Hillebband.] STATEMENT OF ANALYSES, 21 
terrestrial origin — the more or less stony meteorites — will not be con- 
sidered. An analysis of that kind should never be intrusted to the 
novice, but only to the chemist who has a knowledge of the composi- 
tion and properties of the peculiar mineral constituents of those bodies 
and a judgment lit to cope with the oftentimes difficult problems pre- 
sented by them. 
Thorium, cerium, and other rare earths are seldom encountered in 
quantities sufficient to warrant the expenditure of the time necessary 
for their isolation. A search for them qualitatively, even, is at present 
rarely justifiable unless there is microscopic or other evidence of the 
presence of minerals likely to contain them. Tantalum, columbium, 
boron, and glucinum have never been certainly met with in the writer's 
experience, and yet they must be present in certain rocks, and doubt- 
less traces have been overlooked at times. There is no reason to sup- 
pose that other elements may not be found by careful search, possibly 
all in the known category, and, indeed, Sandberger's researches have 
shown to what an extent this is true of a large number of those ele- 
ments contributing to the filling of metalliferous veins. But those in 
the above list may usually be estimated with ease in weights of from 
one-half to 2 grams. 
If the point be raised that many of the published analyses emanating 
from the Survey laboratories, even the earlier ones of the writer, are 
not in accord with the advocacy of completeness contained in the fore- 
going pages, it may be remarked that these ideas have been to a con- 
siderable degree evolved during a personal experience of twenty years 
in this line of work, and that frequently the exigencies were such as to 
compel restriction in the examination. Where the latter has been the 
case subsequent developments have in some cases shown it to be bad 
policy in every respect. It is better, both for the geologist and the 
chemist, to turn out a limited amount of thorough work than a great 
deal of what may prove to be of more than doubtful utility in the end. 
III. STATEMENT OF ANALYSES. 
Until recentl} T it has been the practice in this laboratory to tabulate 
the constituents of a rock somewhat in the order of their determina- 
tion, beginning with Si0 2 as the chief constituent and grouping 
together all chemically related oxides, as shown, for instance, on 
pages 16 and 17. 
From a strictly scientific point of view a chemical classification 
founded on a separation into basic and acidic atoms or radicals would 
be more satisfactory, but until we Learn to find out what silicic radicals 
are present and in what relative amounts, also how much free silica 
there may be, it is useless to think of employing the arrangement so 
valuable in stating water analyses. 
