16 
SOME PRINCIPLES AND METHODS OE ROCK ANALYSIS, [bull. 176. 
Earlier 
analysis. 
Si0 2 . 
Ti0 2 
A1A 
Cr 2 3 
Fe 2 3 
FeO. 
MnO 
CaO. 
SrO. 
54. 42 
13.37 
h . 61 
b 3. 52 
BaO 
MgO 
K 2 
Na 2 
Li 2 
H 2 below 110° 0. 
H 2 above 110° C. 
C0 2 
PA ----- 
SO, 
F 
CI 
Less O for F 
4.38 
6.37 
10.73 
1.60 
Trace. 
1.82 
99.58 
Later 
analysis, a 
53. 70 
1.92 
11. 16 
.04 
3. 10 
1.21 
.04 
3. 46 
.19 
.62 
6.44 
11.16 
. 1.67 
Trace. 
.80 
2.61 
1.75 
.06 
.44 
.03 
100. 40 
.19 
100. 21 
a A still more recent analysis of another of the series of rocks of which this is an example has shown 
that this " later analysis " is itself probably incomplete and incorrect in part— incomplete because of 
the probable presence of 0.2 per cent or more of Zr0 2 , incorrect because of the error in Al 2 3 resulting 
from having counted the ZrOo as Al 2 O y , and from the fact that titanium is not fully precipitable in 
presence of zirconium by Gooch's method (the one employed). This latter error involves both the 
Ti0 2 and the Al 2 3 . (See pp. 72-73.) 
&From the fact that repeated determinations of the iron oxides in this and related rocks from the 
same region show always a great preponderance of ferric oxide, it is not improbable that the figures 
given for the two oxides in the first analysis were accidentally transposed. 
cln the published analysis it does not appear whether this is total water or, as seems probable, only 
that remaining above 100° C. 
Another instance of similar kind is given below. Here, again, cer- 
tain differences are explainable by natural variations in the proportions 
of the constituent minerals, but it can hardly be doubted that Ti0 2 , 
BaO, SrO, P 2 5 , and S0 3 were present in both specimens in approxi- 
mately the same amounts. In the earlier analysis determinations of 
some supposed unimportant constituents were purposely omitted, or 
made only qualitatively, with results that can not be otherwise than 
fatal to a full comprehension of the mineralogical nature of the rock, 
