180 THE CLAYS OF ARKANSAS. 
On the east side of Crowleys Ridge, near the mouth of Big Crow 
Creek, and also in the bed of the creek about one-half mile from its 
mouth, there is a series of calcareous marine deposits containing 
numerous Tertiary fossils, which belong either to the Jackson or 
Claiborne horizons. The collections which have been made contain 
about an equal number of Jackson fossils and of fossils of Claiborne 
age. While the exact horizon may be somewhat doubtful, the fossils 
prove conclusively that the strata belong to the lower Tertiary beds. 
The fossils found in the strata along Big Crow Creek, east of For- 
rest City;* have made it possible to determine the age of the older 
strata along Crowleys Ridge. The ridge is, therefore, a remnant of 
the old Tertiary plain which once extended unbroken from the foot 
of the Paleozoic hills in eastern Arkansas eastward to the present 
bluffs east of Mississippi River. 
CLAY DEPOSITS. 
The clays of St. Francis County are the common brick clays found 
along the top and sides of Crowleys Ridge and the yellow clay loam 
of the prairie country west of the ridge. 
Crowleys Ridge throughout the county is capped with loess, which 
is found in different phases. In the railroad cut east of Forrest City 
there are no less than four different varieties of the loess. In places 
it is a buff to gray nonstratified mass, containing a large percentage of 
lime concretions and land shells. Both above and below lie beds of 
stratified loess, which in places is a reddish-yellow clay loam, con- 
taining little or no lime carbonate and free from shells. The yellow 
clay loams of the loess are much better adapted to brick manufac- 
ture. The bricks burn to a solid red and are much stronger and 
stand more heat than bricks made from the calcareous loess. 
The country west of the ridge has a surface covering of yellow clay 
similar to the yellow clay of the loess, but of much later age. In 
places its thickness ranges from about 15 feet at the western edge of 
St. Francis County to 40 feet or more near the foot of Crowleys 
Ridge. 
The persistency of the surface clay is shown in the following well 
sections : 
Section of well at Palestine. 
Feet. 
Red clay 12-14 
Quicksand 12-14 
White clay 6- 8 
Heavy gravel 12 
