REPORT OF TEE CHIEF ASTRONOMER 193 



SESSIONAL PAPER No. 25a 



' The upper part of the Cambrian system, above the Bow Eiver and 

 Xisconlith series, may thus be said to be represented chiefly by limestones 

 in the eastern part of the Laramide range, ealc-sehists in the western part 

 of the same range, quartzites, graywackes, and conglomerates in the 

 Selkirk mountains, and by volcanic materials still further to the west. 

 It is believed that a gradual passage exists from one to another of these 

 zones, and that the finer ashy materials of volcanic origin bave extended 

 in appreciable quantity eastward to what is now the continental watershed 

 in the Laramide range. Xo contemporaneous volcanic materials have, 

 however, been observed in the underlying Bow Biver or Nisconlith series.'* 



The writer has studied Dawson's original reports with a view to understand 

 the grounds of the correlations mentioned in the foregoing quotation. Unfor- 

 tunately the arduous and rapid nature of his reconnaissance surveys prevented 

 Dawson from constructing columnar sections in detail sufficient to make inten- 

 sive lithological comparisons possible. ]S!~evertheless, the more detailed facts 

 certainly seem to warrant the belief that the Selkirk series is, in the main, 

 equivalent to the Summit series of the Forty-ninth Parallel section and to 

 the Castle Mountain-Bow Biver group of ATcConnell's section. 



On the other hand, any satisfactory conclusion as to the relation of the 

 Xisconlith- Adams Lake terrane to the formations mapped at the International 

 Boundary could not be reached without further field-work. Since the forward- 

 ing of the original manuscript of this report for publication, the writer has 

 spent a season in the principal area, along the main line of the Canadian 

 Pacific railway, where Dawson studied these old rocks. At the time of the 

 present writing (Xovember, 1911), the results of that season's work are not 

 fully compiled, but certain of them, bearing on the question of correlation, are 

 already in shape for definite statement. 



The writer has been forced to differ from Dawson in several important 

 conclusions. The evidences in each case are necessarily too detailed to be 

 stated in the present report, wherein the writer's relevant conclusions only will 

 be briefly noted, as follows : — 



1. The ' Xisconlith " series of the Selkirks, as sectioned by Dawson between 

 Albert Canyon station and Glacier House, represents the northern continuation 

 of the Beltian (Belt terrane) rocks at the Forty-ninth Parallel, and conformably 

 underlies the thick quartzites of the Selkirk series, which are probably of 

 Cambrian age. The writer believes that these ' Nisconlith ' rocks of the Selkirk 

 mountains should logically be included in the Selkirk series. 



2. The 'Nisconlith' series of the Shuswap lakes area is an entirely 

 different, pre-Cambrian and pre-Beltian, group of sediments, which underlie 

 the ' Xisconlith ' of the Selkirks unconf onnably. 



* Ibid. pp. 66-7. In the second volume of the same bulletins (1891), p. 165, Daw- 

 son treats the Selkirk section at greater length, giving a structure-section and table of 

 correlations. He attributes nearly 40,000 feet of thickness to the Cambrian alone. 



25a— vol. ii— 13 



