HILLEBRAND.I 
IMPORTANCE OE THOKOUU11 ANALYSES. 
17 
Si0 2 
Ti0 2 
A1 2 8 
Fe 2 3 
FeO 
MnO 
CaO 
SrO 
BaO 
MgO 
K. 2 
Na 2 
Li 2 
H 2 below 110° C. 
H 2 above 110° C. 
H 2 by ignition... 
C0 2 
P 2 5 
CI 
SO, 
Earlier 
analysis. 
44. 31 
Not est. 
17.20 
4.64 
3.73 
.10 
10.40 
Later 
analysis. 
6.57 
3.64 
4.45 
3.30 
99.11 
44. 65 
.95 
13. 87 
6.06 
2.94 
.17 
9.57 
a . 37 
.76 
5.15 
4.49 
5.67 
Trace. 
.95 
2.10 
.11 
1.50 
Trace. 
.61 
99. 92 
a Not entirely free from CaO. 
Prof. F. W. Clarke has shown that the combined percentages of 
titanic and phosphoric oxides in rocks of the earth's crust, averaged 
from hundreds of analyses, is 0.8 per cent. When the determination 
of these is neglected the error falls upon the alumina. If the latter 
is then used as a basis for calculating the feldspars, it is easy to see 
that a very large average error in the latter may result, amounting to 
several per cent of the rock. 
In order to more strongly emphasize the importance of complete- 
ness in analysis, a few facts brought out by the hundreds of rock 
analyses made in this laboratory may be cited. It has been demon- 
strated most conclusively that barium and strontium are almost never- 
failing constituents of the igneous rocks of the United States and of 
many of their derivatives. These amounts are usually below 0.1 per 
cent for each of the oxides of those metals, but higher amounts are by 
no means uncommon. Furthermore, the weight of barium is almost 
without exception in excess of that of strontium. But a still more 
important point is that the igneous rocks of the Rocky Mountain 
region, so far as examined. shoAv far higher average percentages of 
Bull. 176 2 
