376 PROCEEDINGS OF SECTION C. 
The obscuration angles measured in these slices are tabulated 
below, being the mean of a number of nearly agreeing readings. 
No. P M | + to Pand M 
I Ab By 4p + 12° 30’ + 10° 0’ 
IT + 3° 3! + 12° 19’ ee ae Gy 
Seen by convergent polarised light, there is upon P the appear- 
ance of a bar indicating the exit of a bisectrix beyond the field 
of view on the left. Upon M there is the exit of the positive 
bisectrix, and upon each of the planes 1 and T there is the well 
marked exit of an optic axis approaching to a normal position to 
those planes respectively. 
These observations, which agree nearly in both samples, indicate 
a soda lime felspar of the oligoclase group. But the obscuration 
angles observed upon P appear to be somewhat high when com- 
pared with the data in a table prepared by Schuster.* An obscura- 
tion of 3° upon P and of 12° 30’ upon M may, however, be taken 
to indicate an oligoclase somewhat higher than the composition 
Ab. 6 to An. 1. 
In order to have a control over these results, I obtained 
a quantitative analysis of the remainder of each sample, which Mr. 
Francis E. A. Stone, the Analyst to the Victorian Department of 
Mines, kindly made for me. 
The two quantitative analyses are given below. Of the two, a 
preliminary examination showed that No. Il was the more reliable, 
and I therefore made use of it, with the following results :— 
I II Remarks. 
SiON ceniensces 62°98 62:22 (1) Fe,0,-tr. 
INGO G6 noaooapoc 21°88 (1) 22°42 (1) 
CAOR Cite 2°78 3°34 
INGO: cmoceene tr tr. 
INe)5(O)s noodononane 5°00 6:14 
Ke OM eccni 1:90 2°30 
Unestimated 
loss: Nose 5°46 3°58 
100:00 100:00 
As to these analyses, Mr. Stone appended a note that in all 
probability they were rather low, as the laboratory did not possess 
the proper crucible for doing the fusions by Dr. Lawrence Smith’s 
method. I calculated out the analysis into equivalent proportions, 
and found, in tabulating the results according to the formule for 
* Hintze, Handbuch der Mineralogie, 1897, p. 1439. 
