MICROSCOPIC STRUCTURE OF SOME AUSTRALIAN ROCKS. 219 



The sphserulites too, are seen to advantage, showing the arms of 

 a black cross very distinctly. The sphserulitic quartz-porphyry, 

 described and figured by Mr. W. Anderson* bears a striking resem- 

 blance to this rock. Fig. 2, on plate II. a, of Mr. Anderson's, 

 paper agrees with the characters of part of Slice 73. 



Slices 75 and 76 are quartz felsites from Sunny Corner. These 

 rocks have been so well described by Mr. Anderson in the paper 

 just referred to, that there is no object to be gained in going over 

 the same ground again. My slices show the corroded quartzes 

 remarkably well, as also the flow structure referred to by Mr^ 

 Anderson. There are no sphserulites present in my slices. 



Slice 77. — Quartz-felsite from ten miles south of Dubbo, New 

 South Wales. This rock is found intrusive in granite. Under 

 the microscope it shows a micro-felsitic base in which there remain 

 obscure traces of triclinic felspars. The quartzes occur in water- 

 clear grains with corroded edges. In hard specimens, wavy lines 

 of flow can be seen spreading round the porphyritic quartz crystals.. 

 This rock might be called a rhyolite. 



Slice 78 is another sample of the same rock. 



Slice 79. — Quartz-felsite from Peak Hill, New South Wales. 

 This specimen is taken from the top of Peak Hill, near the 

 locality known as Maguire's Lease. In hand specimens it appears 

 as a grey rock of a rather flinty character. Under the microscope 

 it is found to contain a surprising quantity of iron pyrites. In 

 ordinary light the microscope reveals a brecciated structure. Frag- 

 mentary pieces are seen set in a felsitic ground-mass ; boundaries 

 between the base and these inclusions are very distinct. But a 

 notable change is observed when the rock is examined between 

 crossed nicols — the boundaries between the fragmentary rocks 

 and the base disappear, and the whole field represents a uniform 

 felsitic structure. 



* Petrographical Notes on the Eruptive Rocks connected with the Silver- 

 bearing Lodes at Sunny Corner, Mitchell, near Bathurst, with Plates II. 

 and Il.a, by W. Anderson, Geological Surveyor — Eec. Geol. Survey N. S.. 

 Wales, Vol. i., Part i., 1889, p. 16. 



