OF GNEISS. 27 
being disposed in concentric layers. Granite is often traversed 
by veins. 
A great diversity of aspect is exhibited by different granites, 
even where the ingredients are the same, depending upon the 
color of the ingredients, the greater or less perfection of their 
crystallization, and the size of the grains. Some undergo decom- 
position rapidly, and to a great depth, as in Caswell. Good mill 
seats are rare where the rocks have this character. Other granites 
remain unchanged, though exposed to the action of the elements 
for a very long time. The flat rocks of Franklin, Rowan, and 
Stokes, furnish a striking illustration. Whilst the crust of the 
globe about them has been converted into soil, they have remained 
apparently unchanged from the time of their formation to the 
present day. They have a vegetation of their own. Plants are 
found growing upon them that are not met with elsewhere for 
many miles, and some that are altogether peculiar to them. 
Granite is a common and widely distributed rock. It occurs 
in almost every great range of mountains, of which it generally 
forms the central and highest parts, having the more recent 
formations resting upon it. It occupies a lower level in America 
than on the eastern continent. With the exception of Mont- 
gomery, where, if it exists at all, it is recent and imperfectly 
characterized, there is no one of the upper counties of North 
Carolina, that does not contain more or less of it. Werner sup- 
posed all the granite rocks to have been formed contempora- 
neously, and to be therefore of the same age. It is quite certain 
that this is not true. The granite of the eastern and western 
counties, Warren, Franklin, Wake, Lincoln, Rutherford, Burke, 
Wilkes and Surrey, appears to be older than that occupying a 
part of the intervening space in Granville, Orange, Caswell, 
Guilford, Davidson, Rowan, Cabarrus and Mecklenburg. 
The minerals that are found imbedded in granite are numerous, 
but in general not valuable. It is not rich in the metallic ores. 
The tin mines of Cornwall and of Saxony, are in granite, and it 
also embraces beds of iron ore. This rock is indeed so widely 
distributed over the surface of the globe, that it was to be ex- 
pected that on searching the whole world over, mines of most 
of the metallic ores would be found in it; but where they 
exist! they are generally poor, and will not repay the expense 
and labor of working them. 
OF GNEISS. 
16. The second rock in the Wernerian arrangement is gneiss, 
which is said to rest upon and cover the granite, and to be 
itself covered by the other strata. The minerals which enter 
into its composition are the same with those that form granite, 
but the proportions are different and they are differently arranged. 
Proper gneiss is constituted of quartz, feldspar, and mica. The 
mica is frequently more abundant than in granite, and is so dis- 
