298 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
Manganese, though as widely distributed as titanium and phos- 
phorus, is usually present in such small amounts as not to allow a 
clear judgment of its magmatic relations, especially as the high 
figures often reported for it are apt to be due to analytical error. As 
a general rule, its amount is greater in the basic rocks, and certain 
considerations indicate a preference for rocks high in iron rather 
than in magnesia or lime, but the variations are not very significant. 
We have already noted above the tendency to association of barium 
and manganese. 
Nickel is preeminently at home in the basic rocks, especially in the 
peridotites and serpentines, where it replaces iron in the olivine, 
while it likewise occurs in small amounts in hornblende, biotite, and 
in pyrite and pyrrhotite. Certain rather high figures reported for it 
may be ascribed to analytical confusion with platinum derived from 
the utensils employed; but researches now in progress indicate that 
it may be present in considerable amount (up to about 0.20 per cent), 
not only in the “basic” but in the more siliceous rocks of certain 
localities where its presence has not hitherto been suspected. It is 
reasonable to suppose that it is most apt to be present in rocks which 
are relatively high in iron rather than in maganesia and lime, and 
the results of the investigation Just mentioned are in harmony with 
this supposition. 
Cobalt almost always accompanies nickel in igneous rocks, but 
always in extremely small and scarcely weighable amounts. 
The elements belonging to the next group to be discussed, those 
which are scarcely detectable in igneous rocks by the usual analytical 
methods on account of the excessively minute amounts usually 
present, need not detain us long, even though they are commercially 
among the most important. Since the analytical data are either very 
scanty, untrustworthy, or wanting altogether, and their presence is 
revealed to us mostly through secondary processes of concentration 
in veins, placers, and other ore deposits, we are not yet in a position 
to generalize with confidence as to the magmatic relations of most 
of them. 
Furthermore, having but slight affinity for silica, and thus (with 
few exceptions) seldom forming silicates or entering as minor con- 
stituents into the silicate minerals of other elements, we are deprived 
to a very great extent of this kind of evidence. 
Copper is not infrequently reported in analyses of igneous rocks, 
but, as pointed out by Hillebrand, its apparent presence may often 
be attributed to contamination during the course of analysis, or as 
may be suggested here, to confusion with platinum likewise due to 
contamination, as was suggested in the case of nickel. But notwith- 
standing these sources of error, copper seems to be widely distributed 
among igneous rocks, though in very small amounts. There seems 
