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IOWA ACADEMY OF SCIENCES. 
OPINIONS CONCERNING THE AGE OF THE SIOUX 
QUARTZITE. 
BY CHARLES ROLLIN KEYES. 
[xlbstract.] 
The Sioux quartzite is a formation made up of hard, flinty 
beds, of considerable thickness and extent, which are exposed 
principally along the Sioux river, in southeastern Dakota, south- 
western Minnesota and northwestern Iowa. It is of particular 
interest to Iowan s, for the reason it has been usually regarded 
as the most ancient geological formation occurring within the 
limits of the state — older than the lead-bearing rocks of north- 
eastern Iowa, and older than the Cambrian sandstones which lie 
at the base of the Mississippi bluffs in the extreme corner of the 
state. 
While most writers on the subject have agreed in assigning 
the Sioux quartzite a pre- Cambrian age, the evidence for so 
doing has usually been far from conclusive. The chief reason 
for giving this formation an antiquity greater than any other 
stratified rocks in this region has been the apparently thor- 
oughly metamorphic character of the beds and their resemblance 
to the Baraboo and other quartzites of Wisconsin and Minne- 
sota whose pre- Cambrian age is well known. But this in itself 
is far from positive proof, for Professor Calvin has lately found 
an extensive series of quartzites near the base of the Cretaceous, 
farther westward in the Black Hills region, and in all respects 
identical with the Sioux rock. 
Although the Sioux quartzite has received considerable atten- 
tion from time to time, the observations for the most partuntil 
recently have been somewhat cursory; incidental to other 
investigations rather than special examinations. 
Among the earliest published accounts of the red quartzite 
area of the Big Sioux region is that of Catlin,* the well-known 
painter of Indian portraits. Although this traveler was not the 
first white person to visit the region, he was the first to give a 
* Am. Jour. Sci., (1), Vol. XXXVIII, p. 18. 1887. 
