ELEMENTS IN IGNEOUS ROCKS—WASHINGTON. 285 
data given here approximate closely to the average composition of 
the earth’s accessible igneous rocks. 
In column III are given the results of a more complete estimate by 
Clarke, which includes the minor constituents frequently present in 
igneous rocks, but which are only determined in the more complete 
analyses, as those made by the chemists of the United States Geo- 
logical Survey. It will be seen that the data are in agreement with 
the general composition of the most common rock-forming minerals, 
their constituents, silica, alumina, ferric and ferrous oxides, magnesia, 
lime, soda, potash, and water, making up 97.9 per cent. 
The estimated amount of carbon dioxide is undoubtedly too high, 
and is due to the number of analyses of altered rocks which were 
included in the estimates. 
We may examine the matter further and, resolving the oxides 
into their elementary components, ascertain the average amounts of 
the elements in the igneous crust of the earth. This problem has 
been studied by Clarke in the papers already cited, and by Vogt? in 
Norway. The results of Clarke’s latest calculations are given in 
column IV of Table I, the figures including those for the minor con- 
stituents of column III, just noticed. In an earlier computation 
Clarke introduced estimates of the elements which make up the air, 
the water of the oceans, and such nonigneous rocks as limestone and 
coal. But the introduction of these into the calculation does not ma- 
terially alter the final results from those given here, in which they are 
omitted, since these bodies are of relatively very slight quantitative 
importance compared with the whole mass of known rocks, however 
large they may loom to our eyes. Ore bodies also are quite negligible 
in this connection. 
These data show that oxygen composes almost one-half, silicon 
more than one-quarter, and aluminum about one-twelfth of the 
earth’s crust (the three together amounting to 83.3 per cent), while 
iron, calcium, sodium, magnesium, potassium, and titanium follow 
after in the order named in decreasingly small amounts. Thus, 
only nine elements together constitute 99 per cent of the igneous 
crust. This is certainly a very remarkable fact, and one doubtless of 
great significance for the proper understanding of the true constitu- 
tion of our globe, could we but interpret it aright, as some day we 
may hope to do. 
The relatively high position occupied by titanium, ninth on the list 
in the order of abundance, is also a striking feature, as this element 
is commonly supposed to be rare. The establishment of this fact is 
largely due to the accuracy and completeness of the rock analyses 
made by the chemists of the United States Geological Survey, and 
«J, H. LL. Vogt, Zeitschrift fiir praktische Geologie, pp. 225-2388, 314-325 (July 
and September, 1898). 
