Home > Iowa Academy of Science > Journals & Newsletters > Proceedings of the Iowa Academy of Science > Volume 46 (1939) > Annual Issue
Document Type
Research
Abstract
Masses of rock strongly resembling pebbles and boulders of granite occur in the pre-Cambrian sediments of the Black Hills about four miles west of Custer, South Dakota. These pseudo pebbles and boulders range in size from 1/8 inch up to nearly one foot in diameter, have smooth surfaces, and are well rounded. Evidence is presented that they were formed from continuous thin layers of calcareous sediment within siltstone beds. These were pinched out into small lenses during folding and rounded by rolling along shear planes. Later they were partially replaced by feldspars, quartz and micas by contact action of an intrusive granite.
Publication Date
1939
Journal Title
Proceedings of the Iowa Academy of Science
Volume
46
Issue
1
First Page
252
Last Page
252
Copyright
©1939 Iowa Academy of Science, Inc.
Language
en
File Format
application/pdf
Recommended Citation
Runner, J. J.
(1939)
"Origin of Pre-Cambrian Pseudo-Conglom-Erates From the Black Hills,"
Proceedings of the Iowa Academy of Science, 46(1), 252-252.
Available at:
https://scholarworks.uni.edu/pias/vol46/iss1/65