OCCURRENCE OF PRECIOUS STONES IN N.S.W. 283 
The example No. 3 shews the opposite extreme. Here again, 
it is simply a question of being guided by one of two masters. I 
decide for Professor Heddle. 
I should like to add that oxygen-ratio (quantivalent ratio of 
modern chemistry) first introduced by Bischof in quoting mineral 
analysis, is of great utility under certain conditions. It helps in 
calculating the mineral percentages in a rock. It is of use in 
that process, dear to junior analysts, of balancing protoxides against 
Sesquioxides, and the protoxides and sesquioxides against silica. 
But it is of no value when used as Mr. Smith uses it amongst the 
protoxides themselves (which of course are isomorphous) to prove 
that a garnet is not a pyrope. The calculation of oxygen ratios 
looks imposing on paper, but instances have come within my ken, 
where this affectation of precision has afforded shelter for the 
issue of material of doubtful value. 
In making a copy of my original paper the figures for the CaO 
and the MgO were transposed by a clerical error, but it will be 
noted I am not going into the figures of the analysis in any shape 
orform. T object to the standard set up by Mr. Smith. 
Mr. Smith—“ Tf we are to adhere to the oxygen ratio for this 
class of silicates.” 
Reply —Why should we adhere to it? Prof. Heddle, Dana, 
Knap and a host of others do not adhere to it. We all adhere to 
the legitimate use of the oxygen ratio. It is not a legitimate use 
of the method to use it exclusively amongst protoxides to prove a 
certain garnet is not a pyrope. 
Mr. Smith has something to add about “recklessly ignoring — 
limits.” Here is how I learned that the stones in question were 
Pyrope. 
1, They occurred in a basic rock, and under the microscope, in 
thin slices this rock shows the radial structures called kelyphite 
shells by Rosenbusch surrounding the garnet. They show exactly 
the structure figured by Rosenbusch in his Microscopical Physio- 
-Staphy, plate xiv., fig. 4 (‘Translation by Iddings). The garnets 
