RUSSELL FORK FAULT OF SOUTHWEST VIRGINIA? 
CHESTER K. WENTWORTH 
University of Iowa 
INTRODUCTION 
The nature of the northeastern termination of the great over- 
thrust block of the earth’s crust, bounded on three sides by the 
Pine Mountain fault, the Hunter Valley fault, and the Jacksboro 
cross fault of Tennessee, has long been an unsolved problem to 
students of Appalachian structural geology. Many geologists have 
noted the rather abrupt ending, near the breaks of Big Sandy 
River, of the imposing barrier of Pine Mountain and its replace- 
ment to the northeastward by the irregular ridges and valleys of 
the unbroken coal field, but the manner in which the great anti- 
clinal fold and the resulting thrust fault died out has not until 
recently been satisfactorily solved. 
In 1916 Hinds,’ in his report on the Clintwood and Bucu 
quadrangles, called attention to a zone of disturbed rocks nearly 
at right angles to the general lines of disturbance in this region 
and extending partly across the trough of coal-measure rocks from 
Big A Mountain to Skegg Gap on Pine Mountain. Hinds attrib- 
uted the disturbance in this zone to the same forces that produced 
the Hunter Valley fault on the southeast and the Pine Mountain 
fault on the northwest, but he failed to perceive its significance, 
for he thought it was limited to certain areas and did not extend 
entirely across the synclinal block. 
In April, 1920, Mr. M. R. Campbell, in charge of geologic work 
in this coal field for the United States Geological Survey, called 
attention to the possibility of the belt of disturbed rocks mapped 
* Published by permission of the Directors of the U.S. Geological Survey and 
the Virginia Geological Survey. The illustrations were prepared for the Virginia 
Geological Survey. 
_ ? Henry Hinds, “The Coal Resources of the Clintwood and Bucu Quadrangles, 
Virginia,’’ Virginia Geol. Survey Bull. 12 (1916). 
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