APPENDIX—GEOLOGICAL SURVEY. 
465 
the fourth opening in depth has been discovered, while the fis¬ 
sures continued their downward course. 
Inasmuch as this irregular form of fissure, and consequently 
0 
irregular form of ore deposit has been the cause of a whole¬ 
sale and sweeping condemnation of this lead district, and 
has discouraged all enterprise in mining, it may be well for us to 
notice the relation that it bears to similar ore districts of known 
reputation that have passed through alternate periods of pov¬ 
erty and richness for ages, and yet supply the commercial de* 
mands of the world. Yan Cotta, in his able work on ore-de. 
posits, has arranged these districts for us, with the following 
description. 
“ Irregularly formed, more rarely vein like, in part very massive aggre¬ 
gations of galena, blende, calamine, and smitlisonite, occur in limestones 
and dolomites of very dissimilar age in upper Silesia, in Westphalia and 
Belgium, at Weslock in Baden, in the Corintliean Alps, near Anduze in 
France, in the Spanish province of Santander, as well as in the states of 
Wisconsin, Illinois, Iowa and Missouri; they are all of a similar, but by no 
means contemporaneous, origin. Great districts must have been pene¬ 
trated by metalliferous solutions, from which the precipitation of the above 
ores took place; for the greater part only in dolomite or limestone, frequently 
at their expense. 
“ To be more clear, the solution traversed the considerably fissured rock, 
and this reacted in such a way on it that carbonate of lime and magnesia 
were dissolved, the ores being deposited in their place. * * * 
“ It is altogether inadmissible to suppose that the deposition of the ores 
occurred, in these cases, contemporaneously with those of the limestone or 
dolomite; the whole manner in which the ore is distributed is opposed to 
this.” 
Ill the table of localities of this class of ore districts fur¬ 
nished by the writer, we find some of the most productive 
lead and zinc mines of Europe, such as the Derbyshire .and 
Cumberland in England, those of Aix-la-Chapelle, Upper Si¬ 
lesia, with those of France and Spain. 
In these forms of deposit, no feature is so prominent as that 
which points to a medium by which powerful solvents worked 
out places for their ores, widening the fissures in certain places, 
and leaving them almost closed in others. Heated water, with 
it’s chemical forces, urged through these strata by mechanical 
no —Ag. Tr. 
