APPENDIX—GEOLOGICAL SURVEY. 
471 
iron pyrites. I found a very handsome specimen of this kind 
there, some time ago, which is now, with the other specimens 
of the survey, in the cabinet of the Academy of Sciences, at 
Madison. 
To the north of the lead district, on the north side of the 
elevation of land running from Blue Mounds to Prairie du 
Chien, and in connection with the deposits of oxide of iron, I 
notice the same or very similar phenomena. Here, between 
the magnesian limestone and the Potsdam sandstone, we find, 
in places, beds of flinty hornstone which are occasionally broken 
up into fragments in the same way, and these fragments are 
cemented by the oxide of iron in a crystalline condition, rep¬ 
resenting exactly the form of the bars in the lead district, ex¬ 
cepting that the fragments are flint or hornstone instead of 
lime rock, as in the lead district. Specimens of this, also, may 
be seen at Madison. 
A little to the north of this, along the next elevation (the 
Baraboo hills) we find the same or very similar phenomena, 
only on a much larger scale, the result of exposure to more 
intense heat. Here we find not only bars but ridges of this 
altered rock. The ordinary reck is sandstone (Potsdam), but 
we find it gradually passing, sometimes into a fossiliferous 
sandstone, and from that into regular slate, at others into 
quartzite, and from that into the regular quartz rock. We find 
here, also, that beds of this quartzite from three to four hund¬ 
red feet thick have been broken up into fragments varying in 
size from a man’s head to a house, and thrown up in one mass 
around a center of force, as at Devil’s Lake. Nothing is more 
evident than that the phenomena in these three places are the 
results of the same general cause, modified only by local con¬ 
ditions. 
Now what is the change that this galena limestone in the 
lead district, and this sandstone at Devil’s lake have undergone? 
Let us see if we can ascertain by putting a piece of each 
under the'microscope. We will try the galena limestone first. 
In its normal condition, (that is its unchanged condition) it is 
made up of small grains like sand, cemented together with 
