422 WISCONSIN STATE AGRICULTURAL SOCIETY. 
is to accept the latter as the cause. This key will doubtless 
explain most of the phenomena along this elevation of land, 
and perhaps throw considerable light on our mineral veins ; 
but I forbear using it for the present. 
There is another class of phenomena that i would briefly 
refer to in connection with this topic, and which bears perhaps 
a closer relation to it than we may at first suppose, namely ; 
the chimney-like perforations we sometimes observe in the 
sandstone. This class of phenomena is noticed only by a close 
observer; in fact the chances for observation are few, for this 
rock is exposed only at its out-crop along the streams. Where 
the rock is opened as a quarry, we sometimes meet with good 
examples. These perforations (or what were once holes in the 
sandstone made previous to its consolidation) resemble very 
much the perforations in the azoic formation with this dif¬ 
ference ; the former are filled with the same material, sand; 
while the latter are usually filled with foreign material, or 
matter in a different state of crystallization. 
These perforations vary in size from a few inches to two or 
three feet in diameter. They are always filled with the same 
material as the rock in which they are found, but when the 
rock is removed the filling sometimes remains like a pillar of 
sandstone cast in a mould. A good specimen was found some 
time ago at Mineral Point, and is now in the possession of E. 
J. Cooper, Esq., of that place, whose good nature will lead 
him, we hope, to make a donation of it to the Academy of 
Sciences, where it will find its place among other specimens 
from the lead district. Such specimens are seldom met with, 
for it is only where the sand rock has obtained a certain de¬ 
gree of hardness that they can be found. Where it is more 
friable the impression only is found, reminding one of some 
ancient volcanic vents that are not only extinct, but filled 
with, and buried in their own ashes. 
Where the rock is sufficiently hard to retain its form, the 
filling separates easily from the mould, and the mould has the 
appearance of a channel or pipe through which water had been 
forced either from above downwards, or from below upward 
