ABUNDANCE OF THE CHEMICAL ELEMENTS. 133 
which have been found by various observers in sea water, 
are too small to be considered. 
Comp, of salts. Comp, of ocean. 
NaCl. _ — 
. - 77-76 
O_ 
85-79 
MgCl 2 - 
. _ 10-88 
H_ 
10-67 
MgS0 4 _ 
4-74 
Cl_ 
2-07 
CaS0 4 _ 
__ 3-60 
Na___ 
1-14 
K 2 S0 4 ._.- 
_ 2-46 
Mg- 
•14 
MgBr 2 - 
_ -22 
Ca_ 
•05 
CaC0 3 _ 
_ . -34 
K__ _ 
•04 
S_ 
•09 
100-00 
Br___ 
•008 
C_ 
•002 
100-000 
Dissolved gases need not be taken into account, and no other 
constituent of the ocean can reach 0‘001 of one per cent. 
In the case of the solid crust of the earth the problem of 
ascertaining its mean composition is far less simple; for the 
crust is not an homogeneous body, but is made up, so to 
speak, of shreds and patches; of old crystalline rocks, of 
volcanic outflows, and of all manner of deposits of sedimen¬ 
tary origin. It is veined and seamed with diverse minerals, 
it encloses pockets of various materials, and upon its surface 
are quantities of organic matter and great bodies of fresh 
water. At first sight it would seem to be impossible to 
determine the average composition of such a mass, and yet, 
upon consideration, the question is not seriously complicated. 
In a crust ten miles thick a section having the superficial 
area of the United States represents only about 15 per cent, 
of the total; so that all veins, pockets, patches, organic sub¬ 
stances, etc., become insignificant in comparison with the 
whole mass, and even the lakes and rivers are neglectable 
quantities. On any attempt to compute their percentages 
they vanish into the dim recesses of the remoter decimals. 
Discarding these trivial constituents the question becomes 
one of the mean composition of the dominant rock material, 
and in that form it is comparatively simple. 
In the first place, we may assume that the volcanic and 
