REPORT OF THE CHIEF ASTRONOMER 387 



SESSIONAL PAPER No. 25a 



intrusive holds inclusions of the surrounding rocks, and the surrounding 

 rocks are often filled with granitic material. The composition of the intru- 

 sion seems to be affected by the digested material of the rock into which it 

 has forced itself. It is also shown by the way in which the granodiorite 

 is exposed in small, more or less circular but irregularly bounded masses, 

 in different parts of the district, such as in Wellington camp and on Hardy 

 mountain. In many cases no definite boundary can be assigned to the 

 granitic mass. From the way in which the rock makes its appearance 

 in all parts of the district, it is evident that the whole of it, at no great 

 depth, is underlain by this rock. This rock has some strong resemblance 

 to the Nelson granite of the Kootenay district, both in composition and 

 in its relationship to the surrounding rocks. The Nelson granite, which 

 has been carefully studied, is a sort of granite representative of the monzo- 

 nite group of rocks, intermediate between the alkali and the lime-soda 

 series of rocks, and about on the boundary line between granite and diorite. 

 Its composition* is as follows : — 



Analysis of granodiorite- 



Pel cent. 



Si0 2 fifi.46 



Ti0 2 .27 



Al-A 15-34 



Fe 2 3 1-68 



FeO 1-83 



MgO 1-11 



CaO 3-43 



Na 2 4-86 



K 2 4-58 



H 2 .29 



P 2 B .08 



99-93 

 — Analysis by Dr. M. Dittrich, Heidelberg. 



' The Boundary Creek rock will be found on analysis to contain a 

 greater percentage of alkaline earths, but this may be due to the material 

 it has acquired from the rocks into which it has been intruded, and may 

 represent only a local peculiarity. As the Nelson granite occurs to the 

 north and east of this district and probably also to the west, the Boundary 

 Creek rock in all probability belongs to the same great intrusion. If so, 

 its age will be about Jurassic. This agrees with its stratigraphical position 

 in this district.' 



Correlation. 



There are a few certainties and many uncertainties regarding the relative 

 geological ages of the formations in the region considered in the present 

 chapter. It is known (1) that the Cascade batholith cuts the Grand Forks 



* As represented in a specimen from the Kokanee mountains, West Kootenay 

 (E. W. Brock). 



25a — vol. ii — 25i 



