SUMMARIES OF CURRENT NORTH AMERICAN 
PRE-CAMBRIAN LITERATURE? 
Topp’? maps and gives a general description of the geology of 
South Dakota. Archean’ rocks are present in the Black Hills, near 
Sioux Falls, and near Bigstone Lake in the eastern part of the state. 
In the Black Hills the Archean rocks are slates and schists, 
intruded by granite. The metamorphic effects in the slates and 
schists become more pronounced as the contact with the granite is 
approached. Following Van Hise, it is believed that their metamor- 
phism was largely brought about by the intrusion of the granite. The 
thickness of the slates and schists is from 10,000 to 100,000 feet. In 
age they are believed to correspond to the Lower Huronian of the 
Lake Superior region. The granites, while younger than the slates 
and schists, are still pre Cambrian. 
The Sioux quartzite is similar to the quartzite of Baraboo and the 
‘Chippewa valley, of Wisconsin, and, following Irving and Van Hise, it 
is believed to be of Upper Huronian age. 
Near Bigstone Lake are exposures of granites, probably of Lauren- 
tian age. ; 
All the Archean rocks are overlain unconformably by Cambrian 
rocks which in general dip away from the Archean exposures. 
Keyes‘ gives the result of an examination of the Sioux quartzite. 
Impressions were seen at several points in the bedding planes of the 
quartzite which so much resembled those of lamellibranchs of the Car- 
dium and Cytherea types, that, notwithstanding strong pre-conceived 
notions of the ancient age of the Sioux rocks, faith in their old age 
was very much shaken. It is concluded that the Sioux formation 
should be considered as pre-Cambrian until indisputable evidence to 
t Continued from p. 753, Vol. VI, Jour. GEOL. 
2 A preliminary report on the geology of South Dakota, by J. E. Topp. South 
Dakota Geol. Survey, Bull. No. 1, 1895, pp. 172. With map. — 
3 Archean is used to designate the pre-Cambrian. 
4 Opinions concerning the age of the Sioux quartzite, by C. R. KEyEs. Proc. 
Towa Acad. Sci. for 1894, Vol. II, 1895, pp. 218-222. 
840 
