70 
AMElilCAN GEOLOGY. 
of construction, dams, culverts, viaducts, &c. It extends many 
miles in length. Granites only slightly elevated above the 
general level of the country form a low and rather continuous 
ridge, extending through Virginia, North and South Carolina. 
This ridge forms the first waterfall of the Rappahannock, 
James, Roanoke, Tau, Neuse, and Cape Fear rivers. It is 
often a variety which may be called a gneiseoid granite. 
Granite underlies in part the counties of Guilford, Davidson, 
Rowan, Mecklenburg, and Lincoln. The belt extends south 
into South Carolina. But a compound of feldspar and quartz is 
one of the most common rocks at the base of the Blue ridge. 
Granite is by no means a common rock in the higher parts of 
the Hoosick mountain and the Blue ridge. The most common 
rocks of these high ranges are mica and talcose slates, hornblende 
and gneiss. 
On the west side of the Blue ridge granite is equally scarce, 
and when it occurs it is mostly in veins, and consists of quartz 
and feldspar, a rock which is sometimes extensive. It decom¬ 
poses, and forms a great abundance of white clay. About four 
miles west of Ashville, Buncombe county, a handsome granite 
suitable for architecture crops out and crosses the road; but 
most of the rocks skirting the French Broad river are gneiss 
and mica slate. Granite occurs four miles east of the Warm 
springs: it rises in a dome-shaped mass, and supports quartz 
and slate rocks, the lower members of the Taconic system. 
South*westward and westward from the Warm springs all the 
rocks to the Mississippi river belong to the sedimentary class. 
Granites of the same kind and character appear in Macon and 
Cherokee counties, and from thence they extend into Georgia. 
They never form large and important masses among the rocks. 
To the south-west and west of the Mississippi granite occurs, 
and forms in part a low range of mountains, which have been 
called the Ozark mountains. Their tops rise like islands in the 
midst of cretaceous seas. In the Thousand isles of the St. Law¬ 
rence, and so onward to the west in the Lawrentine chain, 
granites and sienites are far more common than in the Appa- 
