REPORT OF THE CHIEF ASTRONOMER 323 



SESSIONAL PAPER No. 25a 



thompsoni),' and tentatively correlates the beds with the lower Cretaceous 

 Gleickenia-be&ring strata on the Pasayten river.* The only other information in 

 hand on this question of age is that based on the condition of the stratified series. 

 It is, apparently, too greatly deformed to be placed in a post-Eocene period, 

 while, on the other hand, the degree of metamorphism is too low to warrant our 

 referring the series to the Paleozoic. Either a Mesozoic or Eocene date would be 

 preferable to either of those alternatives. Eor the present, it seems best to 

 consider the beds broadly as of Mesozoic age. 



Rossland Volcanic Group, 

 general description. 



Erom the Salmon river to the Kettle river at Cascade, a distance of forty 

 miles, the ten-mile Boundary belt contains an irregular though continuous 

 band of basic volcanic rocks. This band covers about 150 square miles of the 

 belt and is part of a volcanic area in the West Kootenay district of British 

 Columbia aggregating 500 square miles. West of the Columbia river the 

 volcanic9 are developed on the United States side of the Boundary but how 

 extensively is not known. (See Plate 32.) 



The entire volcanic area is highly accidented by basic and acid plutonic 

 masses which, in general, are younger than the volcanics and cut them. Long 

 continued erosion has revealed many of the dikes, stocks, and batholiths, so> 

 that the mapped contact-lines of the effusive rocks are extremely sinuous. 

 Owing to severe orogenic stresses the lava flows, ash-beds and breccias usually 

 have high dips and complicated structures. Most of these rocks are altered by 

 crush-metamorphism and contact-metaimorphism. They are often involved 

 most obscurely with the Paleozoic sediments just described and also with 

 younger strata which are generally unfossiliferous. The differentiation of the- 

 lavas on the ground of geological age cannot as yet be carried out systematically. 



It is certain that the volcanics were erupted in at least two different 

 periods. The oldest lavas, ash-beds, and agglomerates seem to have been 

 extruded contemporaneously with the Carboniferous limestones, cherts, and 

 slaty rocks, and have since, through regional metamorphism, been converted 

 into massive and schistose greenstones which often keep their porphyritic 

 structure more or less plainly preserved. No chemical study has been made of 

 these older volcanics, and microscopic analysis is generally helpless in the 

 attempt to refer them to definite types of lava. Erom their general habit and 

 from the nature of the alteration and metamorphic products it appears probable 

 that the whole series of Carboniferous extrusives should be classed with the 

 common augite andesites and basalts. In his reconnaissance of the region 

 during the preparation of material for the Trail sheet, HcConnell recognized 

 the Carboniferous age of these rocks and called the more massive, porphyritic 



* D. P. Penhallow, Transactions, Royal Society of Canada, Ber. iii, Vol. 1, pp. 290 

 and 329, 1908. 



25a — vol. ii — 21£ 



