APPENDIX—GEOLOGICAL SURVEY. 
475 
blue limestone is known to extend beneath these mines worked 
in the galena limestone above. Whether the strata below the 
sandstone are productive or not, there is enough above it to 
last (with our present force of mining) for the next century. 
And from what we know of blue limestone and the lower por¬ 
tions of the galena limestone where they have been explored, 
we have reason to suppose that they will be equally as pro¬ 
ductive, if not more so, as that portion of the galena lime¬ 
stone which has been mined. 
The zinc deposits are mostly confined to the blue limestone; 
there are a few instances where zinc is found in the lower por¬ 
tion of the galena limestone, but they are very rare. From 
discoveries recently made, it is evident that these zinc deposits 
are the richest in the lower portion of this formation. Good 
examples of this are furnished us in the mines that are now 
being worked at Highland and Centreville, in Iowa county. 
In these mines we find galena, blende and calamine uniting to 
form the same vein ; sometimes one, sometimes the other pre¬ 
dominating. There are places, however, where the calamine 
(or dry-bone) is separated from the galena and blende, and 
formed into large bodies by itself in beds from two to three 
feet thick. 
But very few persons, either in or out of the lead district, 
seem to have any correct idea of the nature and extent of our 
zinc deposits. I speak advisedly when I say that there is zinc 
ore enough already discovered in the towns of Highland and 
Blue River to furnish (if proper encouragement was given to 
mining there) material for one zinc factory of large capacity 
for a great many years to come. And this is only one small 
place, within the limits of two townships along the line that 
separates the counties of Iowa and Grant. 
Let me state here two or three facts, (1.) The blue lime¬ 
stone, wherever it has been reached in the mines or mining 
districts that have been more or less productive in lead, has 
been productive also in zinc. Not to the exclusion of the lead, 
but thrown in as it were an associate of lead, thus to add to 
the value of the veins in this formation; an advantage we do 
