Sioux City Academy of Science and Letters. 161 
taining that these clays are the equivalent of those across 
the Missouri in Woodbury County, Iowa, mapping them 
on the areal geology map, and making an investigation 
of the fire clay in connection with the lignite deposits, no 
detailed study of these clays was deemed necessary at 
present. The great development of the clay industries 
at Sioux City and Sergeant Bluffs, Iowa, has demon- 
strated the value of these clays and at the same time it 
has so preoccupied this field that for many years there 
will be no opportunity for successful competition in the 
manufacture of staple clay goods in Dakota County. The 
possibility of making fire brick will be mentioned later.? 
CEMENT. 
One industry, the manufacture of Portland cement, 
as yet untouched in this immediate vicinity, is a possi- 
bility in Dakota County. At Yankton, South Dakota, an 
excellent grade of Portland cement is made from 4 parts 
of Niobrara chalk to 1 part of the overlying Pierre clay. 
The Pierre clay does not extend as far south as Dakota 
County nor does the Niobrara chalk, but the chalky beds 
of the Greenhorn limestone in connection with the under- 
lying dark argillaceous Benton shales near Sioux City 
have been found by analysis to contain the requisite 
ingredients for a good cement. Experiments showed 
that the use of 5 parts of one kind of clay to 1 of chalk, 
or 2 parts of another clay to 1 of chalk, would be the 
proper proportions for the mixture. Dakota County con- 
tains an inexhaustible supply of the chalk and clays, 
especially along the bluffs north of Jackson. There is no 
railroad nearer than at Jackson, but a spur 3 or 4 miles 
long from either of the two roads at Jackson could very 
easily be constructed over the flat bottom land right to 
the very center of the deposits. 
Cement will eventually be made in this vicinity, for 
the plant at Yankton can not supply the demand from 
this rapidly improving part of the country. Whether the 
industry will be located in Nebraska or in Iowa depends 
upon where the first start is made. 
aFor fuller notes on the clays of this region see Bain, H. F., Geol, 
Woodbury County, Iowa Geol. Survey, Vol. 5, 1895. 
bLonsdale, E. H., Cement materials in Iowa: Proc. Iowa Acad. 
Sci. for 1894, Vol. 2, 1895, p. 178. 
11 
