E. W. Hilgard—Geological Reconnoissance of Louisiana. 341 
et 
by the Orange Sand, whose ferruginous solutions have 
quently metamorphosed the subjacent Tertiary material into 
ferruginous shale or sandstone; at the same time forming 
above the line of contact large deposits of concretionary Brown 
iron ore,* containing from 40 to 60 per cent of hydrous per- 
oxyd, which will doubtless in time become of considerable 
practical importance. 
_ Numerous and extensive lignite beds exist in northern Lou- 
islana, the economical importance of which is already beginning 
to be appreciated. f : 
The limestones of the Vicksburg group at many points yield 
excellent lime, while the more impure varieties possess in the 
ge amount of glauconite they contain, special advantages 
for agricultural purposes. Good marls of various kinds also 
abound. These calcareous materials are the more important 
In an agricultural point of view, because the soils of the terri- 
tory, both of the Vickabaies and Mansfield groups have in gen- 
eral a foundation of pretty stiff red clay, derived from the lig- 
hitic clays, upon which stimulation produces a great and last- 
ing effect. This red subsoil may almost be considered charac- 
teristic of the uplands of northern Louisiana ; which are very 
from being “Pine Woods,” in the sense in which the ex- 
Pression is understood east of the Mississippi ; especially where 
the Vicksburg rocks underlie. 
#* Mississippi Report, 1860, pp. 23, 24. 
