Geology of the St. Croix Dalles. — Berkey. 271 
A. paritts Hall. 
Aglaspis barrandii Hall. 
Dicelloc€phaliis osccola Hall. 
Illajiiinis quadratits Hall. 
In addition to these, many fragments of trilobitcs of unde- 
termined species are found. Osceola, Wisconsin, and Rapi- 
dan, Minnesota, are well known localities. Within the district 
besides the Osceola occurrence, there are a few trilobite frag- 
ments to be found in the sandstone conglomerate mentioned 
in a former chapter as the most northern outcrop of the 
Jordan sandstone. 
From the St. Lazvrence shales the following have been 
reported. . 
Dicellocephaliis ininnesotonis Owen. 
D. pcpiiie7isis Owen. 
D. spitiigcr Hall. 
Lonchocephalus chippcwacusis Owen. 
Ptychoparia an a fin a Hall. 
P. diadem a ta Hall. 
P. eryon Hall. 
P. oweni Hall. 
Lingula aurora Hall. 
L. mosia Hall. 
L. winona Hall. 
Orthis pepina Hall. 
Eiiomp/tatus I'aticinus Hall. 
Raphistoma minnesotense (Owen) Sar. 
Serpiilites iniirchisoni Hall . 
The principal localities from which fossils have been de- 
scribed are Marine Mills, Trempeleau and La Grange moun- 
tain. 
The remarkable group of fossils from near Baraboo, Wis- 
consin, referred to the Lower Magnesian by Whitfield*, evi- 
dently, as suggested by Irvingt, belong to a lower horizon. 
They will be discussed in more detail in another chapter. 
The Basal Sandstone Series. 
In Wisconsin to the southeast of this area the floor of the 
basin in which Cambrian strata lie is occupied by a great sand- 
stone bed. This is followed by a series of shales above the 
middle of the formation, which series is in turn succeeded by 
*Geology of Wisconsin, vol. IV, 1882, p. 194. 
tGcology of Wisconsin, vol. II, 1877, P- 537- 
