466 
WISCONSIN STATE AGRICULTURAL SOCIETY. 
force, is the only medium we can conceive of adequate to this 
work. And no doubt, one reason why these forms of fissures 
and ore-deoosits are found oftener in dolomite or magnesian 
limestones than in other rocks, is its peculiar adaptation to this 
process of mineral formation. That Van Cotta entertained 
similar views is evident from his remarks on the different 
forms of ore-deposits, which are as follows : 
“ Thus tlie formation of lodes shows itself to he not only possibly, hut 
also probably very manifold; and appears to have always stood in some 
connection with neighboring, and often shortly before, occurring eruptions 
of igneous rocks. The local re-action of the igneous fluid, interior of the 
earth created fissures; forced igneous fluid masses into many of the same; 
caused gaseous emanations and sublimations in others; and in addition, 
during long periods of time impelled the circulation of heated water, 
which acted, dissolving at one point, and again depositing the dissolved 
substances at another, dissolving new ores in their stead. The whole pro¬ 
cess is'thus not confined to any particular geological period, or any particu¬ 
lar locality, but recurs at all times, either in the same or new regions at the 
point where a re-action of the interior of the earth has taken place.” 
With these views, obtained from important ore districts sim¬ 
ilar in their origin to our own, it becomes us to scrutinize 
closely the phenomena of our fissures in their downward course, 
and to receive very cautiously, and with a certain amount of dis¬ 
trust any statement or statements made in reference to their 
closing in depth, since in these older districts actual tests have 
been made from which we may draw important information. 
In the lower portion of the galena limestone, the fissures be¬ 
come more irregular in their course, resembling in many places 
a flight of stairs. Ore deposits found in connection with this 
form of fissures are called by the miners flats and pitches. 
Where these fissures enter the blue limestone, the ore depos¬ 
its are found mostly between the beds of the strata, but always 
in connection with the fissures, and are called by the miners 
flat openings. Here the ore deposits assume a different, al¬ 
though somewhat similar form, and come much nearer to that 
of a true fissure vein in the arrangement of their material. The 
ore is formed beneath a cap rock, a very hard, compact rock, 
forming a surface over the ore very similar to the hanging wall 
