200 
IOWA ACADEMY OF SCIENCE 
As here defined the Niobrara chalky limestone is not the so-called 
Niobrara chalk commonly noted in Iowa by Meek and Hayden, Calvin, 
Bain, and others,, but a bed much higher in the section which has been 
recently directly traced in the field to the typical outcrop of the Nio- 
brara limestone. It has a very small areal extent within the boundaries 
of Iowa. This member has quite generally escaped observation. 
The Hawarden shales are tentatively referred to the Pierre shales in 
the early Iowa geological reports. In some of the reports of the Federal 
government these beds are called the Carlile shales and they are con- 
sidered the exaqt representation of the similarly named shales in Colo- 
rado. There appears to be no valid grounds for such reference except 
the very uncertain one of lithologic similarity, or similarity of lithologic 
sequence. Until there is better evidence forthcoming than now seems 
possible it appears best to designate the Iowa beds by a distinctive title, 
by a name from the town where the formation is well exposed, and 
at which the section has been fully described. 
The Crill chalk, or limestone, is the well-known formation exposed 
at various points above Sioux City, especially near Westover and the 
old site of the Crill mill. It is this layer which has usually gone by 
the name of the Niobrara chalk — a correlation and mistake which Meek 
and Hayden first made and which the majority of later writers followed. 
Others have correlated the formation with the Greenhorn limestone of 
the Rocky Mountain region. It is the Inoceramus limestone of White. 
With slight modification of limits the Woodbury shales of White seem 
to be a useful subdivision. The formation has been so long recognized 
without challenge that it appears proper to retain the title for the Iowa 
section rather than to try to adapt the much later named Colorado sec- 
tion under the term Granieros shales. 
The Ponca sandstone is the massive bed so well displayed near Sioux 
City, and on the opposite side of the Missouri river, especially at the 
village of Ponca. At Sergeant Bluff this layer forms a prominent 
ledge; and at Crill mill it lies at the water’s edge. 
Beneath the massive sandstone of Ponca are 75 feet of sandy and 
argillaceous shales. They are best exposed at Sergeant Bluffs, six miles 
below Sioux City on the Missouri river. Farther downstream they also 
outcrop, particularly on the Nebraska side of the river. 
On the Iowa side of the Missouri river the lowest sandstone appears 
to be hidden for a distance of many miles. Recent wells put down in 
the vicinity of Sioux City clearly show that this sandstone is quite 
massive, and homogeneous in character, and has a thickness of fully 
