CURRENT PRE-CAMBRIAN LITERATURE 705 
Norton,’ in a description of the artesian wells of Iowa, discusses the 
attitude of the Algonkian floor. In the northwestern part of the state 
the Algonkian outcrops as the Sioux quartzite. From here it sinks 
rapidly to the south and east, and is discovered near the area of its 
outcrop only by the steep wells at Sioux City, Hull, and Le Mars. In 
the east-central part of Iowa is a slight elevation of the Algonkian 
floor, disclosed by the artesian well at Cedar Rapids. In Wisconsin 
the Algonkian outcrops as the Baraboo quartzite, a rock similar to the 
Sioux quartzite. From this outcrop the Algonkian sinks gently to the 
southwest, as it is reached by the drill at Lansing, Iowa. At no other 
place in Iowa has the drill gone deep enough to reach the crystalline 
rocks. 
Comment.—The connection of the crystallines reached by the drill 
with the Algonkian outcrops of Iowa and Wisconsin is conjectural, and 
perhaps it would be better not to assume that such crystallines are all 
Algonkian. However, the observations are of interest as showing the 
attitude of the ancient crystalline floor, whether Archean or Algonkian. 
Beyer? maps and describes the part of the Sioux quartzite forma- 
tion exposed northeast of Sioux Falls in sections 10, 11, 14, 15, 22, 
and 23, T. 102 N., R. 48 W., South Dakota. The quartzite dips from 
3° to 7° to the southwest. An accurate estimate of the thickness may 
not be given, but 1500 feet is a liberal one. 
Slate is exposed in the area in isolated outcrops, but never in con- 
tact with the quartzite. In composition it corresponds very closely to 
the quartz-slate of Irving and Van Hise.’ Intruding the slate are dia- 
base dikes, which have followed the bedding. 
The relations of the slates and quartzites cannot here be ascer- 
tained. However, from the relations of the two outside of the area it 
is believed that the slates are the upward continuation of the quartzite, 
and that they have been removed in large part. 
The age of the Sioux quartzite is believed to be pre-Cretaceous. 
Its reference to the Huronian may be supported by the following facts : 
The lithological characters of the quartzite are identical with those of 
Artesian wells of Iowa, by W. H. Norton: Geol. Survey of Iowa, Vol. VI, 1897 
(The Algokian, pp. 139-140). 
2 The Sioux quartzite, and certain associated rocks, by S. W. BEYER: lowa Geol. 
Survey, Vol. VI, 1897, pp. 69-112. 
3 The Penokee iron-bearing series, by R. D. InvinG and C. R. VAN Hise: Tenth 
Annual Rept. U. S. Geol. Survey, 1890, p. 370 et seq. 
