438 WISCONSIN STATE AGRICULTURAL SOCIETY. 
our sandstone must have commenced under the same physical 
conditions ; conditions marked by degrees of temperature vastly 
above what we find existing on the present surface of the earth. 
This view may also be strengthened by the fact that it is not 
until we rise to some distance in this formation that anv evi- 
dence whatever of vegetable or animal life appears. 
In studying the origin of the sandstone underlying the lime¬ 
stones of the lead district, or its relation to those strata, we 
should keep in view its great antiquity, and how, at that pe¬ 
riod, the crust of the earth must have been comparatively thin, 
the temperature very high, and communication between the 
interior and exterior more frequent and more abundant. 
Viewing it from this standpoint, it is a question of no little 
importance whether the evidence is in favor of its having been 
deposited by chemical or mechanical agencies; and whether 
the material entered the primeval ocean through streams trav¬ 
ersing the elevated surface alone, or in thermal waters through 
fissures traversing the earth's crust beneath. 
The Potsdam sandstone below the lower magnesian lime¬ 
stone, and the small layer above it, where it has not been 
changed by subsequent action, is only a loosely aggregated 
mass of quartz crystals, and as such is unfavorable for the 
formation of mineral veins. Because, in the first place, 
gases, steam or vapor, or water even, would pass through 
it without making a fissure; and secondly, if a fissure should 
be made through which heated water could pass, the water 
would soon dissolve the cement by which the particles are 
held together, and the result would be the filling of the 
fissure with sand. 
e If we put some of this sand on a piece of glass with a good 
reflector below it, and then examine it with a microscope, we 
can see how freely water even could pass through it, and how 
unfit it would be in this condition to present the necessary walls 
or wall-rock for a mineral vein. If mineral veins were fissures 
filled by injection, that is, with melted matter forced into them 
in a liquid state from below, and consequently formed and 
filled at the same time, there would be no reason why mineral 
