REPORT OF THE CHIEF ASTRONOMER 379 



SESSIONAL PAPER No. 25a 



almost completely recrystallized, so that their primary nature is often in doubt. 

 For the most part they seem to have been originally basic extrusives of andesitic 

 and basaltic character; in less degree, intrusive and dioritic or gabbroid, or sedi- 

 mentary, argillaceous rocks. These have been metamorphosed to ever- 

 varying phases of amphibolite, fine-grained orthoclase-bearing hornblende .schist, 

 hornblende-epidote-plagioclase schist, actinolite schist, and biotite-diorite gneiss. 

 Along with these, thick lenses or pods of white crystalline limestone are inter- 

 bedded. The limestone is, as yet, unfossiliferous but resembles the Carboni- 

 ferous limestone occurring about Rossland. It crops out on each side of the 

 Kettle river east of Grand Forks and is tentatively mapped as forming there 

 one large body. Mr. Brock also reports small lenses of limestone in the basic 

 schists of Observation mountain. 



Concerning the complex Mr. Brock writes (in his report for 1902, page 96) : 

 ' These rocks have a strong lithological resemblance to the Archean rocks of 

 the Shuswap series, and are the oldest rocks found in the area covered by the 

 present map-sheet, but they may possibly be more highly metamorphosed argil - 

 lites and limestones such as are found elsewhere in this district.' The present 

 writer has found no new facts with which to raise the doubt expressed in this 

 sentence, but provisionally and in the interests of greater simplicity in the 

 geological interpretation of the region, takes the second of the alternative 

 views. 



Cascade Gneissic Batholith. 



General Description. — From Cascade ;to Grand Forks the five-mile belt is 

 chiefly underlain by a relatively old intrusive body of gneissic granite which 

 extends an unknown though but short distance to the northward and an 

 unknown distance to the southward of the belt. Within the belt itself this 

 mass — the Cascade gneissic batholith — covers about forty square miles. 



Its eastern contacts with the Rossland volcanics and with the Sutherland 

 schists are hidden, so that it is impossible to state, with full confidence, the 

 relation of the granite to these other two formational groups. However, as 

 already noted, the older traps of the Rossland group are cut by a small stock 

 of crushed gneissic granite on the southern flank of Castle mountain, two miles 

 east of Cascade. While the stock granite is greatly altered it seems originally 

 to have resembled the rock of the Cascade batholith in essential respects and 

 the correlation of the two, in a tentative way, seems permissible. The Suther- 

 land schists, as exposed along the railway east of Christina lake, are traversed 

 by dikes of crushed granite porphyry which may also be regarded as possibly 

 apophysal from the Cascade batholith. At the same time, there is no means of 

 determining whether the main contacts of the batholith with these eastern schists 

 or traps are now intrusive contacts; the present contacts may have been estab- 

 lished as a result of meridional faulting along the valley of Christina lake, 

 whereby the granite has been faulted up against the trap-schist complex. 



