OUTLINES. 
12a 
sometimes considerable masses of magnetic and titanic iron. There is 
also one occurrence of serpentine in the upper part of Wake county. 
Besides the minerals just mentioned, iron pyrites, copper pyrites and 
specular iron are found occasionally, mostly in quartz veins, but also in 
the gneiss rock itself In one locality on the Cape Fear River, near the 
mouth of Buckhorn creek, there is a bed of red hematite nearly 40 
feet thick, together witli a slaty manganese garnet, interstratified with 
the gneiss, and the two minerals are combined in some parts of the bed 
into a mineral which differs little from knebelite. 
The second area of rocks which I have referred to the Laurentian, and 
the lower division of it, extends from the southern border of the State, 
where that is crossed by the Catawba river, in a northeast direction 
almost to the Virginia line at a point near the towm of Roxboro, in Per- 
son county, and re-appearing in a triangular tract 8 or 10 miles to the 
eastward, cresses the northern border about midway of Granville county. 
There is also another small area in the southern part of Orange including 
the University, which probably belongs here, although it is not repre- 
sented on the map. It will also be seen that there are several other 
small patches of the same color in different parts of the map, indicating 
other scattered outcrops of allied rocks. The main body is from 10 to 
thirty miles wide and has an area of about 3,000 square miles. 
The characteristic and prevalent rocks are syenyte, doleryte, green- 
stone, amphibolyte, granite, porphyry and trachyte. Dr. Mitchell says of 
these rocks : “ There is no well defined gneiss, mica slate, serpentine or 
limestone,” among them. “ Mica is rare, and in its stead there is chlo- 
rite, or hornblende, but even these are notin general well characterized 
and Dr. Emmons, “Trap-dykes are numerous at most places where the 
rock is exposed. At certain points they are so numerous that the rock 
is obscured. The dykes are not composed of one material, but consist of 
the common amphibolic trap, quartz, felspar and thin seams of epidote ; 
forming together a network of eruptive rocks. When they decompose, 
the hornblende trap appears in dark green stripes,- and many have as- 
sumed the structure of a laminated rock.” Mica is in fact rare through- 
out the series except at a few points where the rocks are granitic, and 
even in them the proportion of it is very small. The most common 
rock is of a kornblcndic character; and traps, trachytes, granulytes and. 
porphyries are confusedly and angularly wedged in among each other, 
with frequent veins of epidote crossing the felspathic species in every 
direction. 
The following analysis, by Dr. Genth, of one of these typical trachyte 
porphyries, the leopardite of Mecklenburg and other localities will show 
