Yol. 50.] GEOLOGY OF BATHUESX (NEW SOUTH WALES). 117 



west, there is plenty of basalt, but this is of an entirely different cha- 

 racter from the Bathurst rock, so that the latter is not likely to have 

 come from either place. At a hill called Fitzgerald's Mount, about 

 14 miles west, the writer has found a basalt much resembling 

 Bathurst basalt in microscopic characters ; but further examination 

 is necessary before one can speak with confidence on the subject of 

 its identity or otherwise. 



As to the age of the drift under the basalt little can be said. 

 Diligent search has so far failed to reveal a single fossil, except 

 some pieces of silicified wood, in that or any other Bathurst drift. 

 It is about 400 feet above the level of the Macquarie Biver, and 

 at the time it was deposited there was probably high ground 

 over much of the present Bathurst Plains, so that it must have 

 taken a long time to denude away so great a thickness of rock. 

 The granite which underlies the drift is, as already mentioned, 

 much decayed to a considerable depth from the surface, and this 

 decayed granite is sometimes worn away very quickly, deep creeks 

 being formed in the course of a few years. 



It is, indeed, a characteristic of the country around Bathurst to 

 find creeks from 10 to 20 feet deep, with vertical sides, and termi- 

 nating abruptly at the head of the channel. These sometimes form 

 a miniature river-system : there being a central channel with 

 numerous tributaries, all running in canons on a small scale. 



The creeks are usually dry, except after heavy rain ; but if in 

 the past the rainfall was much greater than it is now, from 20 

 to 30 inches a year, the work of denudation may have gone on 

 very rapidly. 



The freshness of the basalt does not indicate a great age, and 

 probably the oldest gravels are not older than the Pliocene period. 

 The gravels next in age to that on the Bald Hills are at a much 

 lower level, but of similar character, being formed of small quartz- 

 pebbles, with beds of sand, and showing much false bedding. The 

 later gravels, however, which form terraces roughly parallel to the 

 Macquarie, are of different character, being much coarser and con- 

 taining large pebbles, mainly of Devonian grits and felstones; 

 they are very similar to the present river-gravel. 



Y. Sttmmaey. 



The probable geological history of Bathurst, so far as at present 

 known, may be thus briefly summarized: — The oldest sedimentary 

 rocks of the district are Silurian. There was evidently an upheaval 

 some time after the close of the Silurian period and before the 

 Carboniferous ; there may have been more than one such move- 

 ment. The Silurian strata may possibly have been folded before the 

 granite was erupted, as it is suggested those of Yictoria were ; but 

 this is uncertain. In any case, the granite produced a zone of con- 

 tact-metamorphism, while almost the whole of the Silurians may 

 be considered to be examples of ' regional metamorphism ' ; but 

 the agents producing changes in the rocks were most active south 



