190 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



by Walcott.* The whole Purcell series as shown in Tahle IX. is certainly 

 placed by Walcott much too low in the geological scale. His reason for making 

 that particular correlation was probably in part due to the following statement 

 of the present writer's in his summary report for 1904 (p. 97) : — 



' The nearest relatives of the Creston and Kitchener quartzites in the 

 Rockies are respectively the two thick members of the Altyn limestone 

 delimited by Mr. Bailey Willis, who, in the year 1901, carried out a recon- 

 naissance survey of the Boundary belt on the Montana side.' 



The expression ' the nearest relatives ' should have been ' the nearest 

 lithological relatives,' as the intention was to note the lithological relations 

 of the Purcell and Lewis series, rather than to imply equivalence of age among 

 individual members. As a matter of fact the Altyn formation is believed to be 

 the stratigraphic equivalent of a part of the Creston quartzite. On the . other 

 hand, we have seen that the facts point towards the correlation of the Kitchener 

 quartzite with the Siyeh and Grinnell formations of the Lewis series. 



The somewhat elaborate correlation Table VIII. is intended to illus- 

 trate a suggestion rather than a proof. The unfossiliferous rocks of the 

 Forty-ninth Parallel were approached by Dawson, McEvoy and others from 

 the north, where lithologically similar formations bear Cambrian fossils; and, 

 somewhat naturally, regarded the thick quartzites, etc., to the south as probably 

 Cambrian. The United States geologists have as naturally refused to place 

 the nearly unfossiliferous Belt terrane in the same part of the geological column 

 as the formations of Utah and Nevada, where Cambrian fossils are not rare. 

 The present writer has had to rely chiefly on lithological characters in making 

 correlation and his tentative conclusion may be ultimately proved to illustrate 

 once again the danger of using this criterion. It is certain, however, that the 

 pre-Cambrian age of the Belt terrane is not proved, and we are yet at the stage 

 where all reasonable correlations should be fully stated and carefully examined. 



By the writer's suggested view the Eastern half of the Cordillera carries 

 a simple Paleozoic-Beltian geosynclinal prism which is only locally interrupted 

 by unconformities. The pre-Ordovician thickness of this prism has an observed 

 maximum of about 30,000 feet. According to the view of Walcott and his 

 former colleagues in the United States Geological Survey, the Eastern belt 

 of the Cordillera carries what may be called a compound geosynclinal prism, 

 made up of a pre-Cambrian series reaching observed thickness of about 30,000 

 feet, separated by a strong erosion unconformity from a Cambrian series reach- 

 ing a maximum observed thickness of at least 20,000 feet. The pre-Ordovician 

 sedimentaries, excluding such huge series as those represented in the Priest 

 River terrane, the Cherry Creek beds of the Belt mountains, the Red Creek 

 quartzite of the Uinta mountains, etc., are thus credited with some 50,000 

 feet of maximum thickness. 



By the writer's view the Eastern Cordilleran belt (including the Great 

 Basin), from the Yukon boundary to northern Arizona, was the scene of 



*Bull. Geol. Soc. America, Vol. 17, 1906, p. 18. 



