THE GEOLOGY OF MITTAGONG. 343 
Composition of the “ norm ’’:— 
Orthoclase ... 95o9'04 Pyrite... oie 10 
Albite... w. 20°44 Apatite i, 34 
Anorthite sas! tea 100 Fluorite a °O7 
Diopside Toes Oyo Carbon dioxide 1°80 
Hypersthene... 3°40 Water ... un a heat) 
Olivine Sree 65) Sa 
Maenetite ... 7°19 100°70 
Ilmenite She Ris 5597 oo 
6 
In order to obtain the “‘ mode’’ a rearrangement of the 
diopside, hypersthene, and olivine molecules to form 
aegirine and arfvedsonite would be required. 
Classification.—Class IJ., Order 5, Rang 2, Subrang 2. 
Magmatic name.—Ciminose. 
Ill. Leucocratic Gib Syenite.—This rock represents the 
marginal portions of the Gib rock syenite. The specimen 
was obtained from Saunders’ Quarry, which is about 100 
yards from the junction with the sedimentary rocks, where 
the sandstone has been converted into a glassy quartzite. 
Composition of the ‘‘norm ’’:— | 
Orthoclase ... 40°03 Apatite in aloe 
Albite ... ey Ze) Fluorite oat °23 
Noselite a a I Carbon dioxide 1°50 
Nephelite stat 40 Water... soba maneal i Ves) 
Acmite we Se —— 
Diocpside cee bs 99°84 
Olivine PRP 2: —— 
Ilmenite she 22, 
The presence of a small percentage of nephelite and 
noselite indicated by the norm, is not confirmed by micro- 
scopical investigation and so together with the diopside 
and olivine would have to be molecularly rearranged to the 
production of aegirine and arfvedsonite in the mode. 
