148 
CEMENT MATERIALS AND INDUSTRY. 
[BULL. 
logical surveys of the region, and have been recently restudied bj 
Calvin/' Bain,* and Wilder/ 
The chalk forms prominent bluffs at intervals and may be well-set 
near Westfield, Akron, and Hawarden. It was referred to the Ni< 
brara formation until Wilder discovered fossils characteristic of tl 
Benton in the shale above. This proves that the Iowa chalk is tl 
equivalent of the " Oyster Shell Rim" of the Black Hills or tl 
Graneros limestone. 
THICKNESS. 
A thickness of 20 to 30 feet is ordinarily seen in individual exp( 
ures, but a total thickness of 50 feet is probably present. A genen 
ized section may be given as follows: 
Section of chalk beds. 
1. Chalk 
2. Limestone, soft, splitting into thin slabs and crowded with shells of 
Inoceramus ..: 
3. Chalk 
COMPOSITION. 
The interbanding of thin-bedded limestone with the chalk, as sho^ 
in the foregoing section, is quite characteristic. Both materials ai 
soft and grind easily. Almost no magnesia is present, as is shown 
the following analyses, and in some instances the chalk beds thei 
selves carry enough or more than enough clay to make a good cemei 
mixture. In all cases excellent clays occur immediately above 
below. The clays are now being used at Sioux City and elsewhere 
the manufacture of a wide variety of clay products. 
Analyses of Iowa chalks. 
Silica (Si0 2 ) and insoluble 
Iron oxide and alumina (Fe. 2 3 and A1 2 3 
Calcium carbonate (CaC0 3 ) 
Magnesium carbonate ( MgC0 3 ) 
Water 
22.70 
6.68 
64.30 
5.38 
83.70 
2.48 
.08 
94. 
1. Chalk rock, Hawarden, Iowa. Newberry, analyst. 
2. Chalk rock, Westfield, Iowa. Weems, analyst. 
3. Chalk rock, Lemars, Iowa. Weems, analyst. 
a Calvin, S., Cretaceous deposits of Woodbury and Plymouth counties, etc.: Iowa Geol. Survey, 
1, 1898, pp. 147-161. 
fcBain, H. F., Cretaceous deposits of the Sioux Valley: Iowa Geol. Survey, vol. 3, 1895, pp. 101- 
Geology of Woodbury County, ibid, vol. 5, 1896, pp. 273-275, 295-296; Geology of Plymouth Coui 
ibid, vol. 8, 1898, pp. 354-360. 
c Wilder, F. A., Geology of Lyon and Sioux counties: Iowa Geol. Survey, vol. 10, 1900, pp. 111- 
151-152. 
