52 
THE GEOLOGIST. 
iuciease this number to seventeen ; the five additional elements, 
although not occurring abundantly compared with the others, being 
yet essential and characteristic chemical constituents of many rock- 
forming minerals. The following is a list of these seventeen elements, 
■with their chemical symbols affixed : — 
1. 
Oxygen 
. 0. 
c. 
Fluorine . 
Fl. 
11. 
Magnesium 
. Mg. 
2. 
Hydrogen . 
. H. 
7. 
Silicon . . 
Si. 
12. 
Barium . 
Ba. 
3. 
Carbon . 
. C. 
8. 
Boron 
B. 
13. 
Potassium. 
K. 
4. 
Sulphur 
. S. 
9. 
Aluminium , 
Al. 
14. 
Sodium . 
Na. 
5. 
Chlorine . 
. CI. 
10. 
Calcium . 
Ca. 
15. 
Lithium . 
Li. 
IC. Iron .... Fe. | 17. Manganese . . Mn. 
XIIL These seventeen elements, combined in the most various 
proportions, make up the entire mass of rocks, excepting some rare 
and exceptionable species, — and also excepting, of course, their con- 
taining veins. As fifteen of them, however, always occur in rocks in 
certain definite binary combinations, — for instance, oxygen combines 
■with fourteen of them to form the most abundant rock constituents, — 
it will simplify our view of the general chemical nature of rocks and 
their minerals, if we regard these important binary compounds directly. 
I have therefore compiled the following table of twenty-one substances 
(two elements, and nineteen hinary compounds) which entirely make up 
the constituents of rocks, either as minerals themselves, or as forming 
the chemical components of minerals. To the ordinary chemical 
symbols, I have appended the abbreviated symbols generally used by 
mineralogists, and which will be adopted for the future in these papers. 
In this mode of notation, the double atom of any element is indicated 
by a liiie drawn through the sign of a single atom ; the atoms of 
oxygen are marked by dots over the sign of the other elements, and 
those of sulphur similarly by accents. 
