Pilot Mountain Field Trip. CNCMC Meeting, Feb 2013

Joseph Mack

jmack (at) wm7d (dot) net
CNCMC

10 Nov 2013


Table of Contents

1. Sources
2. Geological Introduction
3. Non Geological Introduction
4. Where is Pilot Mountain?
5. Sauratown Mountains
6. Pilot Mtn: a Quartzite Cap
7. Monadnocks
8. Beaches
9. Age of Pilot Mtn
10. Laurentia, Iapetus Ocean
11. Windows and Crashing Rocks
12. Peneplain, Pediment
13. Sauratown Window
14. Schist
15. Field Trip
15.1. Grassy Creek, CGS Stop 12, 36.948N, 80.455W
15.2. Diamictite, Pilot Mtn road inside park, CGS Stop 14, 30.345N, 80.473W, el 1643'
15.3. stratigraphy of Big Knob
15.4. Pilot Mtn Big Pinnacle, CGS Stop 13
15.5. Pilot Mtn Big Pinnacle, Ledge Spring Trail, side along the bottom of the cliffs
15.6. Pilot Mtn Big Pinnacle, Ledge Spring Trail, side on top of cliffs
16. Conclusion
17. Questions

Abstract

General geology of Pilot Mountain and the Sauratown Window. Preparation for a field trip to the area.

1. Sources

Most of the information here came from the field notes from the Carolinas Geological Society 1988 meeting "Structure of the Sauratown Mountain Window, North Carolina" [1] . Most of the rest, including images came from webpages. I started with the book "Exploring the Geology of the Carolinas", by Stewart and Roberson [2], but had trouble building on their model of the geology at the Park. I didn't have time to look into "The Geology of the Carolinas" [3] .

I would like to thank Phil Bradley of NCGS for suggestions and time spent answering questions.

not for presentation

I'm not a geologist. This is my best attempt to understand the geology of Pilot Mtn, in preparation for a field trip I planned for CNCMC. We're just a club of people trying to educate ourselves. Please don't regard me as an educated or primary source on anything.

The style, terms and names used in the popular press on one hand and the professionsl books on the other, are so different, that you have to reconcile the two sets of information before you see that they're talking about the same thing. Phil Bradley, of the NCGS, says that the CGS field notes are written in CGS-speak and even a geologist has to read them 5 times to understand them.

Photos here are attributed to their original source. Photos by me are (C) Joseph Mack and are released under GPLv3 license.

2. Geological Introduction

Figure 1. Pilot Mountain from Rte 52

Pilot Mountain: source http://www.wvexp.com/index.php/Appalachian_Mountains
Pilot Mountain: source http://www.wvexp.com/index.php/Appalachian_Mountains

Pilot Mountain rises 1400' above the surrounding flat Piedmont. The last 200' is an erosion resistant Cambrian (540-460Mya) quartzite cap, called "The Knob" or "Big Pinnacle". There are actually two peaks, "Big Pinnacle" and the much smaller "Little Pinnacle" (on the left in this photo). Underneath is four layers of thrust sheets of late Proterozoic (1.2Gys) schist and gneiss. which were pushed under the quartzite in the Alleghenian orogeny about 300Mya.

Looking at this photo, I identified the knobs as the quartzite and the rounder hills underneath as the schist. It was only about 10days ago, on re-reading the CGS 1988 field trip notes for Stop 12 (p78), that I realised that there might be more quartzite than just the knobs. In fact the whole view here is quartzite, but you can't tell from this photo. The basement rock starts outside the park. What can you tell about the season this photo was taken [4] ? Look at the left hand sloping ridge in the photo above; it's green hiding everything beneath. (Part of the field trip will be to walk along this ridge, using the Ledge Spring trail.)

not for presentation

This photo was taken from an overpass on Rte 52. On my recent pre-field trip reccy, I took photos from under this overpass, without thinking to walk up on top of it.

Here's my photo, taken in winter. Look at the Ledge Spring trail area again.

Figure 2. Pilot Mountain from Rte 52 in winter

Pilot Mountain in winter from Rte 52. source Joseph Mack (C) 2013
Pilot Mountain in winter from Rte 52. source Joseph Mack (C) 2013

Here you can clearly see the quartzite blocks sloping down to the west. In fact all the strata of Pilot Mtn slope down over the dome of the mountain.

Pilot Mtn, Hanging Rock and the Sauratown Mountains are part of a larger, recently (1970-80s) recognised structure, the Sauratown Window which contains the Sauratown anticline [5] .

3. Non Geological Introduction

As part of the field trip, we will join the ranger guided public hike on the Jomeokee trail, around Big Pinnacle, a total distance of about 1.5miles. You are no longer allowed on top of Big Pinnacle, so the walk will be relatively unadventurous.

An early european name for Pilot Mountain was Mt Ararat, after the traditional landing place, in Turkey, of Noah. There is a nearby town, Ararat. The name of another nearby town, Mt Airy, is a contraction of Mt Ararat [6] . I can't imagine anyone here spending their spare time watching TV, but if you had done such a thing, then it may be of interest to know that Andy Griffith's hometown is Mt. Airy, which was the model for Mayberry [7] . The fictional Mt. Pilot in the Andy Griffith Show is named after Pilot Mountain.

