18 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS, [bull. 176. 
both metals than the rocks from the eastern and the more western 
portions of the United States. The following examples serve to illus- 
trate certain types of Rocky Mountain igneous rocks: Of seven rocks 
forming a Colorado series, six held from 0.13 to 0.18 per cent of BaO, 
while in the seventh the percentage was 0.43. The SrO ranged from 
0.07 to 0.13 per cent for six, and was 0.28 for that one highest in BaO. 
Of thirteen geologically related rocks from Montana, embracing basic 
as well as acid and intermediate types, the range of BaO was from 
0.19 to 0.37 per cent, with an average of 0.30 per cent. Three others 
of the same series contained 0.10 per cent or less, while the seventeenth 
carried 0.76 per cent BaO. The SrO ranged from 0.37 per cent in 
the last instance to an average of 0.06 for the other sixteen. Certain 
peculiar rocks from Wyoming carry from 0.62 to 1.25 per cent BaO, 
and from 0.02 to 0.33 per cent SrO. Surely this concentration of 
certain chemical elements in certain geographic zones has a signifi- 
cance which future geologists will be able to interpret, if those of 
to-day are not. 
Again, vanadium is an element which few chemists have ever thought 
of looking for in igneous rocks, though it has long been known to 
occur in magnetites and other iron ores. Hayes, in 1875, reported its 
occurrence in a great variety of rocks and ores. Quoting from Thorpe's 
Dictionary of Chemistry: "It is said to be diffused with titanium 
through all primitive granite rocks (Dieulaf ait), and has been found by 
Deville in bauxite, rutile, and matry other minerals, and by Bechi and 
others in the ashes of plants and in argillaceous limestones, schists, 
and sands." It is further reported to comprise, as the pentoxide, up to 
0.1 per cent of many French and Australian clays, 0.02-0.03 per 
cent of some basalts, 0.21 per cent of a coal of unknown origin, and 
0.15 per cent of one from Peru. Still later examinations in this labora- 
tory of about 100 rocks, chiefly igneous, covering the whole territory 
of the United States, show not only its general qualitative and quanti- 
tative distribution, but that it predominates in the less siliceous igneous 
rocks and is absent, or nearly so, in those high in silica. In some of 
the more basic rocks it occurs in sufficient amount to seriously affect 
the figures for the oxides of iron unless separately estimated and 
allowed for (see p. 96) — a matter of considerable importance, since the 
petrographer la}^s great stress on accuracy in their determinations. 
This same investigation has also thrown some light on the distribu- 
tion of molybdenum, which seems to be confined to the more siliceous 
rocks and to occur in quantities far below those commonly found for 
vanadium. 
Finally, had it not been the writer's practice of late years to look 
for sulphur in rocks, even when no sulphides were visible to the eye, 
its almost invariable presence in the form of sulphide, and consequent 
