300 The American Geologist. May, 1893 
THE RELATION OF THE CRETACEOUS DEPOSITS 
OF IOWA TO THE SUBDIVISIONS OF THE 
CRETACEOUS PROPOSED BY MEEK 
AND HAYDEN. 
By S. Calvin, Iowa City, Iowa. 
The Cretaceous deposits of Woodbury and Plymouth counties 
are composed of sandstones, shales and certain calcareous de- 
posits. The heavier beds of sandstone belong to the basal por- 
tions of the series, barely rising higher than 40 feet above the 
level of the water in the Big Sioux river. The part of the col- 
umn to which these heavier sandstones are confined is however 
not all sandstone, but consists of arenaceous beds alternating 
with beds of argillaceous shales. Above the more massive sand- 
stones the beds, for a vertical distance of 50 or 60 feet, contain 
streaks and thin layers of sand, but shales preponderate. In cer- 
tain typical exposures these alternating beds are followed by from 
thirty to forty feet of pure shales, dark in color, smooth and 
unctuous to the feel, and containing the remains of saurians re- 
lated to Plesiosaurus, teleost fishes, and, in the uppermost beds, 
impressions of Inoceramus. At the summit of the column, over- 
topping shales and sandstones alike, are the calcareous beds to 
which allusion has been made. These consist in part of soft 
chalky material and in part of more indurated, though still soft, 
beds of fissile limestone that divides under the hammer or on ex- 
posure to the weather, into relatively thin laminae crowded with 
detached valves of Jiioceramus j^^'ohlemattcus Schlot. 
In the portion of the section between the massive sandstone 
and saurian-bearing shale the beds are not everywhere constant. 
In some places thej^ contain thin bands of ferruginous concretion- 
ary sandstone. At Riverside, for example, and at the works of 
the Sioux Paving Brick Co. , there is a mass of rather thin-bedded 
calciferous sandrock in the upper part of this division developed 
to a thickness of eighteen feet. 
A generalized section of the beds along the bluffs facing the 
Big Sioux river, omitting some minute details and averaging local 
peculiarities of certain beds, would be, beginning at the base of 
the series: 