The local native americans were the Saura [8] . The tribe is now extinct and little is known about them. We don't even know their language. The natives cleared the valley bottoms, with fire and using spring floods, to allow planting and to encourage grass for game, such as bison and deer. The valley floor ecology was quite different then to what we see now. DeSoto went through the area in the early 1500's, commenting on the large numbers of natives. When Europeans arrived in the 1700's, the area was filled with deserted villages, presumably the result of diseases introduced by de Soto [9] . The Saura were living in the Piedmont area near the Sauratown Mountains, east of Pilot Mountain and north of the Yadkin River. This may not have been their original location. At the time the Saura were involved in war with other native american tribes and were used by the Europeans in wars against other native americans, something they can't have been too happy about, as it exposed their villages to attack by native american tribes [10] .

The arriving europeans were settlers. They did not come from the east as you might expect, but instead came from Pennsylvannia, down the Blue Ridge, an arduous journey, often requiring disassembly of wagons, to cross obstacles. The settlers were fleeing religious persecution at the hands of the people who themselves had left Europe to flee religious persecution. The land the settlers occupied, was sold to them by the govenor of NC. It was the land cleared by the no-longer present natives. [11]

The Saura name for Pilot Mountain was Jomeokee, meaning "Great Guide". One of the trails we will be walking on is called the Jomeokee trail. Pilot Mtn is visible from the Blue Ridge (at least on a clear day) and alerted the settlers that they were arriving in NC. Apparently it was used for navigation by the natives too. On my recent trip, I couldn't see Pilot Mtn till I was almost at it, even though I was looking through trees in winter from the flat Piedmont. Once in the park, you don't see Pilot Mtn from the road, till you're at the parking lot up top. You can see it in one section on the way down. I can't imagine how you'd ever see Pilot Mtn in summer from anywhere. Maybe it was different back in the days when the valley floors were cleared.

The relief in the Piedmont is small (one of the problems in finding interesting field trips), but the greater elevation of Pilot Mtn, rising above the Piedmont, provides a colder microclimate [12] .

  • It has rhododendrons, mountain laurel, pitch pine and table mountain pine, all remants from the last ice age.
  • Ravens, which are normally found further west (in the Blue Ridge Mountains), nest here, one of the few sites in the Piedmont where they do so.

    From a google search, ravens nest at Grandfather Mountain [13] . Ravens also nest at Chimney Rock State Park [14] 25miles SE of Asheville, NC, but I don't think that's Piedmont anymore. (As you probably can guess, ravens don't nest at Raven Rock State Park.) Although there isn't a trail to the top of The Knob, 40yrs ago there used to be ladder to scale the cliff. Maybe it was part of the ranger guided hikes back then, but it's been removed supposedly to give the nesting ravens some peace [15] . Maybe they could just lock the ladder in raven nesting season. Rockclimbers are allowed on the top [16], because, as we all know, nesting ravens are not at all disturbed by rockclimbers, the only humans they seem to accept.

4. Where is Pilot Mountain?

Here's where we're going. Google Maps says it's 108miles and 1hr 45mins from Chapel Hill.

Figure 3. Pilot Mountain location

Pilot Mountain location: source google maps
Pilot Mountain location: source google maps

Note
exclude from presentation.

Some webpages describe Pilot Mountain as being part of the Appalachians. Some describe it as part of the Piedmont (rather than the Blue Ridge Mountains). Some describe Pilot Mountain as an outlier to the Appalachians. I have no idea myself. (Is the Piedmont part of the Appalachians?) Let's look at some maps.

Figure 4. Relief Map of NC by County

Pilot Mountain: source http://upload.wikimedia.org/wikipedia/commons/thumb/6/6a/USA_North_Carolina_relief_location_map.jpg/800px-USA_North_Carolina_relief_location_map.jpg
Relief Map of NC by County: source http://upload.wikimedia.org/wikipedia/commons/thumb/6/6a/USA_North_Carolina_relief_location_map.jpg/800px-USA_North_Carolina_relief_location_map.jpg

The Blue Ridge Mts are in the brown area running NE-SW on the left of the map.

If you look in this unlabelled map, in the 4th county from the top left of NC (the 2nd squarish light green county), in the center of the county is a bump. This is Hanging Rock (and the State Park). Looking SW of Hanging Rock in the same county is a another bump, the Sauratown Mountains, named after the Saura. In the county to the left (the first light green county starting at the top left), Pilot Mtn is the bump in the bottom right, just as the Yadkin River turns from going east to going south. Pilot Mountain is not in the Blue Ridge, it's on the flatland and is not a particularly large feature.

Here's another physical map, with shadowing, which shows the Sauratown arc more clearly.

Figure 5. Relief Map of NC by County

http://geology.com/state-map/maps/north-carolina-physical-map.gif
source http://geology.com/state-map/maps/north-carolina-physical-map.gif

Here's a contoured elevation map. This does show the arc starting with Hanging Rock in the NE, through the Sauratown Mountains to Pilot Mtn in the SW.

