128 
MUSEUM BULLETIN NO. 2. 
ence to the overlying division of the Cambrian that the Burton 
formation is referred with some degree of certainty to the Middle 
Cambrian. 
It is hard to resist the impression, however, that the clastic 
portion of the Burton formation may represent the Lower Cam- 
brian, and while the few species occurring in these lower layers are 
either unrecognizable or referable to types hitherto unknown, 
the suggested definition of the Burton formation will not invali- 
date its future division into shale and sandstone members. 
The Burton formation is, therefore, interpreted as a more or 
less heterogeneous formational unit uneonformably overlying the 
Pre-Cambrian, referable to the early Middle Cambrian, and 
easily separable into upper and lower members if such a division 
should be warranted by future work upon the faunas of its basal 
portion. 
SUMMARY. 
The Albertella fauna has been referred to the Lower Cambrian 1 
and this reference has been used as an argument 2 for the systemic 
designation of such faunas as that containing Olenopsis in 
Sardinia. The Albertella fauna is shown in this paper (a) to 
occupy strata transitional between the Lower Cambrian sand- 
stone and the Middle Cambrian limestone forming conditions 
of the early Cambrian, ( b ) to be unassociated with Olenellus 
though it is apparently interbedded with recurrent representa- 
tives of that genus, ( c ) to consist almost overwhelmingly of 
forms either typical of the Middle Cambrian or confined to the 
Albertella fauna as species of unknown or connecting affinities, 
and ( d ) to be referable to the Middle Cambrian. 
The Pioche formation has been consistently referred to the 
Lower Cambrian, but it is shown in this paper (a) that the 
faunal lists with which it has been credited represent an artificial 
’Walcott: Smithsonian Misc. Coll., vol. 53, No. 2, 1908, pp. 21-22. 
Idem, No. 5, 1908, pp. 203 and 212. 
Idem, vol. 57, No. 8, 1912, pp. 242 and 244. 
Mon. U. S. Geol. Survey, vol. LI, 1912, pp. 129-130. 
Smithsonian Misc. Coll., vol. 57, No. 12, 1913, p. 343. Referred to the 
Middle Cambrian on p. 338, see pages 107-109 of this paper for 
discussion. 
’Walcott, Smithsonian Misc. Coll., vol. 57, No. 8, 1912, pp. 212 and 244. 
