Chap. XII.] 
KODURITE SERIES : COMPOSITION. 
257 
on the powdered rock. The pieces on which the determination was 
made weighed 16*35 grammes. The whole of them was powdered up 
and sent for analysis to the same firm of analysts as before. The 
results of these two analyses are shown below : — 
Opalized 
Opalized 
kodurite 
kodurite 
from Kotakarra. 
from Boirani. 
A. 233 
A. 134 
Manganese protoxide 
10 '00 
. 1 '07 
Ferric oxide .... 
C-07 
. 4 -79 
Ferrous oxide .... 
0'90 
. 0 '04 
Aluruina ..... 
1150 
. 10 '59 
Lime ..... 
11 '67 
. 13-87 
Magnesia. .... 
0'14 
. 0'2f) 
Potash ..... 
O'Ol 
. 4-00 
Soda ..... 
0*18 
. 0-36 
Combined silica . . . 
... uO ou . 
Free silica .... 
. 18 OO 
no "OK 
Phosphoiic oxide . . . 
• . . . 1 oO . 
Cupric oxide . . . . , 
0 '02 
. trace 
Titanic oxide . . . . . 
0-32 
. 0-27 
Chlorine ..... 
trace 
. trace 
Combined water 
1"33 
. 1 "20 
Moisture at 100° C . 
... . 2 "30 
. 1 30 
100 '19 
100 '19 
. 0-83 
. 3-85 
54 15 
. 60T.0 
. 0-54 
As the free silica in these rocks is present in the form of opal it is 
obvious that a portion of it has probably been returned as combined 
silica. This is confirmed when it is attempted to recalculate these 
analyses into terms of the mineralogical composition of the rock. 
In the first rock, since the alkalies present are so small in amount, I 
have put them aside as impurities, although it would probably be more 
correct to convert them into corresponding amounts of felspar. In the 
Boirani rock, however, the potash present is considerable, and in this case 
