218 REV. J. MILNE CURRAN. 



in his paper on the microscopic structure of crystals.* Some of 

 these cavities can easily be seen with a power of three hundred 

 diameters. As in other granites, I notice that the smallest cavities 

 contain the most active bubbles. Many of the broad patches of 

 quartz break up into smaller patches under crossed nicols. An 

 examination of the slides shows that the quartz was the last 

 mineral to solidify. The rock contains both orthoclase and plagio- 

 clase, but the latter felspar being comparatively speaking, rare. 

 There is a good deal of felspar exhibiting in polarized light a 

 cross-banded structure, the bands crossing each other at an angle 

 of 90°. Slice 72 contains some very characteristic hornblendes 

 around which the quartz and felspar are seen to be perfectly 

 moulded. Biotites on this same slide seem more twisted and 

 broken than in any Australian granites I have met. Micro- 

 photographs of some of these interesting examples are exhibited 

 with this paper. These biotites contain inclusions of a mineral 

 very much resembling magnetite. Magnetite occurs also as an 

 inclusion in the hornblendes. 



Slice 73. — Sphserulitic Quartz Porphyry from Carcoar, New 

 South Wales. This is a rock intimately connected with gabbro 

 and other basic rocks near Carcoar. It occurs in dykes and veins 

 cutting through the intrusive basic rocks and sometimes through 

 the Silurian slates of the district. In hand-specimens, the rock 

 is of a very fine grain and of a cream yellow colour. Quartz is 

 the only individualised mineral visible to the unaided eye. Quartz 

 however, is not very plentiful, four or five patches being the most 

 that I have noticed on any slide. The bulk of the rock is remark- 

 ably free from inclusions, if we except some lines and stains of 

 ferrite in the slices which I have prepared. Under the microscope 

 in common light, the felsitic character of the rock is at once 

 apparent. The radial structure of the sphserulites can also be 

 made out by a nice adjustment of the sub-stage illumination. It 

 is in polarized light, however, with crossed nicols, that the 

 beautiful and characteristic structure of the felsitic base is seen. 



* Quart. Journ. Geol. Soc. London, Vol. xiv., p. 453. 



