THE DISTRIBUTION OF BARIUM. 189 
Assuming that the value of o.n for BaO in the igneous rocks of the United 
States is correct, it must be noted that the data include many analyses of rocks from 
regions where this constituent is prominent, and to judge from the meager indica- 
tions at hand for other parts of the globe, it would seem that the average for the 
earth as a whole is considerably lower than this. Exactly how much less it is im- 
possible to say, but it is probable that the average percentage of barium in the igneous 
rocks of the globe may be put at about 0.05, equivalent to about 0.06 of BaO. While 
this figure is based on admittedly insufficient data, it is probably not far from truth, 
and may be accepted provisionally for the present. For Europe, at least, it is 
undoubtedly less than for the United States. 
Examining analyses in which BaO has been determined, those of the United 
States, New South Wales, British Guiana, and the Roman Region, it is found 
that this constituent tends to increase as silica decreases, though this is not marked, 
and seems to be subordinate to other relations. These are that rocks high in BaO 
are likewise apt to be high in K 2 O, especially if considerable CaO is also present. 
On the other hand, rocks high in Na 2 O, and those which are docalcic or percalcic 
(that is with very subordinate amounts of the alkalis) show very small amounts of 
BaO as a rule. 
All the specific data can not, of course, be cited here, but the following illustra- 
tions may be given. In the rocks of the Leucite Hills in Wyoming, which are the 
richest in potash as well as in barium so far known, with an average percentage of 
10.53 for K 2 O, BaO is 0.80, in the Central Montana Region the average for K 2 O is 
4.75 and that of BaO is 0.33, while in the Roman Region the figures are respectively 
7.93 and 0.16. The average percentage of K 2 O in central Montana may not seem 
.very high, but it is very considerably above that for the igneous rocks of the United 
States, 2.93,* or for the earth, 3-i6.f That for the Roman Region is much above 
this, and relatively high potash is also shown by the frequent occurrence of leucite 
rocks in both regions. While the figure for BaO in the Roman Region may seem 
low, it is above the average one as stated above, and certainly above that for Euro- 
pean rocks so far as the data at hand allow us to judge. 
Examples of the converse of the above among the rocks of the United States 
are so numerous that it is needless to cite instances. An examination of the analy- 
ses recorded in the bulletins mentioned above will disclose the frequency of figures 
for BaO varying from o.io to none in the rocks of comagmatic regions where leu- 
citic rocks do not occur, and where Na 2 O is the dominant alkali or where salic lime 
dominates over the alkalis. Similarly in British Guiana the analyses of Professor 
Harrison show an average percentage for K 2 O of 2.47, while that of BaO is about 
0.02, and this latter constituent is reported as absent in half the analyses. 
The igneous rocks of New South Wales furnish somewhat different results. 
Here 46 excellent analyses published between 1902 and 1905 in the records of the 
* Clarke, Bull. U. S. Geol. Surv. No. 228, 1904, p. 19. 
t Washington, Prof. Paper U. S. Geol. Surv. No. 14, 1903, p. 107. 
