52 



THE GEOLOGIST. 



increase 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 . , 



2. Hydrogen . 



3. Carbon. . 



4. Sulphur . 



5. Chlorine . 



16. Iron 



0. 



6. 



Fluorine . . 



Fl. 



11. 



Magnesium 



. Mg. 

 Ba. 



H. 



7. 



Silicon . . 



Si. 



12. 



Barium . 



C. 



8. 



Boron 



B. 



13. 



Potassium. 



. K. 



s. 



9. 



Aluminium . 



Al. 



U. 



Sodium . 



Na. 



CI. 



10. 



Calcium . 



Ca. 



15. 



Lithium . 



Li. 



Fe. I 17. Manganese 



Mn. 



XIII. 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 iu 

 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 binary 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. 



