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WISCONSIN STATE AGRICULTURAL SOCIETY. 
mortar. When this cement is dissolved, as in the case where 
it is exposed long to atmospheric agencies, these little grains 
fall apart from each other and look very much like sand. 
When we take one of these little grains alone on the slide, and 
put on a higher power, we see it is a little crystal of calcare¬ 
ous spar, or what the miners call tiff; its little face will 
sparkle in the light, and its angles lie almost as distinct as a 
piece of tiff that we hold in our hands. 
But let us try now a piece of the bar-rock. We can see 
the same little crystals, but they are blended into one solid 
mass, as though they had been partially melted; they are no 
longer little grains or crystals, but a solid mass of crystals form¬ 
ing a rock of high crystalline texture. Now, what is true of 
this galena limestone and the bar-rock, is true also of the sand¬ 
stone and. the quartzite, except that in one the grains or crys¬ 
tals are lime or calcareous spar, in the other silica or quartz. 
Now if we ask scientific men what such rocks are called 
when altered in this way, they will tell us metamorphie rocks. 
If we ask them what it is that has produced this change in 
sedimentary rocks, that they now assume this crystalline char¬ 
acter, they tell us that it is either produced by igneous rocks 
thrown up into their midst, or by heat. If we ask under what 
form this heat was presented, they answer, “ intensely heated 
water under great pressureeither is sufficient to produce it. 
Here we again meet with plutonic and hydro-plutonic forces 
in their endless round of rock and mineral formation and trans¬ 
formation ; we meet them, and shall continue to meet them at 
every turn in the mineral strata, No one will be astonished 
if we state that quartzite is metamorphie sandstone; but if I 
should state that this bar-rock in the lead district is metamor- 
phic limestone, the statement would be received with surprise, 
and with a certain degree of distrust. And yet one is just as 
much a metamorphie rock as the other; just as much the re¬ 
sult of transformation by heat as the other. It is in these little 
details of the phenomena with which the lead district abounds 
that we find the evidences of the action of the physical forces 
from below. 
