Glennstone Notes for Signage

Concept 1 for Sign: What makes Glennstone Preserve special?

I. GEOLOGY:

DIABASE GLADES (Jurassic Diabase in Triassic Basin, Iredell soils)

Following excerpt from A GEOLOGIC ADVENTURE ALONG THE ENO RIVER-Information Circular 35 by NC Geologic Survey (p.25):

DIKES AND SILLS INTRUDE THE TRIASSIC BASIN AND INTO CAROLINA TERRANE ROCKS

MAFIC magma from deep in the earth welled up through fractures in the crust at the beginning of the Jurassic period (approximately 195-205 million years ago). This magma intruded the sediments of the Triassic basin and surrounding crystalline rocks of the Carolina terrane. At the same time, to the east of the Durham Triassic basin, the main rift separating the North American and African continents was growing, causing the continents to slowly move away from each other. Mafic magma also welled up through the main rift zone, known as the mid-Atlantic ridge, and provided the raw material for the expanding ocean basin. In the Durham Triassic basin, the magma solidified into rock known as diabase. Diabase is a mafic rock with a composition similar to ocean floor basalts.

In the Durham Triassic basin, diabase is more resistant than surrounding sandstones and siltstones it intrudes and often forms resistant ridges in the Durham area. Penny’s Bend on the Eno River is underlain by diabase. Diabase is composed of minerals that contain abundant iron and magnesium in comparison to the Triassic sediments. Because of the abundance of iron and magnesium, unique plant communities sometimes develop on top of areas underlain by diabase (e.g. The Diabase Glades).

My note: I included this because it so well explains, with the aid of a geological map that is included in this circular, diabase glades. (You can even see sills on Glen Road near Club Blvd. on this map!) Of course, it is way too complex for interpretive sign but helpful perhaps when writing concepts, geological timeline or maps.

2. PLANT COMMUNITIES:

A. TWO TYPES OF UNUSUAL (for Piedmont) PLANT COMMUNITIES: PRAIRIE/MEADOW AND POST OAK FOREST. (we need to check the Natural Heritage Program's description of plant communities to see which ones fit Glennstone)

B. MORE DIVERSITY PLANTS WITHIN COMMUNITIES, due to north-facing slope, lack of plowing, and presence of diabase soils.

3. GLENNS HOMESITE:

1. FIRST(?) COLONIAL SETTLEMENT (Old homesite ruins may be nearby)
2. LARGE PIECE OF NORTH SLOPING LAND RELATIVELEY UNDISTURBED (logged in last decades of 1900’s, but not plowed or developed). This affected swift return to forest saplings. Other factors can affect and interrupt successional stages as well….

4. PROXIMITY TO ELLERBE CREEK AND Alluvial corridor of MATURE FOREST extending down to and around Falls Lake. Provides intact corridor for wildlife.

5. PROXIMITY TO HERON ROOKERY.

6. Borders Glenn Cemetery, with headstones dating back to 1700s.

Concept 2 for Sign

The second potential concept for the interpretive sign would focus on succession, but not present succession as an inevitable shift from herbaceous to mature forest, but instead use a double arrow (a two-way street, essentially) between prairie and forest, with natural forces such as fire, along with anthropogenic forces like logging and mowing, pushing the plant community towards prairie, while successional forces push towards trees.

We can point out that some areas are resisting tree growth on their own--most likely due to stronger diabase characteristics in the soil that discourage tree growth.