6i 



tively small amount of ferromagnesian constituents. It is 

 a nearly pure nepheline rock. It is coarse in grain and 

 has a rudely foliated structure. On the weathered surface 

 there is a marked contrast between the nepheline, with its 

 smooth grey surface from which the accessory albite 

 present stands out in chalk-white grains, and the black 

 hornblende. 



Under the microscope the rock is seen to consist of 

 nepheline and hornblende, with albite, cancrinite and 

 calcite as accessory constituents, as well as sodalite, 

 apatite, sphene, biotite, pyrite and iron ore, these latter 

 mainly being present in extremely small amounts. The 

 rock is very fresh. The hornblende is a variety allied to 

 hastingsite. The calcite occurs in large individuals which 

 are found as inclusions in the nepheline and hornblende. 

 The individuals are often circular in outline and the enclos- 

 ing mineral is fresh and sharply defined against them. 

 In other cases the calcite grains lie between the other 

 constituents of the rock, but in all cases have the character 

 of inclusions. They generally show marked strain shad- 

 ows, while the other constituents of the rock show little 

 or no evidence of pressure phenomena. 



An analysis of the rock is given on p. 96. 



The "mode" or percentage mineralogical composition 

 of the rock calculated from the analysis is as follows: — 



Albite 1-83 



Nepheline 72-20 



Sodalite -28 



Cancrinite 5 • 14 



Hornblende ^'Oo, 



Hematite -50 



Calcite 3-12 



Pyrite -14 



98-30 



Water -50 



Excess of Alumina 1 -20 



100 • 00 



The rock when described represented a new rang and 

 sub-rang in the quantitative classification. 



