Geology and Natural History. 149 
Joplin mines. Analyses of oe from nine different localities, 
show an average of a little over an ounce of silver to the ton 
part of the lead as carbonate on the inside of the coating, but 
carrying most of it out of the shell, either to deposit it fined 
ately or to car sal it away. When this process has been continued 
for some tim find a round or oval shell of compact and gen- 
eel pibense 2 cerussite, of the size of a walnut, or sometimes 
heavy beds. The greatest observed thickness is 105 feet. This is 
here one of the principal ore-bearing rocks, containing galenite in 
humerous sheets or seams. It is evident, in all places, that the 
galenite was formed after the chert hac been formed and hardened 
and in many places broken up. The limestone has undergone, in 
many places, a process of dolomization. Solutions ate? it 
have dissolved the carbonate of lime and partly — ao it with 
carbonate of magnesia. ith this shade a contra con 
nected ; cracks are opened in the mass, and filled with prnauiel 
dolomite. The change was always begun either in fissures or on 
the surfaces of layers or of broken off blocks, and gradually pro- 
ceeded toward the interior of the rock. It seems to have preceded 
irregular outline gen ae from two to six feet high, above whial 
the solid beds e undisturbed. In the Joplin districts, the ore- 
rian Tend reso though ariy. she in the Bees pliopiteras as are 
all those of the southwest portion of the State. None of the 
posits as yet ca = have proved to be paying to a greater depth 
than about 80 feet below the surface. his fact is independent of 
