302 
GEOLOGY OF NORTH CAROLINA. 
the hardness of the rock; they do not seem to have been able to pene- 
trate the unweathered and more solid portions of the ledges in any case, 
a circumstance which shows the inferiority of their tools. 
As to the uses to which this mineral is put, the principal one seems to 
be to furnish windows for parlor stoves. But it is also manufactured into 
lamp-chimneys and shades, and it is also latterly used, to some extent, 
already, as among the ancients, for purposes of personal ornaments of 
women — another illustration of the periodicity of fashions. The me- 
chanical uses are multiplying, so that ere long the demand will no doubt 
overtake the supply, and when that happens, a large field of profitable 
industry will be open to many counties of the State. 
Building Stonf.s. 
Prom what has been said under the head of general geology, it will be 
apparent that there exists the greatest abundance of material for archi- 
tectural and engineering uses, over a large part of the state. Granite 
and gneiss are among the commonest rocks throughout its whole length, 
except in the coastward region, where it is overlaid by the Tertiary and 
Cretaceous beds. And the sandstones of the Triassic, red and gray, as 
well as those of the Huronian, are available over considerable areas ; 
while the shell-limestones of the Eocene furnish a very fair building ma- 
terial to the sandy and alluvial coast region ; and the crystalline limestones 
and marbles of the west supply an ornamental building stone of great 
variety and beauty. 
Granites . — The capitol is built of the light colored gray gneiss which 
is so abundant in the Laurentian formation of the 6tate, and in the Peni- 
tentiary, which is in process of building, the same material is used. An 
analysis by Mr. Hanna shows the composition of this rock. It is as fol- 
lows : 
Silica, 69.28 
Alumina, 17.44: 
Sesquioxide of Iron, 1.08 
Protoxide of Iron,. 1.22 
Manganese Oxide, , 0.16 
Lime, 2.30 
Magnesia, 0.27 
Potassa, 2.76 
Soda, 6.64 
