94 T. S. Hunt on Lithology. 
ili - - - - - - - 72°20 
Aulmina, - - - - - - 12°50 
Peroxyd of iron, - - - - - - 3°70 
Lime, - - - - - - - 90 
Potash, - - - - - - - 3°88 
oda, - : : ‘ - ‘ 5:30 
Volatile, - - - - - . 
99°08 
The oxygen ratio of the alkalies and alumina is 2°02: 5°84, 
or nearly 1:3. The alumina requires 43°80 parts of silica to 
form with the alkalies 65°48 parts of a feldspar having the ratios 
1:3: 12, which are those of orthoclase and albite. There will 
then remain 28-4 parts of silica. This, with the exception of a 
small amount which is probably united with the oxyd of iron 
and lime, may be regarded as uncombined. The porphyries of 
this region receive a high polish, and are sometimes’ very beau- 
potash 4-43, 
emar 
