126 THE CLAYS OF AKKANSAS. 
vician series, and are composed of heavy-bedded, dark-colored lime- 
stone and of sandstone which is doubtless the equivalent of the St. 
Peter sandstone in southwest Wisconsin and Missouri. 
CLAY INDUSTRY. 
In Lawrence County there is but one plant in the Quaternary area 
that is engaged in the manufacture of clay products. This is Moore 
& Co.'s brick plant at Walnut Ridge, where common soft-mud bricks 
are made. 
The surface white clay, to a depth of 6 feet, is used for making the 
bricks. The clay is tempered and molded in a Monarch pug mill, 
dried in covered racks, and burned in up-draft kilns. It requires 
three to four days for drying and ten to twelve days for burning. A 
light fire is kept under the bricks for five to six days, and a hot fire 
for about the same length of time. Wood is used exclusively for 
fuel. The bricks are dried and burned without checking. Wheel- 
barrows are used to convey the green bricks from the molds to the 
racks and the dried bricks from the racks to the kilns The bricks 
ha^e a shrinkage of about one-eighth of their volume. The output of 
the plant is about 1,500,000 bricks per annum. The market for the 
bricks is Walnut Ridge and the surrounding towns. 
There are two common mud-brick plants in the hard-rock district, 
one at Black Rock and the other at Imboden. The clay used at 
Black Rock is the yellow or reddish clay, doubtless of the same age 
as the yellow loam that occurs on top of Crowleys Ridge. The plant 
at Imboden uses the residual clay of the older rocks. 
LEE COUNTY. 
GENERAL GEOLOGY. 
Lee County is crossed near its center by Crowleys Ridge, which 
extends in a north-south direction. In the northern part of the 
county L'Anguille River has cut through Crowleys Ridge and joins 
St. Francis River about 6 miles southeast of Marianna. North of 
this L'Anguille River flows in the flat lands on the west side of the 
ridge and parallel to it. The eastern portion of the county is low 
bottom land, largely built up of deposits of St. Francis and Missis- 
sippi rivers. 
The typical calcareous loess forms the top and sides of Crowleys 
Ridge in Lee County. On the lower slopes on the west side of the 
ridge there is a kind of terrace or second bottom which is several feet 
higher than the flat, wet lands farther west. This terrace is very 
regular in elevation and extends entirely along the foot of the ridge 
except where it has been cut away by streams. The soil of this sec- 
ond bottom or bench is a light brown or yellow loam, the reworked 
product of the loess, and is well adapted to the manufacture of bricks. 
