CLARKE.] 
INTRODUCTION. 
15 
If we reduce these figures to elementary form and include the 
minor constituents which are frequently found in rocks, and which in 
this laboratory are often estimated, the two averages compare as 
follows : 
Oxygen .. 
Silicon 
Aluminum 
Iron 
Calcium . . . 
Magnesium 
Sodium 
Potassium . 
Titanium . . 
Hydrogen . 
Carbon 
Phosphorus 
Manganese 
Sulphur 
Barium 
Strontium . 
Chromium. 
Nickel 
Lithium . . . 
Chlorine . . 
Fluorine.. . 
New mean. 
Old mean. 
47.02 
47. 29 
28. 06 
27.21 
8. 16 
7.81 
4.64 
5.46 
3.50 
3.77 
2.62 
2.68 
2.63 
2.36 
2. 32 
2. 40 
.41 
. 33 
.17 
.21 
.12 
.22 
.09 
.10 
.07 
.08 
.07 
.03 
.05 
.03 
.02 
.01 
.01 
.01 
.01 
.01 
.01 
.01 
100. 00 
100. 00 
As the old mean represents an attempt to measure the composition 
of the entire solid crust of the earth, and so includes an allowance for 
the carbon in the limestones, the two columns are not strictly compa 
rable. They are, however, corroborative of each other, and show that 
within reasonable limits the statistical method is applicable to the 
problem under consideration. For the arguments upon which the 
discussion is based the original paper should be consulted. The dis- 
tribution of the rarer elements has also been elaborately discussed 
by Vogt, 1 and their percentages may be regarded as small corrections 
to be applied to the table at some future time. 
By a similar statistical process I have attempted to ascertain some- 
thing with regard to the relative abundance of the more important 
rock-forming- minerals. Nearly 500 analyses of igneous rocks were 
Zeitsch. I'rakt, Geologie, 1898, pp. 225, 314, 377, 413; and 1899, pp. 10,274. 
