The larger number of elements play so small a part in the constitution
of the earth that they may be neglected by the geologist. The following
list includes the elements of which ninety-nine per cent of the earth’s
crust, as known to us, is composed, with their relative proportions, as
indicated by Clarke’s laborious analyses of a very large number of
typical rocks:
=========+========+==============
ELEMENT |CHEMICAL|PERCENTAGE OF
| SYMBOL |EARTH’S CRUST
| |WHICH IT FORMS
---------+--------+--------------
Oxygen | O | 47.02
Silicon | Si | 28.06
Aluminum | Al | 8.16
Iron | Fe | 4.64
Calcium | Ca | 3.50
Magnesium| Mg | 2.62
Sodium | Na | 2.63
Potassium| K | 2.32
Hydrogen | H | 0.17
Carbon | C | 0.12
| | -----
| | 99.24
---------+--------+--------------
The ten elements given above form
99.24 of the earth’s solid crust.