122 
GEOLOGY OF NORTH CAROLINA. 
eastern margin, being covered up by Quaternary sands and gravels. This 
belt consists of light colored and grey gneisses, which occasionally pass 
into granite, but more frequently into felspathic, quartzose (and rarely 
hornblendic) schists. In some localities the mica is entirely wanting 
and then the rock is either a dull-reddish, brownish, or whitish massive 
felspathic rock, trachyte, euryte, felspar porphyry, &c. 
The rocks of this belt are usually quite fine grained. The predominant 
element in their composition is felspar, although quartz is abundant; the 
proportion of mica, which is usually biotite, is very small. The strike 
of the strata is generally between 20° and 30° east of north, and the dip 
east, usually at a high angle, from 65° to 80°, and down to 40° and 45°. 
The rocks are much disturbed and very irregular in position. 
The following analysis will serve to give a general ieda of the charac- 
ter and chemical composition of the rocks of this belt, the sample being 
selected from the Raleigh quarries and as nearly a typical specimen as 
possible. 
Silica, 69. 2S 
Alumina, 17.44 
Sesquioxide of iron, 1.08 
Protoxide of iron, 1.22 
Lime, 2.20 
Magnesia, 0.27 
Potassa, 2.76 
Soda, 3.64 
Manganese oxide, .16 
At one point on the Cape Fear, the felspar of the gneiss is partly re- 
placed by calc spar. 
There are a few points some distance to the eastward of the general 
boundary of this belt, where there are local and limited outcrops of gneiss 
and granite, appearing through the general covering of sand, most of 
which are indicated on the map, as at Weldon, Rocky Mount and two 
other points in Edgecombe, and one in Wilson. The granite for the 
United States post-office, in Raleigh, is obtained from Edgecombe. It is 
of light grey color, and shows no gtieissic or foliated structure, being un- 
distinguishable from true granite. The rock at two other of these lo- 
calities is of the same general description, but much coarser grained, and 
is likewise used for building purposes. Ledges of coarse syenite and dio- 
rite dikes occur occasionally in this tract, and with the former grains and 
