SEBASTIAN COUNTY. 201 
afterwards became coal. Subsequently all these beds have been 
pressed into folds, lifted into dry land, and in many places worn away. 
The sandstones are in some places coarse enough to be considered 
grits or conglomerates, while the shales in places grade over through 
sandy shales to fine sandstones. The coal is confined to the upper 
portion of the Carboniferous rocks in Sebastian County, but the clay 
shales cover a larger area than the coal. 
The sequence of the rocks varies from place to place owing partly to 
the fact that the folding and erosion of the beds has left one set of beds 
at the surface at one place and another set at another. Moreover, the 
horizontal variation of the beds or the grading of fine sediments into 
coarser ones results in a variation in the sequence of the beds, espe- 
cially when the sections considered are several miles apart. 
In the process of denudation (the weathering and breaking up of 
the rocks and their removal by streams) the shales decompose, 
readily forming clays, while the sandstones, as a rule, are more resist- 
ant. The result is that the valleys are usually cut in the shales, 
while the sandstones are left capping the hills if the beds are horizon- 
tal or forming long winding ridges if the beds are folded. In Sugar 
Loaf Mountain and in Jennings Mountain the beds are nearly hori- 
zontal, and these mountains are capped with sandstone, while in the 
long, narrow ridges, like Long Ridge, just north of Jenny Lind; Sand 
Ridge, running from Hackett City to Greenwood; Nigger Ridge, 
southwest of Huntington, and Devils Backbone Ridge and the other 
parallel ridges south of Greenwood, the resisting beds are sandstones 
that have been thrown into folds and then eroded. Inasmuch as the 
clay shales are interbedded with the sandstones the valleys curve 
with and follow the ridges, and it is in the valleys that the shales are 
usually found. At some places the shales are decomposed into soft, 
plastic pottery clays, as noted later, but more frequently they are 
compact, or fissile, breaking up under the influence of the weather 
into small, angular fragments. 
One of the most important manufacturing interests of the State is 
based on the clay shales of the coal-bearing rocks of Sebastian County, 
which are used in the manufacture of paving bricks. This industry 
began under circumstances not without interest. In 1889 the citizens 
of Fort Smith had under consideration the paving of their streets, and 
the State geologist of Arkansas received a letter from Harry E. 
Kelley, the chairman of the paving committee, asking his advice in 
regard to the best clay of the region about Fort Smith for the manu- 
facture of paving bricks. The State geologist visited Fort Smith and 
examined the clays and clay shales near that city. He found that 
attempts had been made to manufacture paving bricks from the 
sandy clays and loams of the river terraces, but these bricks were, of 
course, too soft to be available for paving streets. It was pointed out 
