200 J. Hail on Carboniferous Limestones of Mississippi Valley. 
occurs is not a question affecting the origin of the mineral matter, 
for while in Iowa, Wisconsin and Illinois the lead-bearing rock 
is an upper member of the Trenton limestone period, it is im 
Missouri the Calciferous sandstone, a rock much older than the 
Trenton period. The mode of occurrence of the ore is simi 
in both places. : 
The fact that the calciferous sandstone in Missouri is the lead- 
bearing rock, and that sometimes in Upper Jowa and Wisconsin 
likewise less cavernous than the lead-bearing or Galena limestone, 
and far less so than the same rock in Missouri. From what we 
know, it appears that neither the Carboniferous limestone nor the 
measures ever reached so far north as the northern lead- | 
termination of the direction, it is north 40° or more west. 
In descending the Mississippi river we first notice that the 
i 
* Tn making this statement, the writer would not be understood to say that or 
ur) 
lar fissures and caverns may not have been produced in these rocks during 
. - ie 
a ox gave! of considerable difficulty. At the same time, the fissures filled w 
a matter, accompanied or unaccompanied me peculiar clay quite different from 
y alone, or with indurated clay os 
i thout the eager sandstone 
e. 
+ 
4 
