball-and-socket arrangement at the ends, but this is not common. 

 The rock makes first-rate road-metal. Mr. Curran 1 quotes an 

 analysis by Mr. Mingaye, of the Mines Department, giving : — 

 Silica 44-67 per cent., alumina 21*38, lime 10*24, magnesia 9 - 58, 

 ferrous and ferric oxides 8*81. The writers determination of the 

 silica agrees fairly well with this. The specific gravity of several 

 specimens gave a mean of 3 - 2. 



Mr. Wilkinson was of opinion that the basalt came from Swatch- 

 field, about 40 miles S.E. of Bathurst, near the head of the Fish 

 and Campbell rivers. A specimen of basalt from Oberon, which 

 is in that direction, is finer-grained than the Bathurst rock, but 

 presents similar characters under the microscope ; this confirms 

 Mr. Wilkinson's opinion. There are, however, some indications that 

 the basalt may have come from a different direction. The flow can 

 be followed along the top of the Bald Hills for about 4 miles, to near 

 the village of Perth, but there ceases abruptly, and there is no 

 basalt known to the writer in the direction of Swatchfield for at 

 least 20 miles. The trend of the flow is also rather away from 

 that direction. At Blayney, 20 miles S.W., and Orange, 35 miles 



1 ' Geology and Petrography of Bathurst,' Proc. Linn. Soc. N.S.W., ser 2, 

 vol. vi. (1891) p. 227 ; sep. cops. p. 57. 



