220 
IOWA ACADEMY OF SCIENCES. 
would direct one’s attention to the older rocks, perhaps some members of 
the Azoic series; but if the impressions seen at Sioux Falls are those of 
bivalve shells, we must look higher in the scale. But in order that we may 
arrive at an approximate conclusion, let us look at the geology of the sur- 
rounding country. 
We already know that the limestones of the upper Coal Measures are 
exposed at Omaha City, and continue up the Missouri river to a point near 
De Soto, almost twenty miles farther, where they pass from view beneath 
the bed of the river. Overlying them is a coarse sandstone composed of 
an aggregation of particles of quartz cemented with the peroxide of iron. 
This assumes every color from a deep dull red to a nearly white. The layers 
of deposition are very much inclined and distorted. Near Blackbird hill 
numerous dicotyledonous leaves have been found, and many of these plants 
occur in a quartzite so close-grained that the lines of stratification are nearly 
or quite obliterated, yet the impressions are distinct. The quartzite forms 
a valuable quarry near Sioux City. The coal included in this formation 
(Lower Cretaceous No. 1, Dakota Group) crops out forty miles up the Big 
Sioux, or within sixty miles of Sioux Falls. Between Sioux City and 
Yankton we have at least three members of the Cretaceous series. Near 
Fort James we find that two members of the Cretaceous series (Nos. 2 and 3, 
Benton and Niobrara) rest upon the quartzites. The surface features of the 
whole country, with the soil and drift, indicate that the immediate under- 
lying rocks are of Cretaceous age. Is it not impossible, therefore, that the 
quartzites that include the pipestonebed belong to the supra-Carboniferous, 
Triassic perhaps, or even to an extension downward of Cretaceous No. 1 
(Dakota Group)?” 
In the following year White* * * § gave an account of a visit to the 
pipestone quarries, having traveled up the Big Sioux river from 
Sioux City. He called attention to a number of exposures of 
the quartzite in Iowa and Dakota. 
The next year, in his report f on the Geology of Iowa, the 
same writer described at length the quartzitic formation of 
the northwestern part of the state, which he called the Sioux 
quartzite, referring it definitely to the Huronian. This is the 
first instance of giving the formation a distinct geological name 
by which it might be known. 
In the brief description of the geological features of Osceola 
and Lyon counties. White | made several references to the expo- 
sures of quartzite in the extreme northwestern corner of the 
latter county. 
In 1871 Kloos§ published some geological observations made 
in Minnesota, together with a geological map of the crj^stalline 
rocks of the state. He called and mapped the quartzite of 
southwestern Minnesota, Huronian. 
*Am. Naturalist, Vol. II, pp. 644-653. Salem, 1869. 
t Geology Iowa, Vol. I, pp. 167-171. Des Moines, 1870. 
$ Geology Iowa, Vol. II, pp. 337, 338. Des Moines, 1870. 
§ Zeitsch. D^ut. geol, GeselL XXIII Band,, p. 471. 1871. 
