150 
IOWA ACADEMY OF SCIENCE 
the general stratigraphic work, studies bearing upon, the subdivision of these 
special sequences of strata were at once instituted. 
The Niagaran section was finally turned over to Professor A. G. Wilson, of 
Lenox college. His delimitation* upon faunal grounds, of four subdivisions I 
am inclined to accept without material modification. The terranes as thus 
made out are recognizable over wide areas. Since the subdivisions are so well 
defined it seems proper that they should be designated by geographical names. 
The titles are taken from well-known Iowa localities where good sections are 
open to observation. 
In the case of the Senecan series (Cedar Valley limestones, etc., of many of 
the county reports) the detailed sequence of faunas was made out as long 
ago as 1887, when I was a resident of Iowa City, and was engaged in making 
a special study of the Devonic section. Essentially as then determined Calvin 
has since adopted and describedf in his report on Johnson County the several 
sections. It is only necessary to attach to them geographic names to com- 
plete their definition. These titles are taken from well-known localities in 
Johnson county where the best exposures are presented. The subdivisions 
are widely recognizable through the adjoining counties. 
Much confusion has long existed concerning the recognition and nomenclature 
of the several members of the Cretacic section of northwestern Iowa. In all 
of the early reports of the present Iowa Geologic Survey the Grill chalks and 
limestones were mistaken for the Niobrara formation. The only exception was 
my own determination of the chalks which rest directly upon the Sioux 
quartzite. 
The subdivisions of the Coloradan here recognized have all been well de- 
fined, but the names applied to the several terranes are those of the Rocky 
Mountain region. With no intervening exposures for a distance of 600 miles it 
appears very doubtful whether we are yet justified in the inference that the 
sections of such widely separated localities are identical. The western nomen- 
clature is therefore not used. In its place are proposed names of localities on 
the Bix Sioux river where good outcrops finely display each. With slight 
restriction below, the Woodbury shales of Whi,te becomes a useful and available 
name. Indeed, I am not sure but that the meaning here given to the title is 
not the one originally intended by White himself. 
The Dakotan series of the vicinity of Sioux City is now completely known, 
from deep-well borings. The lower sandstone is traceable down the Nebraskan, 
side of the Missouri river to the exposures of undoubted Nishnabotna sand- 
stone of White. The Sergeant shales and Ponca sandstone have been repeatedly 
delimited near Sioux City and up the Missouri river to Ponca and beyond. The 
latter is No. 4 of Bain’s standard sections of Woodbury county t; and the former 
includes the same author’s numbers 1 and 2 down to the massive sandstone 
beneath. 
The usage of several other terranal names should be perhaps briefly explained. 
Spergen appears to have priority over Salem, which has been sometimes used. 
Until recently the latter title was only a trade-name with no scientific definition 
whatever; the former title has been in common use for more than half a 
century. 
^American Geologist, Vol. XVI, p. 275, 1895. 
tiowa Geological Survey, Vol. VII, p. 71. 1897. 
Jlowa Geological Survey, Vol. V, p. 260, 1896. 
