134 
CLARKE. 
crystalline rocks represent pretty closely the general com¬ 
position of the whole crust; for from them the sedimentary 
rocks have been formed, and the latter differ from the parent 
formations only in the carbon which they have taken up 
from the air and in the loss of saline constituents which have 
been leached out to the ocean. For this gain and loss re¬ 
spectively, approximate corrections are possible. 
In the second place, we must regard the original rock 
matter, volcanic and crystalline, as being in a large sense 
fairly homogeneous. However greatly these formations may 
vary locally, they should average pretty much alike all 
over the world when sufficiently large areas are considered. 
This assumption can be tested in the light of evidence, as 
follows: We may average together great numbers of analyses, 
grouped in various ways, and so determine whether the 
results are sensibly constant. This has been done in the 
subjoined table, minor and occasional constituents being 
temporarily omitted, to be separately considered later. 
A. The mean of 82 analyses of volcanic rocks from the 
Western Territories of the United States, published in Clar¬ 
ence King’s Survey of the Fortieth Parallel. 
B. 64 analyses of rocks from the Yellowstone Park, taken 
from the laboratory records of the U. S. Geological Survey. 
C. 54 analyses of volcanic rocks collected in Northern 
California; also from the Survey records. 
D. 39 analyses of eruptive rocks from various localities in 
the Western United States, taken from the Survey records. 
E. 80 crystalline and archsean rocks from all parts of the 
United States. Of these analyses 50 were taken from the 
Survey records, 23 from the 40th Parallel Report, and 7 from 
the report of the New Hampshire Survey, vol. 3. 
F. 75 analyses of European volcanic and crystalline rocks ; 
taken at random from five recent volumes of the Neues 
Jahrbuch. 
G. 486 miscellaneous plutonic rocks, analyzed between 
1879 and 1883, and collected by Roth in his “ Beitrage zur 
Petrographie der plutonischen Gesteine.” 
H. The mean of the foregoing 880 analyses. 
