THE DISTRIBUTION OF BARIUM. 
In the comparison of the Roman and Central Montana Regions it was noted 
that the rocks of both regions are characterized by the presence of large amounts 
of barium, large, that is, for this constituent, the amount of which in igneous rocks 
is very seldom over i per cent and usually less than one-tenth of this. It will be 
appropriate, therefore, in this connection to discuss briefly the distribution of barium 
among igneous rocks. 
Hillebrand* and Vogtf have called attention to its widespread occurrence, and 
the former has pointed outj the local variation of the igneous rocks of the United 
States in regard to this constituent, in that those "of the Rocky Mountain region 
show far higher average percentages than the rocks from the eastern and more 
western portions." It will be of interest to examine its distribution from another 
point of view, not so much that of the locality as in relation to the other chemical 
characters of the magmas or comagmatic regions. 
Our data for such a discussion are unfortunately somewhat scanty. In the 
igneous rocks of the United States BaO has been determined very frequently by 
the chemists of the Geological Survey, especially in the more recent analyses, where 
it is invariably looked for. It is also regularly determined by the chemists of the 
Geological Survey of New South Wales, and has been determined frequently in 
the rocks of British Guiana by Professor J. B. Harrison. For the igneous rocks 
of Europe, as well as of Asia and Africa, determinations of BaO are almost non- 
existent, those presented in this paper being about the only ones to be found. In- 
deed BaO, as well as most of the other minor constituents, have been usually neg- 
lected in rock analysis. Outside of the main constituents, TiO a , P a O s and MnO 
are the only minor ones to which attention is commonly paid. 
The average percentage of barium in the earth's crust was first estimated by 
Clarke in 1891, the figure, 0.03 per cent, being based only on analyses of rocks of 
the United States. This was later and successively! raised to 0.04, 0.05, and 0.089,- 
these figures applying only to the igneous rocks of the United States. The reason 
for the great difference between the earlier estimates and the latest is the difference 
in method of computing the means. 11 In the earlier estimates all the analyses were 
averaged as if each was complete, while in the last the determinations for each con- 
stituent were averaged separately. As BaO was not determined in many of the 
analyses, this would lead to low figures by the former method. 
* W. F. Hillebrand, Jour. Am. Cliem. Soc., XVI, 1894, p. 81. 
t J. H. L. Vogt, Zeits. prakt. Geol., 1898, p. 231. 
% W. F. Hillebrand, Bull. U. S. Geol. Surv. No. 148, 1897, p. 19. 
F. W. Clarke, Bull. U. S. Geol. Surv. No. 78, 1891, p. 39. 
|| Clarke, Bulls. U. S. Geol. Surv. No. 148, 1897. p. 13; No. 168, 1900, p. is; No. 228, 1004, p.ip. 
1 Clarke. Bull. U. S. Geol. Surv. No. 228, 1904, p. 16. 
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