POPE COUNTY. 157 
and weathering, become gray, yellow, or red. Among these clay 
shales that are associated with the coal seams the refractory clays are 
found. 
In Pope County the sandstones usually cap hills or form ridges, 
just as they do in the counties farther east and south, while the shales 
as a rule underlie the valleys. 
The sandstone ledge that forms the abrupt edge of Carrion Crow 
Mountain from Atkins to Galla Creek is widespread in western Arkan- 
sas, and was called by the Arkansas Geological Survey the Hartshorne 
sandstone, from Norristown Ridge, southwest of Russellville. This 
bed passes around the north side of Carrion Crow Mountain and 
forms the low hills from 2 to 4 miles north of Russellville. It also 
forms the rim of Tucker Mountain, from 4 to 8 miles north of Russell- 
ville, and crosses Illinois Creek to form the escarpments of Illinois 
Ridge, west of that stream. South of Tucker Mountain the rocks 
are bent into a trough or synclinal fold, and the Hartshorne sandstone 
bed is tipped up on edge to form Ouita Ridge. 
The same bed of sandstone, after passing southward beneath the 
Ouita coal basin, comes to the surface again to form Norristown 
Mountain and Dardanelle Ridge and also Reeds Ridge, northeast of 
the ferry at Dardanelle. Special attention is called to this particular 
bed of sandstone because it furnishes the key to the structural geology 
of Pope County. 
No workable coal is known in Pope County below the Hartshorne 
sandstone, though there is a bed 18 inches thick below it in Carrion 
Crow Mountain. The coal of the Ouita basin and that of the Shinn 
mines, south of Russellville, overlie it. If the Ouita bed existed about 
Carrion Crow Mountain it would be on top of the mountain, not on 
its flank. The Ouita coal bed lies south of Ouita Ridge because the 
sandstone dips southward, forming a basin or trough whose southern 
edge is Dardanelle Ridge. The Shinn mines lie north of Reeds Ridge 
because the sandstone of that ridge dips northward. 
Important beds of shale and fire clay lie both above and below the 
Norristown sandstone. The shale above the Hartshorne sandstone 
has been called the Spadra shale, because it occurs typically at the 
Spadra coal mines. The Ouita coal bed at these mines and the same 
bed at the Shinn mines is in the Spadra shale, near its base. The 
Spadra shale is mostly a clay shale, though it is usually more sandy 
toward the top, and varies in thickness from 100 to 500 feet. The 
shales on the top of Carrion Crow Mountain belong to this set of beds. 
They everywhere accompany the Ouita coal bed and dip as the coal 
dips. Starting at Illinois Creek in sec. 29, T. S X., R. 20 W., these 
shales cover the whole area lying between Ouita Ridge and Dardanelle 
Ridge and west of Norristown Mountain. Below the Ouita coal bed— 
