342 DEPARTMENT OF THE INTERIOR 



[ 2 GEORGE V, A. 1912 



1 The area of the monzonite thus appears to represent the upper por- 

 tion of an igneous body in places still capped by its old rock roof or holding 

 detached portions of it. The mass is not homogeneous but is composed of 

 many varieties of what seem to be closely related types, the earliest of 

 which are generally the finest in grain and darkest of colour, while the 

 later are coarser, as if they had cooled more slowly and are more felds- 

 pathic, perhaps as the result of differentiation processes. In places the 

 intruding varieties have cut portions that apparently already had solidified, 

 since the boundaries are distinct and well defined; in other cases they 

 seem to have invaded masses still partly fluid, since no abrupt change then 

 separates the different kinds. Perhaps some of the finer masses represent 

 portions that had early solidified along the upper bounding surfaces of 

 the igneous mass and afterwards sank into the lower, more central, still 

 fluid portions. 



' No direct evidence seemed to be offered in the field as to the methods 

 by which the older sediments and augite porphyrite were removed to make 

 place for the monzonite mase; neither did there appear to be any indica- 

 tions of the absorption of material by the monzonite. Possibly the some- 

 what abrupt change in the strike of the strata respectively north and south 

 of the axis of the igneous body may indicate some more profound 

 structural break pursuing a general east and west direction and which 

 guided the upward penetrating magma and gave rise to its elongated cross 

 section. 



' The monzonite is undoubtedly younger than the Carboniferous sedi- 

 ments and associated augite porphyrite. The structural relations as shown 

 on the accompanying geological map, indicate that the igneous rock was 

 ' intruded after the major epoch of disturbances whereby the surrounding 

 rocks were tilted and folded. The date of these prominent earth move- 

 ments has already been discussed and the conclusion reached that they 

 probably took place in Jurassic times. As a result of the line of reasoning 

 adopted, it follows that the monzonite was intruded in the Jurassic or a 

 later period. That the intrusion took place not later than Jurassic times 

 is indicated by the fact that the monzonite is cut by the Nelson grano- 

 diorite, itself of Jurassic or early Cretaceous age. The deduction that the 

 monzonite body was formed in Jurassic times is strengthened somewhat 

 by the fact that within the great granite area to the north, the Nelson 

 granodiorite at times presents a monzonitic facies. Possibly the Ecssland 

 monzonite was closely connected in origin with the granodiorite and 

 appeared as a forerunner of it.' 



Mr. Connor's analysis of a specimen of the granular monzonite, taken at 

 3he LeRoi mine, resulted as follows: — 



