80 ECONOMIC GEOLOGY. 
from iron pyrites. This cannot be said of the Hanover stone, which was used for the 
basement of Culver Hall. 
One thing should be said of this impurity in the Hanover rock. There is a building 
on Corey hill containing pieces of the pyrrhotite as large as beechnuts, and though the 
house has been standing nearly seventy years, there are scarcely any iron stains upon 
it. This species of pyrites sustains itself so well that oftentimes its presence need 
not be feared. A more remarkable instance of the ability of this pyrites to resist 
decomposition may be seen in the Francestown soapstone. I have examined many of 
the stoves manufactured from this stone, and noticed that bright particles of this 
pyrites were thickly sprinkled through it. I have also looked at pieces of this stea- 
tite that had been subjected to great heat for a long time without much change. It 
would appear, therefore, that this mineral may not be injurious to granites, as it seems 
to withstand successfully the vicissitudes of both heat and cold. 
Porphyritic Gneiss. This is: only employed locally. I have been greatly pleased 
with the appearance of curbs and foundation stones of this granite, as seen commonly 
at Lake Village and Meredith. The large rectangular white feldspar crystals render 
the stone attractive. There is a gray Scotch granite with these reddish-white crystals 
scattered through it, which is like our porphyritic gneiss. Those who desire a new 
variety may be pleased with this. The town of New Hampton abounds with hand- 
some ledges of this rock; but any of the areas thus designated upon the map will 
furnish to a careful search very attractive blocks. 
The White Mountain Granites. By these I mean the Conway, Albany, Chocorua, 
and sienite groups, of which whole mountains stand ready to be quarried, and thus be 
made serviceable to civilization. Of these, certain portions of the first are unsuitable 
for building purposes or monuments, because they disintegrate so readily. This has 
been explained (Part iv, p. 195) by the presence of innumerable pores in the feldspar 
which admit water charged with carbonic acid, and thus gradually impair the integrity 
of the stone.’ But all the Conway granite mountains are not of this character. The 
other varieties are also capable of furnishing peculiar grades of building stone, and 
perhaps the time is not far distant when their beauties will be discovered and utilized. 
Railroads now thread among the mountains, so that new quarries of stone can be easily 
transported to market. There are fine-grained varieties of the Conway species near 
the Portland & Ogdensburgh Railroad in the Notch, which are durable. A very hand- 
some stone of this sort has been used by Dr. S. A. Bemis for his dwelling, though 
more care might have been taken to secure a material free from pyrites. 
It was my intention to have presented statements respecting the 
points to be observed in selecting a good granite for quarrying, the appli- 
cation of microscopic study, and a comparison of our stone with the 
Scotch, Massachusetts, and other kinds of building material, particularly 
with reference to strength and ability to resist decomposition. The 
