40 THE CLAYS OF ARKANSAS. 
11 N., R. 4 E.; NE. J NE. 1 sec. 20, T. 10 N., R.4E.; sec. 30, T. 
16 N., R.5K; and in sec. 36, T. 19 N., R. 6 E. 
At each of these localities the fire clays underlie the lignite beds, 
and from this relation it is fair to infer that similar clays occur under 
all the lignite beds in this area. No attempts have been made to 
use these clays for making fire bricks or tiles. 
In the first-named section, which is in St. Francis County near 
the Lee County line, on the east side of Crowleys Ridge, the exposure 
is well up in the hillside, facing a small ravine tributary to St. Francis 
River. The clay is from 3 to 4 feet thick, but is difficult of access 
and extensive stripping will be required to mine it, or if a drift be 
made into the hillside it will require timbering. This clay is light 
drab in color when wet, but it dries to white or nearly white. 
The association of lignite and fire clays serves to explain the light 
color of the clays. Around all the lignite deposits in the Crowleys 
Ridge region there are extensive beds of blue or black clays, con- 
taining selenite crystals, which pass into these light-colored clays by 
hardly perceptible gradations. Some masses of lignite detached 
from great beds near at hand are imbedded in the horizontally strat- 
ified blue clays that overlie the lignite beds. The clays in contact 
with these masses are lighter colored, some of them almost white, 
having apparently been bleached by the action of the organic matter 
of the lignite. The lighter color of the underlying fire clays is due 
to the same processes. Organic matter that finds access to clays 
and soils acts as a powerful discoloring agent; from black or blue 
or even red they may be changed to drab or white. This phenom- 
enon is well illustrated along Copperas Creek in Cross County, near 
La Vesque, at the base of the great section there exposed, and also 
along the base of the Cherry Valley section, where the organic matter 
is in the form of leaves and other vegetable detritus. In Greene 
County, in sec. 35, T. 19 N., R. 5 E., and along the clay bottoms of 
Bolivar Creek, at the point where the lignite forms the base of the 
cliff in sec. 8, T. 11 N., R. 4 E., similar phenomena are to be seen. 
At the Cherry Valley locality the lignite outcrops on the surface of 
the ground, and not far away from it is an outcrop of the underlying 
fire clay. This clay forms the bed of Bolivar Creek for a distance 
of half a mile or more, passing under it and into the high bluffs 
that face it. A local dip of this bed carries it under the bed of lignite 
that outcrops in the bottom of Bolivar Creek a half mile or more to 
the west. At the locality of best exposure it passes northward 
under a cultivated field and doubtless extends entirely beneath it. 
ai quarter of a mile farther east it again appears in a thin bed higher 
m (} the hillsides, and finally disappears under a heavy talus derived 
c j a y the adjacent hills. 
