272 DISCUSSION. 
other comparatively large so-called rubies stated to have been 
found in this colony, are of the same character as this specimen, 
and therefore topaz, The theory of the occurrence of these topazes, 
having this colour peculiar to burnt topaz, found in this locality, 
(because we have no reason to doubt the authenticity of this 
specimen in that respect), is, that the topazes have been altered 
to their present colour by the heat of the overlying basalt. That 
authentic rubies do exist in the neighbourhood of Mudgee is 
undoubted; in Mr. Stephen’s collection some specimens from 
that locality were determined by myself, and the results published 
in my work.' They are however, very small, being mere 
fragments. 
Passing on to the article on Zopaz, we find an analysis given 
for topaz from Emmaville. From the figures therein given, it is 
not possible to obtain the theoretical formula for topaz, as given 
by any recognised authority. We find placed by its side an 
analysis of a topaz from Tasmania for comparison. The per- 
centages there given, however, by Dana, work out almost to the 
theoretical quantity required. A perfect specimen of topaz often 
gives nearly the theoretical percentages, and when a difference 
in some of its constituents, of three or four per cent. is obtained, 
it is better that the analysis be not published. It is to be 
regretted that New South Wales topaz should by this analysis 
give results so removed from the theoretical requirements. There 
is nothing gained by publishing results or data collected, that 
do not somewhat advance our scientific knowledge, by enabling 
us to arrive ata just decision, as to the actual molecular con- 
stitution of the mineral. 
Passing on to the article on Garnet, we find that pyrope 38 
announced, and the analysis given. The Rev. J. M. Curran will 
remember, that some months ago I stated to him, that from rough 
tests I found that these stones were not pyrope. I will now show 
from the percentage constituents as given in the analysis, that 
1 “Gems and Precious Stones,” Technical Education Series, No. il, 
p. 6. 
