Geology and Natural History. 301 
Again fissured chert beds are impregnated with lead and zine 
ores—mostly sulphides—in the vicinity of the runs and openings, 
or else alone. 
In still another variety of deposit, common in the Joplin dis- 
trict, galena occurs in loose accumulations of broken chert; an 
in part of Joplin creek valley the accumulations have a depth ex- 
ceeding 70 feet. The ore appears to have been formed in the fis- 
sures of the chert beds, and, afterward, the chert beds were 
broken up through undermining by the removal of the limestone. 
The galena extends into the masses of chert and sometimes also 
is crystallized on their surfaces, as if its deposition had commenced 
before the breaking up of the chert but was continued during its 
progress, 
There are also seams and crystals of galena and blende imbedded, 
or occupying pockets, in quartzyte, a gray to brownish and often 
bituminous variety. The quartzyte in such cases contains also 
irregular crystals of dolomite ; and the cavities left by the removal 
of this dolomite are often filled with carbonate of lead or silicate 
of zinc 
dolomization of the beds along vertical and horizontal fissures, 
this making the spaces for the ores. There are no true veins. 
States such remains seem to be frequent; but I have seen no de- 
tailed account: of them, and the only well characterized specimens 
which have come into my hands are portions of two trees from 
Ohio kindly sent to me by Dr. Newberry, and a very finely ee 
Be . 
