:el.] IOWA. 147 
iging from light blue through cream to white. The lowest lime- 
>ne bed is, however, massive, white, and generally homogeneous. 
iese formations continue southward in unbroken exposures from 
d River, and, judging from analyses of very similar beds occurring 
Texas, are probably low in magnesia. 
PORTLAND-CEMENT RESOURCES OF IOWA. 
By H. Foster Bain. 
[t has already been shown that materials capable of furnishing the 
[ca and alumina necessary to the manufacture of Portland cement 
widespread, and that the location of new plants is apt to be deter- 
ned by the presence of suitable calcareous deposits and favorable 
iustrial conditions. Iowa affords no exception to these general 
les. In practically all parts of the State are shales or clays which 
ght, if necessary, be used as one of the constituents of a cement 
xture. The indurated rocks from the Ordovician to the Cretaceous 
ord shales of wide distribution and excellent character. The surface 
illations supplement these resources with loess, alluvium, and cer- 
n minor bodies of water-laid clay of glacial derivation. Material 
table for use in the manufacture of Portland cement can be found 
almost every point in the State (see PL V). 
The calcareous constituent of cements may be derived from marls, 
ilk, and limestone. All these occur within the State, though they 
} of very unequal importance. 
CALCAREOUS MARLS. 
Marl occurs in lakes which are particularly characteristic of the area 
jeered by the Wisconsin drift. The north-central portion of Iowa is 
^ered by drift of Wisconsin age," and is dotted with small shallow 
:es resembling in appearance and genesis those of Michigan. From 
le to time small amounts of marl have been reported from this area, 
I while so far no bodies of commercial importance have been located 
s not impossible that such may be found. 
CHALK DEPOSITS. 
DISTRIBUTION. 
The Cretaceous deposits which cover the western third of Iowa 
aude important bodies of chalk. With but two exceptions, both of 
ich are unimportant, outcrops of the chalk beds are confined to the 
ley of the Big Sioux River between Sioux City and Hawarden. 
e chalk beds received some attention in the course of the early geo- 
«See PI. II, Iowa Geol. Surv., vol. 11, 1900. 
