EARLY CAMBRIAN STRATIGRAPHY. 
129 
mingling of Lower and Middle Cambrian forms, (&) that 
the formation is divisible in the Big Cottonwood Canyon and 
Oquirrh Range sections of Utah into a true Lower Cambrian 
horizon with Olenellus (the Olenellus gilberti zone) and a Middle 
Cambrian horizon which is called the Bathyuriscus productus 
zone and correlated with the Spence-Stephen-Titkana faunas, 
and (c) that it is probably divisible near Pioche, Nevada, 
the type locality, into a true Lower Cambrian horizon with 
Olenellus (the Olenellus gilberti zone) and a Middle Cambrian 
horizon with Crepicephalus (the Crepieephalus zone) which 
is tentatively correlated with the Albertella fauna and the 
Burton formation. 
The Burton formation of Schofield 1 has in this paper received 
its first palseontologic treatment: its section near Elko, British 
Columbia, is given, its faunas are listed, and it is correlated 
with the Albertella fauna and referred to the early Middle 
Cambrian. 
The Lower-Middle Cambrian boundary has heretofore been 
drawn above the youngest beds containing Olenellus , irrespective 
of conflicting diastrophic and organic evidence. It is in this 
paper redefined and drawn at the base of such horizons as the 
one containing the Albertella fauna, a suggestion which is 
believed to accord with the principle that the inauguration 
of major units in the stratigraphic series is more closely related 
to the phenomena attending depositional expansion and the 
introduction of new faunas than to the accidental and senile 
lingering of a decadent type. 
Kleol. Surv., Can., Museum Bull. No. 2, 1914, p. 82. 
