Yol. 50.] GEOLOGY OF BATHUEST (NEW SOUTH WALES). Ill 



traverses the central mass of granite is probably connected with the 

 second intrusion. 



In the ]S"ew England district, Northern New South Wales, 

 Prof. T. W. E. David, E.G.S., recognizes granitic rocks of at least 

 two ages. 1 In Victoria most of the typical granites are classed 

 as newer than the Silurian, but older than the Upper Palaeozoic 

 strata. 2 



A fairly typical specimen of the biotite-granite, from the Water- 

 works, Bathurst, gave on analysis 68*5 per cent, of silica; its specific 

 gravity was 2*75 to 2 # 79. Granite close to the junction with schist 

 yielded 73-5 per cent, of silica. Specific gravity 2-59 to 2-62. 



3. The Silurian Rocks. 



Very good exposures of the junction of the granite with the 

 overlying rocks occur at many localities around Bathurst, and one 

 is at once struck by the similarity of the contact-rocks when 

 examined at places as much as 20 miles apart. The metamorphic 

 rocks at the contact differ to some extent among themselves, as to 

 fineness of grain and in other ways, but they are nearly all of the 

 same type — namely, a kind of hornblende-schist, although they can 

 hardly be called typical schists. Most of them are tolerably coarse- 

 grained, but some are so fine that they appear like quartzite or 

 fine-grained felstone. Under the microscope they are seen to consist 

 largely of quartz, with a good deal of a green mineral, strongly 

 dichroic, but not usually occurring as distinct crystals or showing 

 cleavage-lines. It is probably altered hornblende, the rock having 

 evidently undergone much change from its original condition. 

 Perhaps the best name for the contact-rock is hornfels, as suggested 

 by Mr. Curran. 



An average specimen of this rock, from the Wimburndale Creek, 

 near Peel, gave 66 per cent, of silica ; granite from the same 

 locality yielded 73'5 per cent. The specific gravity of the hornfels 

 varies from 2*75 to 3. A collection of the contact-rocks was shown 

 by the writer to Mr. A. W. Howitt, F.G.S., who remarked that 

 he could match them all from Gippsiand, Victoria. 



In all cases the junction is sharp and well defined, there being 

 no instance known to the writer in which there is any indication 

 of a gradual passage from the granite to the hornfels, such as 

 would suggest that the granite had resulted from the extreme 

 metamorphism of the overlying rocks. There is often a creek 

 running roughly parallel to the junction, so that the line of contact 

 may be followed for a considerable distance at several localities. 

 The line is an irregular one and winds about in a curious manner : 

 the granite often sending small veins into the metamorphic rock, 

 so that there can be no possibility of a faulted junction. The 



1 ' The Geology of the Vegetable Creek Tin-Mining Field,' by T. W. Edge- 

 worth David, F.G.S., Department of Mines. N.S.W., 1887. 



2 ' Victoria — Geology and Physical Geography,' by Reginald A. F. Murray, 

 Melbourne, 1887, p. 24. 



