176 SIDNEY POWERS 



mine, and it there presents the same appearance as on the surface 

 and in the upper workings.^ A similar dike has been found in the 

 Columbia-Kootenay mine, but the inclusions are not as large as 

 in the "White Dike." 



The sedimentary rocks of the region consist, according to the 

 map of the Boundary Creek mining district, of Paleozoic sediments, 

 some of which are metamorphic, and Tertiary conglomerates and 

 tuffs. The igneous rocks are of a number of types and represent 

 several periods of intrusion. Gneisses of questionable age occur in 

 the region, but no anorthosite has been reported. 



Three explanations may be offered for the immediate origin of 

 the inclusions: 



1. The dike-magma may have come through a thick series of 

 conglomerates of Paleozoic age and carried the pebbles and bowlders 

 upward, dissolving their cement. 



2 . The dike-magma may have intruded Tertiary conglomerates, 

 which have since been removed by erosion, the bowlders sinking in 

 the molten dike-rock. 



3. The dike-magma, when at some distance beneath the sur- 

 face may have shattered off blocks of the rocks through which it 

 passed, and carried them upward together with the blocks shattered 

 in the formation of the fissure. The friction of the numerous inclu- 

 sions against each other and against the walls of the dike would 

 remove the angles and give the blocks rounded outhnes. 



These possibilities will be discussed in order. 



1 . If there were a thick series of conglomerates in the Paleozoic 

 sediments, they should be exposed somewhere in the region, yet 

 there are no conglomerates mapped in the surrounding 200 square 

 miles (Can. Geol. Surv. Map No. 828). That the conglomerates 

 would have to be of great thickness to furnish so many bowlders is 

 shown by the known extent of the dike: 1,000 feet in length and 

 900 feet in depth. 



2. If the dike had procured its inclusions from a Tertiary con- 

 glomerate, now largely eroded, there appears to be no good reason 

 why a large majority of the inclusions should consist of a dynam- 



' This information was kindly furnished by Dr. Charles W. Drysdale, of the 

 Canadian Geological Survey. 



