70 
PETROGRAPHICAL OBSERVATIONS UPON SOME 
SOUTH AUSTRALIAN ROCKS. 
By J. Cottetr Mouupen, Associate Royal School Mines, London. 
Communicated by J. East, F.G.S. 
[Read May 7, 1895.] 
Through the kindness of Mr. J. J. Hast, F.G.S., Registrar of 
the School of Mines and Industries, Adelaide, I have been 
enabled to examine a small series of rocks, chiefly South Aus- 
tralian, from the collection of that Institution, and the following 
observations on them may prove of interest. 
In each case, thin sections for examination under the micro- 
scope were cut, and the component minerals of the rock, its 
nature, structure, and texture were examined. 
The sections number 20 in all, and some possess many points 
of interest. 
The contributions to the Petrography of South Australia have, 
in the past, been very meagre—the harvest indeed is rich but 
the reapers few—and the few notes herewith appended will, I 
hope, merely serve to point out the great desirability of such 
work being actively pushed forward in the near future. 
I wish it to be quite understood at the outset that these rocks 
have been named on petrographical grounds, combined with a 
microscopic examination of the hand specimens. I have, un- 
fortunately, at present, no opportunity of studying these 
examples in the field, and knowing what a terrible stumbling- 
block in geology the nomenclature of rocks is, one may easily 
conceive that some of the names may have to be slightly modi- 
fied after an examination of the rocks im situ. Even under such 
circumstances the names to be applied to them is greatly a matter 
of individual opinion. 
The localities of the rocks are mostly well known and authen- 
ticated—some, indeed, were personally collected by Mr. East— 
and these circumstances render it the more desirable that reliable 
information should be forthcoming concerning them. In some 
cases the specific gravity of the rocks was taken by means of a 
Walker’s balance. 
I. OutvenE Basatt, Mount Eden, Auckland, N.Z. 
The rock consists of plagioclase, olivene, and magnetite in 
grains, with a fair amount of augite. The olivene is fresh, gives 
the usual splendid polarisation-colors, and has the usual irregular 
