20 J. H. Kloos—Cretaceous Basin in the Sauk Valley. 
est. ope soon to have an opportunity to compare them with 
similar rocks, which in Germany have been the subject of elabor- 
ate chemical and mineralogical investigations, and expect to ~ 
come to very interesting results. As yet I have had no occasion to 
determine the nature of the feldspar and the species of pyroxene, — 
though I expect to find labradorite, anorthite and hyperite, with 
hornblende, mica and perhaps protobastite the principal con- 
stituents. : 
The Sauk river cuts 30 feet deep into the prairie at Rich- 
decomposed granite of a white and light-reddish color. At 
another point on the river, a thin seam of iron ore, impure 
peroxide of iron, runs through the strata, and a few feet above » 
the conglomerate a thin seam of an impure lignite can be seen. 
All these strata lie apparently horizontal. They belong to an 
older period than the Drift formation, and, as I will show further 
on, are part of the eastern extension of a Cretaceous basin in the 
old crystalline rocks, which extend south and west, and is prob- 
ably connected with the Cretaceous basin of Dakota, so exten- 
sively developed on the Missouri river. 
The banks of the Sauk river do not throw much light upon 
the age of the strata, the plastic clay having only furnished me 
the small tooth of a Carcharodon. The shaft and borings, 
found in the Benton group, but the development and nature of 
the deposits are entirely similar. In both localities they con- 
