448 
WISCONSIN STATE AGRICULTURAL SOCIETY. 
Now while I would guard against these errors, held by cer¬ 
tain parties in their views of mineral strata, I would neverthe¬ 
less call special attention to the fact that certain kinds of rock 
in the same series of rocks that have undergone certain changes 
by metamorphic action, do present to the causes producing 
mineral veins and ore deposits more favorable conditions for 
the precipitation of metallic solutions than others, and that we 
do, in our mining operations, find our richest deposits in rocks 
of this character, while rocks of a different character traversed 
by the same fissures are barren of ores. 
Dolomites, or magnesian limestone, are classed with the 
rocks that present these conditions. And no matter whether 
they are the upper or lower ones in the strata, whether they 
are found in the United States, or in Europe, if they are trav¬ 
ersed by fissures, through which mineral solutions are passing, 
especially lead, or zinc, they are almost certain to contain de¬ 
posits of the ores of these metals. 
The favorable condition presented by the limestones, espe¬ 
cially the magnesian limestone, for the deposits of lead and 
zinc ores have been noticed by mining men everywhere, espe¬ 
cially in Europe; and by the largest portion of them it is sup¬ 
posed to consist in the readiness with which they yield to the 
solvents traversing the fissures, and the favorable reaction of 
these rocks on the metals present in the solution. As evi¬ 
dence of this, our attention is called to the fact that it is only 
lead and zinc that are found in any abundance in this rock, 
and that the lead is never rich in silver. Is it—asks a noted 
writer—because a very small percentage of other metals were 
present in the solution, or because these rocks reacted les3 on 
them than on the lead and zinc? 
Mineral Yeins. —No class of natural phenomena of equal 
importance has received less attention from scientific men than 
that of mineral veins. Not because it is more refractory, or 
yields with stubborness to investigation, but because it is a 
class of phenomena inaccessible to that class of men, except on 
special occasions and for special purposes. 
