Trail Section 4 - Falls Lake Trail Geologic Guide

 

Geologic Map Trail Section 4-7

Geologic information by Edward F. Stoddard (in Bold Text).

Mileage and Trail section descriptions from Mark Edelstein with updates from March – April 2011.

Trail Section 4:

9.5 – At end of guardrail, turn R to reenter woods.

9.9 – Midway through an area of young pine growth (Trail is marked by several carsonite posts), cross a wide roadbed.

10.0 – Enter more open woodlands.

10.2 – Note a former homesite, L. Soon enter a wildlife clearing, as the trail touches a wide roadbed and passes by the remains of a rusted car.

10.7 – Cross a small creek on a footbridge as you leave the wildlife clearing.

4-A:  Here there is a small outcrop on the trail, and a better, though moss-covered outcrop to the left along the creek.  The rock is a fairly typical fine-grained, quartz-rich mica schist of the Crabtree terrane.  Both varieties of mica, the light-colored muscovite and dark-colored biotite, are present.  The foliation dips steeply toward the west here.

10.9 – Return to lake views.

11.0 – Trail turns sharp L by a lake promontory.

4-B:  You will see a large pile of boulders to the left, and if you leave the trail and follow the short path to the right toward the lakeshore, there is more of the same.  This is more Crabtree quartz-mica schist, with layers of different composition locally giving a ribbed appearance on the weathered rock surfaces.  There are lots of quartz veins in the schist, and evidence that the rocks have been strongly deformed, with small folds, pinching and swelling of layers, and lineation present.  If you look carefully, you will find garnet crystals up to one cm in diameter.  There may also be some other metamorphic minerals such as staurolite, kyanite, or tourmaline. 
The Crabtree terrane is partly distinguished by the occurrence of schist with graphite, the soft black mineral that is a form of carbon, and from which pencil lead is made.  Some portions are extremely rich in graphite; in fact, former graphite mines which existed along a belt between here and west Raleigh have resulted in the name Lead Mine Road, a misnomer because it is not lead, but carbon!  If you see a dark gray or black example of schist, scratch it with a pocketknife and see if it produces a soft black powder that marks paper.

11.3 – Cross a narrow, old roadbed and soon enter an area of profuse laurel and holly.

4-C:  Through this stretch you will encounter numerous chunks of Crabtree schist, much of it with a bumpy or nubbly appearance.  The bumps are metamorphic porphyroblasts, crystals of garnet, staurolite, and/or kyanite that indicate the degree of metamorphism.

11.9 – At the end of a cove, cross a footbridge over a creek. You have now entered an area of state parklands (No hunting).

4-D:  Just downstream from the bridge, there is a low outcrop in the creek, and still further downstream, another one.  This rock is thinly layered quartz-rich schist of the Crabtree terrane, and its foliation has a fairly steep dip toward the east (Figure 4-D).

12.0 – Cross a creek bed on a low footbridge.

4-E:  As you go uphill, you will encounter a small rock ledge on the trail, with a better outcrop to the right.  This is an exposure of moderately to steeply dipping quartz-feldspar (felsic) gneiss within the Crabtree terrane.  This rock may have originated as a granitic intrusion.
Still further up the hill, there is more felsic gneiss, with crude disc-shaped grains of quartz and feldspar up to two cm.  The shapes of these flattened and stretched mineral aggregates attest to the strong deformation that this rock has experienced.

12.3 mi – Reach the Yorkshire Center, a NC Parks and Recreation facility.  Bayleaf Church Rd, L, dead ends here.

End of Trail Section 4

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