204 
MR. 1ST. STORY-MASKELYNE ON THE 
Silicic acid 
I. 
. 55-389 
II. 
55-594 
Mean. 
55-491 
Oxygen ratios. 
29-28 
Magnesia . 
. 23-621 
23-036 
23-328 
9-331 
Lime . 
. 20-02 
19-942 
19-981 
5-709 
Iron oxide 
Soda . 
Lithia . . 
. 0-78 
. 0-554 
a trace 
100-364 
0-309 
[0-554] 
[a trace] 
99-435 
% 
Viewed as a magnesium and calcium silicate the percentage composition becomes — 
Silicic acid . . 56 '165 
Magnesia . . . 23' 61 2 
Lime .... 20-223 
100-000 
The formula (f Mg § Ca) Si 0 3 requires 
56-604 
23-585 
19-811 
100-000 
This does not accord with the analyses of the ordinary varieties of augite, in which 
the calcium is usually in excess of the magnesium. 
It is, however, to be observed that a small deduction of the corresponding magnesium 
silicate (enstatite) has to be made by reason of the presence of the white mineral inter- 
calated in layers along the direction parallel to the plane 0 01, and sometimes also to a 
second plane of the crystal. This mineral is doubtless the enstatite next to be described, 
and its presence would only modify the true formula of the augite by adding to the pro- 
portion of the magnesian constituent. The amount of one equivalent of enstatite to 
three of augite that this explanation would require, is more than microscopic observations 
would warrant ; and it is probable that the augite itself is richer in magnesium than is 
usual in terrestrial augites. 
The small amount of the oxide that in this augite corresponds to the ingredient of 
Osbornite that I identify with a titanoid metal, is met with in the precipitate by ammonia 
from the solution of the bases, and is included with the iron oxide in the above analyses. 
VII. Enstatite as a Constituent of the Busti Meteorite. 
Besides the augitic mineral that has just been described, there is present in this 
meteorite another silicate which is in fact its most important ingredient. The augite is 
present in greatest quantity in the nodule that contains the calcium sulphide, though it 
is met with in smaller amount in the other parts of the meteorite. But associated with 
it everywhere, and otherwise forming the mass of the stone, is the mineral I have next 
to describe. As seen in a microscopic section, it presents the appearance of a number 
of more or less fissured crystals with different degrees of transparency, sometimes quite 
clear, sometimes nearly opaque, and with a more or less symmetrical polygonal outline. 
These crystals are imbedded in a magma of fine-grained silicate, through which a sort of 
irregular mesh work of an opaque white mineral is seen to ramify. When the ingredients 
