THE RELATIVE ABUNDANCE OF THE CHEMICAL 
ELEMENTS. 
BY 
Frank Wiggles worth Clarke. 
[Read before the Society, October 26, 1889.] 
In the crust of the earth, with its liquid and gaseous en¬ 
velopes, about seventy chemical elements are at present 
recognized. Others, as yet unknown, are indicated by gaps 
in the periodic system and will probably be discovered in 
the future. Some of the elements are quite plentiful, some 
are exceedingly rare, and in any thorough discussion of 
their nature and relations this comparative abundance or 
scarcity should be taken into account. Even though the full 
meaning of the facts may not be discoverable for many years 
to come, it is worth while to put them into something like 
systematic order. 
In its larger aspects the general problem is at present un- 
solvable, for the reason that we know nothing of the earth’s 
interior. Its surface only is within our certain reach, and 
from the composition of that we must draw nearly all our 
conclusions. For that which lies below the crust we must 
be content with inferences based upon the scantiest of data. 
Of the crust itself the average composition is easily comput¬ 
able, and the calculation gives results which are in some 
respects surprising. 
In order to have a definite mass of matter under consid¬ 
eration, we may assume for the earth’s known crust a thick¬ 
ness of ten miles below sea-level. The volume of that crust, 
including the mean elevation of the continents above the 
sea, is 1,935,000,000 cubic miles. Of this amount 302,000,000 
14—Bull. Phil. Soc., Wash., Vol. 11. 
(131) 
