Circular Patterns and Exfoliation in Crystalline Terrane, Grandfather Mountain Area, North Carolina

Abstract

Research Article| September 01, 1966 Circular Patterns and Exfoliation in Crystalline Terrane, Grandfather Mountain Area, North Carolina JOHN T HACK JOHN T HACK U. S. Geological Survey, Washington, D. C. Search for other works by this author on: GSW Google Scholar Author and Article Information JOHN T HACK U. S. Geological Survey, Washington, D. C. Publisher: Geological Society of America Received: 13 May 1965 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1966, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1966) 77 (9): 975–986. https://doi.org/10.1130/0016-7606(1966)77[975:CPAEIC]2.0.CO;2 Article history Received: 13 May 1965 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation JOHN T HACK; Circular Patterns and Exfoliation in Crystalline Terrane, Grandfather Mountain Area, North Carolina. GSA Bulletin 1966;; 77 (9): 975–986. doi: https://doi.org/10.1130/0016-7606(1966)77[975:CPAEIC]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Aerial photographs of areas of crystalline rock in the Piedmont and Blue Ridge of western North Carolina reveal numerous large-scale arcuate, circular, and elliptical patterns with diameters from 1000 to more than 4000 feet. They are commonly defined by curving streams, curving ridges, and curving belts of contrasting vegetation. Geologic mapping shows that the circular patterns are not related to primary geologic structures; circumstantial evidence indicates that they are related to exfoliation or sheeting. Rock spalls up to half a mile in diameter may be formed by dilation of the rock as the erosion surface is lowered. The spalls enable tectonic joints to open, forming thin layers of rock of differing permeability and susceptibility to erosion. Exfoliation is probably involved in the erosive process and is probably more important than has been realized, especially in crystalline terrane. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.