59 



amount of apatite as an accessory constituent. These 

 minerals, with the exception of the apatite, are all in large 

 individuals, and like most of the nepheline syenites of 

 this area, have a peculiar structure which approaches an 

 allotriomorphic structure in character. None of the 

 minerals have good crystalline forms, but all have a tend 

 ency to occur with more or less rounded outlines and to 

 come against one another in curved lines. Inclusions of 

 one mineral in another are common, no definite order 

 of succession can be observed in the crystallization, and 

 the structure in some respects approaches the "mosaic" 

 structure seen in the metamorphic rocks when a complete 

 recrystallization has taken place. 



The nepheline is considerably altered to a very fine- 

 grained turbid aggregate resembling kaolin, but in places 

 it is quite fresh and shows its usual optical properties. 

 It frequently holds rounded inclusions of albite and of 

 calcite. The albite is well twinned and possesses the usual 

 characters. The hornblende is the most abundant consti- 

 tuent, and, if not hastingsite, is a variety closely resembling 

 it. It is deep green in colour and looks black on the 

 fractured surface of the rock. Although the rock is so 

 basic, it contains no iron ore, which is elsewhere common 

 as an accessory constituent in such rocks. The calcite, 

 as usual, occurs as rounded inclusions in the albite, nephe- 

 line or hornblende, or filling spaces between the grains of 

 these minerals. No microcline nor microperthite is pre- 

 sent in the sections. 



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

 the quantitative classification it ranks as essexose. Its 

 "mode" or mineralogical composition as calculated from 

 the analysis is as follows: — 



Per Cent. 



Orthoclase 2-78 



Albite 22-27! 



Anorthite 1-67/ 23 ' 94 



Nepheline I5-9H 26 . 2 . 



Kaolin 10 -'32 J "^ 



Hornblende 39 • 75 



Apatite -34 



Calcite 5 • 50 



98-54 

 Water 1 • 10 



99-64 



