REPORT OF THE CHIEF ASTRONOMER 335 



SESSIONAL PAPER No. 25a 



north of the Dewdney trail. It extends over the ridge downward into Little 

 Sheep creek valley. The fresher specimens show the presence of much olivine 

 and some undoubted chromite, but the rock has largely gone to serpentine, talc, 

 and magnetite. 



A similar irregular mass occurs on the Red mountain railway west of 

 Rossland. A large dike of rather thoroughly serpentinized dunite cuts the 

 andesitic greenstones south of Castle mountain summit, and a five-foot dike 

 of the same rock cuts the small stock of crushed granite immediately to the 

 southward. 



Since this rock is very apt to escape detection among the old volcanics, 

 it is fair to suppose that only a portion of the whole number of occurrences has 

 been discovered. The region has evidently been the scene of fairly numerous 

 intrusions of this very basic type. From the various local relations the dunite 

 has, in part at least, been injected at a relatively late date, possibly as late as 

 the Cretaceous or Tertiary, when it cut the breccias and traps of Record moun- 

 tain ridge. 



Dunite on McRae Creek. 



On McRae creek about three miles above its mouth, the section along the 

 railway crosses 350 yards of a massive, , dark, greenish-gray homogeneous intru- 

 sive which proved, on microscopic examination, to be a dunite. It cuts biotite 

 schist and a tough, old-looking andesitic breccia. The body probably has the 

 pod form. The olivine occurs in a fairly fresh anhedra varying from 0-4 mm. 

 to 2 mm. in greatest diameter. The alteration products are talc, tremolite, 

 magnetite, and a little carbonate, probably dolomite. No chromite could be 

 recognized in thin section. An analysis of a relatively fresh specimen (No. 

 528) gave Mr. Connor the following result : — 



Analysis of McRde CmeTc dunite. 



Si0 2 41-36 



TiO„ none 



AL0 8 1-21 



Fe«,0 3 9-18 



FeO notdet. 



MnO -10 



MgO 42-90 



CaO 1-34 



SrO none 



BaO none 



Na,0 -04 



K 2 -04 



H s O at 110°C -16 



H 2 above 110°C 1-94 



P 2 O s -04 



C0 2 1-40 



Cr 2 0., -15 



NiO. '15 



S .50 



100-51 



Sp.gr 3-160 



