4 46 WISCONSIN STATE AGRICULTURAL SOCIETY. 
I could not doubt that the lower magnesian is a good mineral 
bearing rock.” 
These are the statements of a man who saw and studied the 
deposit, the mode of deposit, and the relation of the deposit to 
the kind of rock in which it was found; a man fully compe¬ 
tent to judge. 
I would call attention here to another error that enters into 
the belief of the inexperienced, and sometimes into the teach¬ 
ings of scientific men, namely, that mineral bearing rock or 
strata should always be productive at the surface ; and unless 
it is, it should be condemned as barren. Such views occupy 
a very prominent place in the last report of the lead district 
If the physical forces and physical conditions necessary to 
produce mineral veins and ore-deposits acted on the strata 
from above, it would be reasonable to expect large deposits of 
ore on the surface, or in depressions on the surface, or in cracks 
and crevices extending downward into the rock from the sur¬ 
face, especially if we must look to the sea for our metallic 
solutions, and to vegetable and animal remains as the precipi¬ 
tating agents. But when we take into conskLration the fact, 
or what is now acknowledged to be a fact by every intelligent 
practical man, and by every scientific man that has any prac¬ 
tical knowledge of mining, that the forces of the mineral king¬ 
dom act from below, then the fallac} 7 of such views becomes 
apparent. 
It is true we do sometimes find rich deposits of ore at or 
pear the surface. But the question is, were they formed there, 
or were they formed at great depths in the rock and subse¬ 
quently exposed by the surface being brought down to them 
by denudation. I question very much if we can find an im¬ 
portant and productive mineral district on the face of the earth, 
but that above it hundreds, and in some cases thousands of 
feet of rock have been removed by denudation since the de¬ 
posit was formed. Let us apply these views to our own lead 
district. # 
According to the statement of Prof. Whitney in the last re¬ 
port, page 125, not less than 350 or 400 feet of vertical thick- 
