174 THE CLAYS OF ARKANSAS. 
The greater portion of a well close to Clark's yard, 23 feet deep, 
passed through gravel, below which lay black mud. Another well, 16 
feet deep, does not reach the black mud, but ends in the gravel. 
JOINT CLAYS. 
The next clay below the brownish-yellow brick clay is a stiff, hard 
clay having a tendency to break into small cuboidal fragments when 
exposed to the air. Its tendency to break is the chief objection to its 
use for manufacturing purposes. Ware containing any of this " joint" 
clay, as it is called, is likely to break in drying. 
This joint clay varies somewhat in different places as regards color, 
having a blue or red tint according to its position, but the color has 
no apparent effect on its texture or its tendency to break when exposed 
to the drying action of the atmosphere. It appears to be very per- 
sistent, being found in nearly every opening in the district that passes 
through the upper beds. It is not confined to the brownish-yellow 
brick-earth area, but underlies the chocolate clay and some of the 
gravels. 
In the district north of the river this joint clay is red and is seen 
in the stream running through the small bayou on the north side of 
Big Rock, where it underlies 2 feet of chocolate clay. In the wagon 
road near the Fort Smith crossing of the St. Louis, Iron Mountain and 
Southern Railway it varies from 3 to 5 feet in thickness and overlies 
a red sandy clay. In Mr. Vestal's portions of sees. 26 and 27, T. 2 N., 
R. 12 W., it lies near the surface. In the NE. \ N.E. \ sec. 17, T. 2 N., 
R. 11 W., the clay underlying the brownish-yellow loam is very com- 
pact. 
In the NE. \ NW. \ sec. 21, T. 2 N., R. 11 W., the clay underlying 
the brownish-yellow loam is a whitish-yellow and blue mixed sandy 
clay 20 feet thick and rests upon 12 feet of mottled clay. 
On the south side of the river a blue clay underlies the other clays 
at most places where deep cuttings have been made. This clay, 
which lies just below the brownish-yellow surface clay, is a light-blue 
iron-stained clay containing quantities of pebbles and sand and 
nodules of limonite. 
The underlying clay on the corner of Rector avenue and Eighteenth 
street is bluish gray and contains pebbles. At this place it is 19 feet 
thick. It is also seen in the bank of a small stream a short distance 
south of this place. 
At C. Clark's old brickyard the brick earth is also underlain by this 
light-blue sandy clay. This same blue clay extends southward over 
the ground formerly used as a brickyard on the south side of Twenty- 
fifth street. 
In the banks of the small stream that runs through the cemetery 
and westward across the Sweet Home kirnpike, close to the Confeder- 
ate soldiers' cemetery, there is a heavy deposit of a stiff, red joint clay. 
