Trail Section 2 - Falls Lake Trail Geologic Guide


Geologic Map Trail Section 1-3

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 2

3.7 – At end of guardrail, turn R to head back into the woods.

Between the end of Section 1 and the beginning of Section 2, you have crossed the Falls Lake thrust fault and are now in the Falls Lake terrane.  This rock unit is distinguished by the occurrence of ultramafic rocks; these are a group of metamorphosed igneous rocks that contain no quartz or feldspar.  In actuality, the Falls Lake terrane is at least 80% schist, but it also contains hundreds of bodies of ultramafic rocks, ranging from a few inches to over a mile across.  Because the enclosing schist is more easily weathered, the ultramafic rock types are disproportionately visible along the trail.

2-A:     Along the first stretch of this trail, one encounters large blocks and outcrops of dark greenish rocks containing the minerals actinolite and chlorite (Figure 2-A).  Chlorite is a flaky mineral, like mica only dark green, while actinolite is rectangular or needle-shaped.  If you look closely, you may see small actinolite crystals in a radiating "starburst" arrangement.  These metamorphosed ultramafic rocks show foliation, which may take the form of layers, banding, or flakiness, like the pages of a magazine.  The banded actinolite rock reappears several times along this stretch; it follows the trail for about the first mile.

4.1 – Skirting a cove, cross a small footbridge.
4.3 – Reach lake views, which are plentiful along this area.

2-B:    In addition to the actinolite-chlorite rock, you may see a small block of soapstone, another ultramafic variety.  Soapstone is composed of the mineral talc, soft enough to be scratched with a fingernail.  If you suspect soapstone, scratch the rock with a hard object such as a pocketknife or car key.  If it scratches easily, then rub your finger lightly across the area you have scratched.  If it feels like baby powder, you’ll know why!

2-C:    There are also some piles of chunks of quartz through here.  In some you may see crude milky white crystals (Figure 2-C).

2-D:    Here, a low ridge crosses the trail.  You will see that it is held up by more fo the actinolite-chlorite rocks.  If you examine some of them closely, you may see small black crystals of magnetite.  The shape of these crystals is characteristic; it is an octahedron - an eight-sided form with triangular sides.

4.9 – Cross a footbridge above a small creek. In times of high water a small cascade is visible to the L.

2-E:     Here there is a very nice outcrop of light-colored, fine-grained schist, consisting of feldspar, quartz and mica.  There are also a couple of dikes (cross-cutting intrusions) of pegmatite with large mica flakes.

5.0 – Cross an old roadbed. To the R is a path to a former homesite on the lakeshore.
5.2 – Pass a pond, L.

2-F:     While walking across the dam, look to the right and you will see a huge rock outcrop.  If you care to explore a bit (Beware of the poison ivy!), you will see that this is schist, with mica, garnet and kyanite as well.  You may also see thin seams of quartz cutting across the foliation of the schist.
As you continue on the trail, you'll encounter some similar schist, as well as loose pieces of quartz, some containing kyanite too.

5.3 – Turn L to stay on the trail (R leads to the lake).

2-G:    Here you may encounter the rootball of an uprooted tree, with pieces of quartz and also schist with kyanite.
2-H:    Here, just before the small creek, you will come upon another outcrop of the actinolite-chlorite rock.  Remember, the schist that you have seen represents the bulk of the Falls Lake terrane (the matrix).  The ultramafic rocks occur as pods completely surrounded by schist, like the chips in chocolate chip ice cream.

5.6 – On stepping stones, cross a small creek.
5.9 – Cross a low footbridge over a dry creekbed.

2-I:      On the hill you will see lots of large chunks or boulders of milky quartz.  Geologists call this “bull quartz.”

6.2 – Exit the woods to Red Fox Run, a private, gravel road.
6.3 mi – Junction with Possum Track Rd, by a dead end, and cross this to continue on the Falls Lake Trail.

End of Trail Section 2

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