442 
WISCONSIN STATE AGRICULTURAL SOCIETY. 
the upper magnesian or galena limestone, for dolomite is the 
same the world over. 
Dolomite, or magnesian limestone seems to present very fa¬ 
vorable conditions for the deposits of lead and zinc. The rich, 
and extensive mines of Upper Silesia, Spain, France, Belgium, 
and various other places in Europe are found in this kind of 
rock. The Missouri lead and zinc mines are found in magne¬ 
sian limestone, occupying the same, or similar position in the 
strata as the lower magnesian in this state. 
We may not know fully, and consequently cannot explain 
why it is that dolomite, or magnesian limestone should present 
more favorable conditions than other rocks with which it is 
associated in the same strata. Uor can we explain fully why 
it is that any kind of rock should present more favorable con¬ 
ditions than other kinds; and yet we know it is so. Every 
miner is acquainted with the fact that a mineral vein is almost 
always affected more or less as it passes from one kind of rock 
into another. Sometimes a very rich vein, on entering a dif¬ 
ferent class or kind of rock, is suddenly impoverished; while 
on the other hand a vein may be poor while traversing a cer¬ 
tain kind of rock, but entering another kind, is suddenly en¬ 
riched. This is a very common occurrance in mining opera¬ 
tions, and the miner soon learns to distinguish between a rock 
that is favorable for mineral veins, and one that is not. It 
would save a vast amount of capital if this practical knowl¬ 
edge was more generally diffused among those who have charge 
of mining operations. 
This fact, that certain kinds of rock present more favorable 
conditions for the formation and filling of mineral veins and 
ore deposits than others, has given rise to the idea that certain 
rocks are of themselves metalliferous or mineral bearing 1 , while 
others are barren. An error has grown out of this idea that 
we would do well not only to notice, but to guard against with 
care. Many seem to think that if a certain kind of rock is 
metalliferous in one place, like soil, it is apt to be productive 
everywhere; or if it is barren in a certain place, it is apt to be 
barren everywhere. We often here men say u I have no con¬ 
fidence in the lower magnesian limestone from the fact that 
