112 
MUSEUM BULLETIN NO. 2. 
THE BOUNDARY BETWEEN THE LOWER AND 
MIDDLE CAMBRIAN. 
The Lower Cambrian has, by general usage, been defined as 
the time interval dominated by the Olenellus fauna, beginning 
with its earliest advent and ending with its final disappearance. 
Such a definition for the upper limit has been called in question 1 
and, as has been outlined on page 106, the Mount Bosworth 
and Mount Stephen sections in British Columbia appear to 
represent environments of so favourable a nature that Olenellus, 
or the local representative of that genus, there became tempo- 
rarily immune and did not share the timely oblivion to which 
the other members of the group appear to have been doomed. 
Chamberlin and Salisbury 2 suggest the possibility that 
Olenellus in the west may be contemporaneous with Paradoxides 
in the east, but Walcott has shown 3 the latter genus to be the 
probable derivative of a line of Olenellus ancestors including 
Nevadia , C alluvia, Holmia, and Wanneria. Schuchert 4 would 
separate the two divisions and give them systemic rank, a 
conclusion reached from a study of the relations for the continent 
as a whole; Ulrich 6 would not. 
Prior to 1905 the last traces of the genus Olenellus , the top 
of the quartzitic sandstone series, and the top of the Lower 
Cambrian were supposed, for the Cordilleran region at least, 
to be synonymous, indeed this condition appears to hold for 
Nevada and Utah as far north as Big Cottonwood canyon in 
the Wasatch range just south of Salt Lake City. Between 
this point and the Upper Columbia lakes 6 nearly 700 miles to 
the north in British Columbia, however, Olenellus is unknown, 
and the only palaeontologic evidence for the presence of the 
Lower Cambrian throughout this distance is the reference to 
that period of the Albertella fauna in the Dearborn River section 
of central Montana. That the Lower Cambrian and a con- 
1 Ulrich: Bull. Geol. Soc. America, vol. 22, 1911, p. 619. 
2 Text book of Geology, vol, II, 1907, p. 245. 
3 Smithsonian Misc. Coll., vol. 53, No. 6, 1910, p. 249. 
4 Bull. Geol. Soc. America, vol. 20, 1910, p. 483. 
6 Idem, vol. 22, 1911, pp. 625-627. 
®Dawson: Ann. Rept. Geol. Survey, Canada, for 1885, vol. 1, 1886, p. 156B, refers 
rocks at this locality to the Cambrian, but states that the included fossils were not 
determined even generically. They are preserved in the collections of the Victoria 
Memorial Museum and have been identified by the writer as Olenellus. 
