1875.] 



403 



[Frazer. 



of elements actually possible, and that the ratio of the Oxygen of the 

 Silica to that of the protoxide and sesquioxide bases is only approxima- 

 tive to that of a mixture of minerals representing a mean of the highest 

 and lowest percentages of those elements which are more commonly 

 found in Basic igneous rocks. 



The same remark applies equally to the next following class : 



ACIDIC. 



PER CENT. 



Silicon 33.16 



Aluminum 6.38 



Iron from Fe^Og say 3.80 



Iron from FeO say 3.08 



Calcium 2.86 



Magnesium 1.33 



Potassium 3.34 



Sodium 3.70 



Hydrogen 0.33 



Oxygen 51.33 



Bunsen's* classes were as follows : 



PYROXENIC. 



Silica 48.47 



Alumina ^ 



Ferric oxide ) 



Lime 11. 87 



Magnesia 6.89 



Soda 1.96 



Potash 0.65 



Total 100.00 



Bringing them into the same form as the above, we have 

 PYROXENIC. 



TRACHYTIC. 

 76.67 



14.33 



1.44 

 0.28 

 3.30 

 4.18 



100.00 



PER CENT. OXYGEN. OXYGEN RATIO. 



Silicon 23.26 



Aluminum (say 15 p. c. AI2O3). 7.95 



Iron (say 15.16 p. c. FeA) ■ • • • 10-61 



Calcium 8.47 



Magnesium 4.22 



Sodium 1.45 



Potassium 0.54 



Oxygen 



Total acid and basic rad 

 icals 



0.11 j 



43.50 



56.48 



* Pogg. Ann., 1851, Vol. L.XXXIII. 



