228 REV. J. MILNE CUERAN. 



of quartz are easily found on examining the specimens. On 

 separating]these quartzes from the rock, their surfaces are found to 

 have a dull ground-glass appearance. On mounting these granules 

 in balsam, *they become transparent, and in this way I have dis- 

 covered that they contain fluid inclusions with moving gas bubbles. 

 A very interesting structure is discovered on submitting the slice 

 to a microscopic examination. The porphyritic felspars are seen 

 to be surrounded by a pseudo-sphserulitic fringe of radiating 

 microlites. When two felspars occur close together, on the slice, 

 I notice that a fringe surrounds the two crystals in one waved 

 line, which conforms to the outlines of the crystals. This is the 

 only Australian rock in which I have es^er observed this fringe 

 structure. I have very little doubt that these fringes are 

 secondary products, intimately connected with the decomposition 

 of the felspars.* In general microscopic characters, the rock is 

 very much altered — the felspars are kaolinized and the clear 

 patches, seen through the slice, are evidently devitrified matter, 

 that once formed a glassy base. Pending a more detailed 

 examination of these interesting slices, I think I may include 

 this rock amongst the felspar porphyries. 



Slice 162. — Felspar Porphyry from Mount Foster, Lower Mac- 

 quarie River, New South Wales. A short distance from Mount 

 Harris, there is another isolated, conical hill rising in a similar 

 manner from the plains. In macroscopic characters it seems 

 to differ from the Mount Harris rock ; but a microscopic examin- 

 ation proves the two to be identical. The decomposing felspars 

 give the rock a reddish tinge which does not show in the Mount 

 Harris specimens. The pseudo-sphserulitic fringes and the peculiar 

 corroded quartzes are also present. From a study of these rocks 

 in the field I am of opinion that in Mount Harris and Mount 

 Foster we have some representatives of the most ancient eruptive 

 masses in New South Wales. 



* Somewhat similar fringes hav,e been described by Prof. Judd in a 

 paper on "The Growth of Crystals in Igneous Bocks after their Consoli-f 

 dation " — Quart. Journ. Geol. Soc, Vol. xlv„ p. 183. 



