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 Moimtaiti 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 liave presented statements respecting the 

 points to be observed in selecting a good granite for quarrying, the appH- 

 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 



