736 l. d. burlinc cambro-ordovician near mount robson 



Geologic Formations^ with Details as to Synonymy and 



Stratigraphy 



"robson limestones" (§23) 



(§ 23a.) The "Eobson limestones'^ are estimated by Walcott to extend 

 from the summit of Mount Eobsoii some 3,000 feet down, and are de- 

 scribed as "light gray or dove-colored and bluish gray, thin-bedded lime- 

 stones," the upper half, or 1,500 feet, being described as practically in- 

 accessible in the summit of the peak and appearing to be more massive 

 bedded and arenaceous than the beds below. 



(§236.) Two fossil localities are described, one in drift blocks brought 

 down by the "Chupo Glacier'' (61u), which is stated to "indicate a 

 horizon very close to, if not within, the base of the Ordovician,'' and the 

 other (61g) in the Extinguisher ("Billings Butte"). 



The species listed by Walcott from the drift on the "'Chupo Glacier" 

 certainly form an assemblage which the average paleontologist would 

 have little hesitancy in placing in the Cambrian, with the possibilities as 

 much in favor of the Middle as the Upper. However, one opinion re- 

 garding the actual fossils is worth more than a number of opinions based 

 on a list of species. We can only call attention to the fact that it is a 

 drift locality, to the fact that there are thousands of feet of Middle and 

 Upper Cambrian beds outcropping above the place in which it was found, 

 and to the fact that it appears to be represented in the collections at our 

 disposal from the Mount Robson region in the limestones of the Titkana 

 formation. 



(§23c.) The species listed by Walcott from locality 61q in the Ex- 

 tinguisher are described as an assemblage "of Upper Cambrian and 

 Ordovician types," which indicate the base of the Ordovician. For this 

 reason the isolated^^ Extinguisher beds are referred by Walcott to the 

 lower portion of the "Ordovician Robson limestones.^' The discovery of 

 the Extinguisher beds and fauna in the uppermost portion of the Mount 

 Rearguard section has, however, afforded us data as to the actual rela- 

 tions existing between the Extinguisher beds and the Lynx limestones, 

 and consequently between the Ordovician and the Upper Cambrian. 



(§ 23r/.) The writer secured known fossil horizons in the limestones 

 of Mount Robson 1,600 feet above the level of Berg Lake, or at an eleva- 

 tion above sealevel of about 7,100 feet. Since Mount Robson has an alti- 



^* Walcott (Ann. Rept. Smithsonian Inst, for 1915, p. 252, and Nat. Geog. Mag., vol. 

 24, 1913, p. G33, legend) speaks of a "satisfactory tie" made on the basis of dips, but 

 a visit to Mount Rearguard, which must have shared in such a visual correlation, shows 

 it not to be "Middle Cambrian," but Upper Cambrian in age, and leaves the position of 

 the Extinguisher fauna in Mount Robson open (§§ 23/, 24(1). 



