IOWA ACADEMY OF SCIENCES. 
173 
is desirable. The relative amounts of the chalk and clay in the 
same locality vary greatly, owing to the differences in the 
chemical composition of the material making up the several 
strata. The common ratio of chalk to clay is about three to 
one. A test of certain clays about Sioux City shows that a 
proper proportion could only be obtained through the mixing 
of five parts of one kind of clay or two parts of another with 
but a single part of the chalk. 
These chalks, which have been fully described by Calvin in 
various articles recently issued, are available in the northwest- 
ern portion of Woodbury county and in the southwestern part 
of Plymouth along the bluffs of the Big Sioux river. The max- 
imum thickness of the chalk is about fifty feet and the areal 
extent is so great as to make it wholly inexhaustible. In 
speaking of these chalks and clays Calvin* makes a brief 
reference to the adaptability of the materials for Portland 
cement and there certainly seems no reason why the Iowa 
material might not be used with success equal to that attained 
at other points. The most natural combination would be the 
chalk with the clay immediately under it. 
Away from the Sioux City region there are no other chalk 
beds east of the river until a point in the extreme southeastern 
township of Sac county, nearly east of Grant City, is reached. 
An exposure several feet thick of very clean, yellow to white 
chalk has been discovered here. It is not very unlike that to the 
west. The associated clays are neither so readily available nor so 
adaptable to use in cement making. It may be that further 
search will reveal splendid grades of argillaceous materials at 
this point, and if so the manufacture of cement may be carried 
on here fully as successfully as at the localities already men- 
tioned. On account of its softness the chalk is far preferable to 
the hydraulic limestone and the resulting cement is equally 
strong. 
Selenitic or gypseous cement is secured by substituting gyp- 
sum for the chalk in combinations much the same as those 
referred to; and, although no attempt has been made to utilize 
the massive mineral at Fort Dodge in the manufacture of 
cement, it would seem that it could be readily done. The avail- 
able clays in this vicinity are not like those associated with the 
chalks, but the superior grades, such as are now being used for 
common pottery, are found near by. The hardening of the 
=^Iowa Geol. Sur. Vol. I, First Ann. Kep., pp. 158 and 160, 1893. 
