REPORT OF THE CHIEF ASTRONOMER 



533 



SESSIONAL PAPER No. 25a 



The hornblende sometimes, though rarely, encloses small cores of nearly colour- 

 less augite; the latter mineral also occurs in small independent anhedra, but is 

 clearly only an accessory constituent. The other accessories are quartz, magne- 

 tite, pyrite, apatite, and titanite. The structure is the usual hypidiomorphic- 

 granular. The order of crystallization is not very clear, but much of the plagio- 

 clase seems to antedate the biotite and hornblende. 



A type specimen (]STo. 54), with the mineralogical composition just described, 

 was collected on Middle creek in the heart of the main mass. It has been 

 analyzed by Professor Dittrich, with the following result : — 



Analysis of Slesse diorite. 



Mol. 



Si0 2 56-90 -948 



Ti0 2 -84 -010 



ALA.. 18-17 -178 



Fe,0 3 1-23 -008 



FeO 5-88 -082 



MnO -21 -003 



MgO 4-36 -109 



CaO , 6-51 -116 



SrO -18 -002 



Na 2 3-23 -052 



K„6 1-57 -017 



H 2 at 110°C -12 



H 2 above 110°C -77 



P,0, -10 -001 



C0 2 -08 



100-15 

 Sp.gr • 2-793 



The calculated norm is: — 



Quartz 8-04 



Orthoclase 945 



Albite 27-25 



Anorthite 30-30 



Hypersthene 19-08 



Diopside 1-36 



Magnetite 1-85 



Ilmenite 1-52 



Apatite »31 



Water and C0 2 -98 



100-14 



The mode (Rosiwal method) is approximately: — 



Quartz 9.5 



Labrador ite 58-0 



Hornblende 12-8 



Biotite 12-5 



Augite 4-3 



Pyrite 1-5 



Magnetite •• " -8 



Apatite -5 



Titanite and zircon •! 



100-0 



