John T. Hack
1966
<p><span>Aerial photographs of areas of </span>crystalline<span> rock </span>in<span> the Piedmont and Blue Ridge of western </span>North<span> </span>Carolina<span> reveal numerous large-scale arcuate, </span>circular<span>, and elliptical </span>patterns<span> 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 </span>circular<span> </span>patterns<span> are not related to primary geologic structures; circumstantial evidence indicates that they are related to </span>exfoliation<span> or sheeting. Rock spalls up to half a mile </span>in<span> 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. </span>Exfoliation<span> is probably involved </span>in<span> the erosive process and is probably more important than has been realized, especially </span>in<span> </span>crystalline<span> </span>terrane<span>.</span></p>
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10.1130/0016-7606(1966)77[975:CPAEIC]2.0.CO;2
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Geological Society of America
Circular patterns and exfoliation in crystalline terrane, Grandfather Mountain area, North Carolina
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