IGNKOUS ROCKS OF SOUTH-WESTERN VICTORIA. 391 



lying crystalline schists. Again at Nareen, though there is granite 

 on the north, west, and east, the fertile land adjoining this 

 picturesque little township consists of decomposed volcanic rock><. 



Whenever the county of Dundas is deemed worthy of a detailed 

 geological survey (and I hope the time is not far distant) the out- 

 lines, not only of this central boss of granite, but also of the 

 surrounding area of so-called metamorphic rocks, will be materially 

 modified. 



Several varieties of granite are met with in different localities. 

 In that from Harrow both biotite and muscovite mica occur. The 

 felspar' is chiefly white orthoclase, but sparingly distributed ; there 

 is also a coh)rless plagioclastic felspar. 



The Carapook granite is similar, but the biotite crystals are 

 much larger; in both they frequently show very perfect basal 

 planes. 



The granite ui Wando Vale belongs also to the same type, but 

 is finer grained. 



The Tarrayoukyan rock is very coarse grained, the crystals of 

 orthoclase being occasionally as much as 15mm. in length. Besides 

 the biotite, which is abundant, there are also small flakes of a 

 light- colored mica. The only specimens of this rock I was able to 

 obtain are a good deal weathered. 



The Dergholm granite is porphyritic, with large crystals or 

 combinations of crystals of dark-colored quartz in a coarsely 

 crystalline felspathic matrix. Biotite and muscovite are both 

 present, but the latter only in small quantities. 



The country in which this granite is found is generally flat, and 

 the traveller only realises that he is in a granite region by the 

 numerous "• tors" met with along the road. One huge mass shown 

 to me in the bed of the Salt Creek is apparently so poised on the 

 imderlying rock as to suggest that the slightest touch would knock 

 it over. Around the "■ tors " there is only sand, the result of the 

 degradation of the granite itself. It is a friable rock, and the 

 isolated patches now seen are probably remnants only of a much 

 more extensive granitic outcrop 



As said before, the granite in Victoria Valley is of a different 

 type to that in other parts of the area. Mica appears to be entirely 

 absent, and its place is taken by a greenish mineral, which I regard 

 as amphibole. In hand specimens this appears to be scattered 

 through the rock in thin strings, or clustered together in grain-i. 

 The crystals are also irregularly defined in microscopic slides, but, 

 if small particles of the mineral are detached from the matrix and 

 crushed, the minute grains show, I think, the characteristic forms 

 of amphibole. It melts readily beft)re the blowpipe, and becomes 

 magnetic. Owing probably to its containing a rather high per- 

 centage of iron, sections must be ground very thin to render it 

 transparent — in such it shows strong pleochrism. The quartz is 

 full of inclusions. A triangular- shaped face on one of my slides 



