370 FRANCIS PARKER SHEPARD 



In the southern part of the trench Daly and Schofield are not 

 in agreement as to the dividing line between the Cambrian and 

 the pre-Cambrian. In Daly's "Forty-ninth Parallel Survey" the 

 division between the Cambrian and the Beltian was placed within 

 the "clastic series" between the Altyn formation below and the 

 Hefty formation above.^ This report was based on reconnais- 

 sance work in the field, and the division of the unfossiliferous 

 formations was necessarily quite arbitrary. Schofield's more 

 detailed work in the Cranbrook area^ made changes in Daly's 

 classification and produced more evidence concerning the age of 

 the unfossiliferous series. He found Middle Cambrian fossils 

 in the Burton formation near Elko, and below this, while there are 

 no angular unconformities, there are marked signs of disconformity. 

 There is a thin basal conglomerate at the base of the Middle Cam- 

 brian, and the surface of the Roosville formation beneath is some- 

 what weathered. From these facts Schofield concluded that there 

 is an unconformity at the top of the Lower Cambrian, and placed 

 the Roosville in the pre-Cambrian. Since the Roosville is the 

 highest member of the "clastic series" (which is represented), this 

 places all of that series in the pre-Cambrian. Recently, however. 

 Colonel PolHn discovered a remarkably fine trilobite fauna in a 

 formation which is probably lower than the Roosville. According 

 to Walcott the fossils indicate a horizon at the top of the Lower 

 Cambrian. Therefore the extent of the disconformity near Elko 

 is minimized, and incidently Daly's original dividing line between 

 the Cambrian and the Beltian is more nearly correct than that 

 of Schofield. 



However, Schofield has again attempted to find an unconform- 

 able relation between the Cambrian and the pre-Cambrian.^ 

 His evidence for this includes: (i) The thickness of sediments of 

 the Siyeh formation between the Purcell lava and the basal con- 

 glomerate of the Lower Cambrian, varies from a few feet to 300 

 feet. (2) The Kthological and metamorphic contrast above and 



' R. A. Daly, Geol. Surv. Can. Mem. 38, p. 179. 



^ S. J. Schofield, Geol. Surv. Can. Mem. 76, pp. 41-52. 



3 S. J. Schofield, Science, Vol. LIV, p. 666. 



