REPORT OF TEE CHIEF ASTRONOMER 191 



SESSIONAL PAPER No. 25a 



generally uninterrupted] sedimentation through Cambrian time. Walcott's 

 correlation involves the conclusion that a. very large area included within 

 southern British Columbia and Alberta, much of Idaho and of western Montana, 

 represents more or less continuous land (Belt terrane), separating the Cambrian 

 basin of the Canadian Rockies from the Cambrian basin of Utah and Nevada. 

 These fundamentally different conceptions are important not merely in strati- 

 graphy ; they should be in the mind of anyone who attempts to decipher the 

 conditions under which orogenic forces built the ranges of the Great Basin 

 and the Front ranges of Montana and Alberta. 



Correlation with Dawson's Selkirk and Adams Lake Series. 



Shortly before his death George M. Dawson read before the Geological 

 Society of America a paper summarizing his views regarding the geology of 

 the Canadian Cordillera.* It is fortunate for the science that he was enabled 

 to complete this able review of his discoveries during a quarter of a century 

 of nearly continuous exploration in the mountains. In the delicate and 

 principal matter of correlation no other person could have so authoritatively 

 digested Dawson's numerous reports along with the others published before the 

 year 1900. The reader of his summary will note how Dawson used his accus- 

 tomed scientific, caution in making correlations among the older rocks of 

 British Columbia. In so brief a review of a vast area it was inevitable that 

 all of his doubts and qualifications could not be expressed. Still more in his 

 original government reports he shows how other interpretations might be 

 deduced as field work progressedi Somewhat different correlations are, in fact, 

 suggested by the field data at the Forty-ninth Parallel. The present writer 

 believes that the lithology of those sections as described, is sufficiently similar 

 to that of the Forty-ninth Parallel formations to warrant certain tentative 

 correlations within the Selkirk mountain system. Where all is so difficult in 

 the study of these unfossiliferous groups of strata, it is well to entertain all 

 possible views of the relations until accumulating facts shall narrow down the 

 alternatives. 



Dawson had found in the Selkirk range and the ' Gold ranges ' (the 

 Columbia system of the present report) three thick groups of rocks, which 

 he named the 'Nisconlith series,' the 'Selkirk series,' and the 'Adams Lake 

 series.' All three were referred to the Cambrian and each series was regarded 

 by Dawson as a stratigraphic equivalent of some part of the Castle Mountain- 

 Bow River group of the Rocky Mountain range. For the purposes of the 

 present discussion no briefer, more accurate way of presenting Dawson's salient 

 conclusions concerning these series can be devised than to quote his own 

 summary in full. He wrote : — 



' Passing now to the next mountain system, to the southwest of the 



Laramide range and parallel with it — the Gold ranges — we find in the 



* G. M. Dawson, Bull. Geol. Soc. America, Vol. 12, 1901, pp. 57-92. 



