32 THE CLAYS OF ARKANSAS. 
a few inches of the surface soils are stripped off and used, care being 
taken not to go too deep into the subsoil, which is too stiff to mold 
well with the processes employed, and which is, besides, but little 
different from the ordinary limonitic or hardpan clays of the bottoms. 
This soil extends out from the ridge toward the east, surmounting 
the low divides between the numerous drainage areas. The soils 
higher up in the hills contain more loess clay and less limonite, but 
commonly more sand. 
With such marked differences in the characters of the slope soils 
or clay at localities very near one another, it is not surprising that 
the bricks produced exhibit every degree of color, finish, hardness, 
and durability. 
CLAYS AND KAOLINS OF CHEMICAL ORIGIN. 
It has been stated that kaolin was derived directly by decompo- 
sition of feldspathic rocks. While this is true in a general way, all 
kaolin is not made in this way. It occurs in small quantities in 
regions of Paleozoic rocks, where it forms thin bands or fills small 
pockets. In these places it seems to have been formed by chemical 
action. It is true that kaolin is practically insoluble, but certain 
forms of silica are equally insoluble, yet these very forms are soluble 
under certain conditions if time enough is allowed for solution. The 
same is doubtless true of kaolin, otherwise we should not have deposits 
which are far removed from the original feldspathic rocks and which 
can be explained by no other theory. Either kaolin is soluble in 
some substance or under certain conditions of which we are as yet 
ignorant, or it is soluble in the waters that usually traverse the rocks 
when plenty of time is allowed for reaction to take place. 
In any case the kaolin (newtonite) found in small pockets in the 
rocks of the northern part of the State was not deposited as a sedi- 
ment as were the shales and sandstones and limestones of that region, 
nor was it derived by decomposition directly from feldspathic rocks, 
but it is a secondary deposit, derived by chemical action from the 
sedimentary beds above and about it. a The same is true of rec- 
torite, which occurs in Garland County. 
BAUXITE. 
The pisolitic clays and kaolins associated with the bauxites of 
Arkansas, in so far as their origin is understood, do not appear to 
fall under any of the foregoing classes. Their composition varies 
from that of an iron ore carrying 55 per cent of metallic iron to that 
of a true kaolin with but little or no iron. In some places they pass 
by gradual transition into true bauxite — that is, a hydrated oxide of 
a See Chapter III of this report, p. 34. 
