108 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
berg. The Mollusca, particularly Salterella [Polylopia] billingsi, suggest corre- 
lation with the Murfreesboro limestone of Tennessee. The ensemble seems best 
placed in the position of the Platteville. 
Abundance of Cryptophragmus antiquatus in Division 7 suggests assignment 
to the Pamelia, Gratton, or Witten limestones, all of which contain this peculiar 
fossil. The numerous species that occur in this division besides the Cryptophrag- 
mus do not help in correlating with the Pamelia because so few species are known 
from that formation. Not much help is to be found in these fossils of Division 7 
in comparing with the Witten fauna because no important Witten elements are 
included. The division could correlate with the Ridley or Wardell as well as 
Witten. Strophomena auburnensis suggests correlation with the Guttenberg. 
Division 8, if the reported fossils are correctly identified, is probably assign- 
able to the Guttenberg member of the Decorah formation. This is based on the 
presence of Rafinesquina cf. hermitagensis which seems to be identical with 
R. alternata Conrad=R. trentonensis (Conrad). This division also contains 
Leptaena charlottae = Bellimurina, which occurs in the Guttenberg of Minnesota. 
7. THE MISSISSIPPI VALLEY 
The Ordovician formations of the Mississippi Valley are best discussed in 
two geographic areas: the upper Mississippi Valley and the middle Mississippi 
Valley. Embraced in the former are northeastern Iowa, northwestern Illinois, 
southeastern Minnesota, and southwestern Wisconsin. The latter area covers 
parts of Missouri, adjacent Illinois, and Arkansas. 
UPPER MISSISSIPPI VALLEY 
The section in this part of the Mississippi Valley consists of the following 
section from the bottom up: St. Peter sandstone, Platteville limestone, Decorah 
shale, and Prosser limestone. 
St. Peter sandstone.—This is a widespread formation throughout the Missis- 
sippi Valley and in the subsurface of several States as far east as Indiana and 
Kentucky and west to Oklahoma. The St. Peter has generally been regarded 
of Marmor (Chazyan) age, but no clear faunal evidence has ever been accu- 
mulated to prove this point. The formation may actually be a transgressing sand- 
stone and of different age in different places as indicated on the chart. The 
known fauna consists mostly of mollusks, which are the types of animal to be 
expected in a sandstone environment. Sardeson (1896) lists the fauna which 
includes three brachiopods: ? Crania reversa Sardeson, Lingulella morsu (N. H. 
Winchell), and Orthis [Doleroides| pervetus ? Conrad. If the latter identifica- 
tion be correct, the formation would be high Porterfield and not equal to Marmor 
(Chazyan), at least in the upper Mississippi Valley. 
Platteville formation (group of Templeton and Willman).—The Platte- 
ville limestone occurs in all the States named and consists of several members 
from the bottom up: Glenwood shale, Pecatonica limestone, McGregor lime- 
stone Mifflin limestone, and Magnolia limestone. 
