REPORT OF THE CHIEF ASTRONOMER 371 



SESSIONAL PAPER No. 25a 



average much lower than the dips of either of the other two rock-divisions. It 

 will be recalled that considerable areas, coloured on the map as ' Rossland 

 Volcanic Group,' are really underlain by the traps and greenstones of Paleozoic 

 age. The separation of these from the Mesozoic portion of the Rossland group 

 has so far proved impossible. 



The unconformities demonstrated within the Boundary belt are two in 

 number. The one occurs between the Paleozoic complex and the Mesozoic 

 members of the Rossland volcanic group and associated sediments; the other, 

 between the coarse conglomerates of Sophie mountain, etc., and the older mem- 

 bers of the Rossland volcanic group. 



- Excepting the minute crumples, folds are seldom decipherable in any part 

 of these mountains. The much broken anticline ( ?) at Little Sheep creek is, in 

 fact, the only element in the belt which shows the semblance of the arch-trough 

 structure characteristic of simpler ranges. Faults are certainly very numerous 

 but their mapping was out of the question in the time allowed for this part of 

 the Boundary section; an obvious difficulty in the way of making a useful map 

 of the faults is the general absence of horizon-markers. The primary import- 

 ance of the breaks and slips in the igneous rocks particularly to the economic 

 geology of the district is emphasized by Messrs. Brock, Young, and others. 

 The Velvet mine on the western slope of Sophie mountain is located on a zone 

 of master faulting, the dislocations occurring along a number of nearly vertical, 

 meridional faults. This zone of faults has determined the location of (the 

 western) Sheep Creek valley. Another master fault or zone of faulting is 

 strongly suspected along the axis of the deep valley of Christina lake, whereby 

 the traps on the east have been brought into contact with the Cascade gneissic 

 batholith; this hypothesis cannot >as yet be proved. 



The structural relations of the igneous bodies have already been discussed 

 in the respective descriptions of the formations. It will suffice here to note 

 the salient facts. The Trail and Coryell batholiths are typical cross-cutting 

 bodies, with the usual appearance of having replaced their country-rocks for 

 many thousands of feet of depth, in each case. The contact shatter-zone of 

 the Trail batholith is perhaps the finest, because the widest and also best 

 exposed, in the whole Boundary belt. The shatter-zone of the Coryell batholith 

 is not so conspicuous .at any point, though this body likewise encloses blocks of 

 the invaded traps and schists. Igneous bodies which have been injected without 

 replacing country-rocks in the sense of assimilating them in some fashion, are 

 extremely numerous; they include the thousands of dikes, the volcanic neck 

 ( ?) at Rossland, as well as chonolithic masses, such as the one of syenite por- 

 phyry south of the Coryell batholith, the body of abnormal olivine syenite 

 near Christina lake, and the various bodies of dunite and other peridotites. 



The whole region has evidently been under the powerful control of igneous 

 action, both volcanic and batholithic. The batholithic masses, including stocks, 

 are clearly related in their genesis to periods of intense mountain-building 

 which cannot be well dated from facts derived from this local study and must 

 be dated from analogies with outside regions. Using such additional informa- 

 25a — vol. ii — 24J 



