6o 



(2) Nepheline syenite (2nd variety). 



This is rich in nepheline and contains a large percent- 

 age of pyroxene. It is much lighter in colour, but other- 

 wise bears a general resemblance to the variety just des- 

 scribed. Under the microscope all the constituents are 

 seen to be fresh, but they frequently show signs of having 

 been submitted to pressure, as shown by the presence of 

 a more or less uneven extinction. This is especially marked 

 in the case of the calcite, and the albite can in some few 

 instances be seen to have been not only bent but actually 

 fractured. The nepheline also occasionally shows strain 

 shadows. As before, no microcline nor microperthite is 

 present in the sections and a Thoulet separation shows that 

 the rock contains no potash feldspar. The albite has a 

 specific gravity of very nearly 2- 61. 



The pyroxene is very deep green in colour and slightly 

 pleochroic. Around the individuals of this mineral and 

 occasionally about the calcite grains, there is sometimes a 

 narrow border of garnet. The pyroxene is evidently very 

 rich in iron and holds rounded inclusions of calcite and 

 nepheline. 



An analysis of the variety is given on p. 96. Under 

 the quantitative classification it ranks as vulturose. Its 

 "mode" or mineralogical composition as calculated from 

 the analysis is as follows: — 



Albite I9-39 



Nepheline 50-57 



Pyroxene 18-35 



Garnet 1 • 45 



Iron ore 1-86 



Apatite -34 



Calcite 6 • 80 



98-76 

 Water -88 



99-64 



(3) Monmouihite (3rd variety). 



This is the type locality for this rock which is allied 

 to urtite, but differs from that rock in containing a rela- 



