424 WISCONSIN STATE AGRICULTURAL SOCIETY. 
bed (the Potsdam sandstone) which in the southern part of 
the state is covered with at least six hundred feet of lime rock? 
becomes the surface rock a little to the north of the lead dis¬ 
trict, And as we travel from the south to the north we see 
that the various beds of the different formations become the 
surface rock in regular succession. A few miles only to the 
north of the lead district, owing to the dip of the strata just al¬ 
luded to, the azoic and plutonic formation become the surface 
rock. These in the southern part of the lead district are cov¬ 
ered by at least a thousand feet of stratified rocks. 
Not to notice the fissures in the rock, and the fact that water 
w 7 ould find its way through them to the lower formations, 
water would certainly enter between the beds of these outcrop¬ 
ping strata, and find its way down the gentle declivity as nat¬ 
urally as the waters of the Wisconsin and Mississippi flow to¬ 
ward the ocean. Especially would this be the case with the 
lower bed, the Potsdam sandstone, which, where not exposed 
to atmospheric action, is but little else than a bed of sand 
through which water passes freely. 
Now let us suppose—and the facts will justify not only the 
supposition, but even the conclusion—that the elevation re¬ 
ferred to, and the belts of mineral land in the lead district were 
formed over groups of fissures or faults in the plutonic and 
azoic rocks beneath, consequently over lines of fracture pro¬ 
duced by mechanical force, evidently generated by internal 
heat. The water entering between the beds of the outcropping 
strata as above referred to, and following down its gentle de¬ 
clivity, would necessarily intersect these faults or fissures along 
the whole line. Here water would come in contact with in¬ 
tensely heated matter under a pressure of several hundred feet 
of rock. This would certainly be one of those places where 
chemical and mechanical forces would be generated, such as 
we know must have been active during the physical disturb¬ 
ance along the lines referred to, and the formation and fill¬ 
ing of mineral veins. If the temperature along the lines of 
fracture in the plutonic rocks was sufficient, the water gradu¬ 
ally or suddenly reaching the heated matter, as described, would 
