358 CHESTER K. WENTWORTH 
barrier especially on its northwest face, where at many points it 
rises in less than a mile one thousand to two thousand feet above 
the streams which parallel it. For nearly ninety miles no stream 
crosses it and in the entire distance of one hundred and twenty-five 
miles not over half a dozen roads afford passage from one side to 
the other. Its crest is the resistant conglomerate of the Lee forma- 
tion, which marks the edge of the overthrust block. Cumberland 
Mountain and Stone Mountain are composed of the same forma- 
tion, which is steeply upturned in that part of the fold common to 
the syncline and anticline mentioned above. Black Mountain and 
parts of Sandy Ridge are residual mountains left in the dissection 
of the nearly horizontal coal measures. Big A Mountain, accord- 
ing to Hinds,‘ is composed of resistant sandstones of the Rockwood 
formation, overthrust on the coal measures. 
The surface features of that portion of the block within the 
coal field are those of a maturely dissected plateau with sharp- 
crested ridges and V-shaped valleys, for the most part without 
valley flats. The surface of the pre-Carboniferous portion is 
rolling, with sink holes in the limestone portion and some, though 
not at this particular point very striking, allineation of ridges and 
valleys with the northeast-southwest trend of the Appalachian 
structure. The surface configuration of the area and the control 
of topography by the great structural features 1s admirably shown 
on the contour maps of the United States Geological Survey, to 
which the reader is referred for further detail. 
THE RUSSELL FORK FAULT 
The Russell Fork fault differs from the faults which bound the 
Cumberland block on the other three sides in that it is not a low- 
angle overthrust and that in it the greatest displacement is in a 
horizontal direction with comparatively little vertical movement. 
Its trace? is closely followed except at a few places by Russell 
tHenry Hinds, “The Geology and Coal Resources of Buchanan County, Vir- 
ginia,” Virginia Geol. Survey Bull. 18 (1918), pp. 58-59. 
2“Trace’’ of a fault is here used in its mathematical sense of the line of inter- 
section of one surface with another, i.e., the intersection of the fault plane with the 
surface of the earth. 