Figure 6. Contoured Elevation Map of NC

Contoured Elevation Map of NC: source http://www.geology.com/
Contoured Elevation Map of NC: source http://geology.com/

Here's the tranditional zoning of NC into environmental provinces.

Figure 7. The Four Environmental Provinces of NC

The Four Environmental Provinces of NC: source http://www.learnnc.org/lp/editions/cede_lonemts/?ref=search
The Four Environmental Provinces of NC: source http://www.learnnc.org/lp/editions/cede_lonemts/?ref=search

The counties identified in the previous map are the first and 2nd pink squares in the top left of the map, i.e. in the Piedmont Environmental Province.

The environmental province is what's on the surface. Remembering that the surface is largely determined by what's underneath, what's the geological view of the state?

Figure 8. NC Geology

North Carolina Geology: source http://www.geology.enr.state.nc.us/usgs/rocsbaby.gif
North Carolina Geology: source http://www.geology.enr.state.nc.us/usgs/rocsbaby.gif

This puts Pilot Mtn in the "Inner Piedmont", which doesn't tell us a whole lot about the geology. However the Inner Piedmont Belt is the most intensely deformed and metamorphosed segment of the Piedmont [17] . These rocks are about 750 to 500 million years old.

Here's a close up view of the inner piedmont.

Figure 9. Inner Piedmont Belt, Chauga Belt, Smith River Allochthon, and Sauratown Mountains Anticlinorium

Inner Piedmont Belt, Chauga Belt, Smith River Allochthon, and Sauratown Mountains Anticlinorium source http://www.geology.enr.state.nc.us/usgs/innerpie.htm
Inner Piedmont Belt, Chauga Belt, Smith River Allochthon, and Sauratown Mountains Anticlinorium

We're interested in CZq. What is it? This more detailed geological map shows us. The Sauratown Mountains are the 8th (brown) entry in the left column.

Figure 10. Generalised Geological Map of NC

Generalised Geological Map of North Carolina: source http://www.jeffreycreid.com/MEA110.html  http://www.jeffreycreid.com/NC_generalized_geology_map.jpg
Generalised Geological Map of North Carolina: source http://www.jeffreycreid.com/MEA110.html http://www.jeffreycreid.com/NC_generalized_geology_map.jpg

By matching colours (the brown, rgb=190,135,50), we find that the Sauratown Moutains (and Hanging Rock and Pilot Mtn) are part of the Sauratown anticline.

What is an anticline [18] ?

  • anticline: In structural geology, an anticline is a fold that is convex up and has its oldest beds at its core.
  • antiform: The term is not to be confused with antiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships between various strata are unknown, the term antiform should be used.

This geological map above came from Jeffrey Reid's site, which had a link to the list of highest points in each NC county [19] . Since we're all experts in this sort of thing, what's the highest point in Orange County [20] ? There is a guided geological tour of this place, you get to check out the pyrophyllite mine and take home souvenirs.

5. Sauratown Mountains

We've arrived at our first piece of geology, the anticline with Hanging Rock in the NE, the Sauratown Mountains in the middle and Pilot Mtn in the SW.

Here's the Google Maps view of the Sauratown Mountains. On the left is Pilot Mtn. The next feature to the right is the Sauratown Mountains, which is all privately owned. The next feature to the right (in the middle of the map) is Hanging Rock State Park, which covers all of that group of mountains, including the outlier to the SE (which is part of the park, but unnamed in Google Maps and is possibly Flat Shoals Mountain). The isolated mountain to the N running EW is Brown Mountain, which is all privately owned.

Figure 11. Pilot Mountain Google Maps

Pilot Mountain from Google Maps
Pilot Mountain from Google Maps

Being an anticline the strata in the middle are at a higher elevation than at the ends. I had assumed that the anticline was a gentle rise in the SW-NE direction, with the lowest points at the SW and NE ends. In fact the height of the 3 sets of mountains is the same. The anticline runs at right angles to the line of the mountains and is the result of the thrust faulting which built the mountains. It has a small radius NW-SE across the spine of the range.

The Sauratown Mountains have more in common geologically with the rocks in the western Mountains (e.g. similar aged rocks are overlain by a well known quartzite/sandstone unit, the Chilhowee Group, in Tennessee, the Chilhowee Group quartzite exposed at the Grandfather Mountain window, and the Unaka belt in the western Blue ridge [21]) than in neighbouring terranes [22] .

From the map, if you're at Pilot Mtn, by looking at an azimuth of 70, you'll look across the flat cap of the Sauratown Mountains.

Here's a photo of the Sauratown Mountains from LearnNC.

Figure 12. Sauratown Mountains

Sauratown Mountains: source http://www.learnnc.org/lp/editions/cede_lonemts/609
Sauratown Mountains: source http://www.learnnc.org/lp/editions/cede_lonemts/609

Although the legend in the original website doesn't tell you what you're looking at, I surmise that we are standing on Little Pinnacle and have

  • Pilot Mtn on the right in the foreground
  • Sauratown Mountains on the left in the midground, which you can identify by the radio tower,
  • and the large Hanging Rock State Park in the middle in the background.

Not for presentation

We need to know a bit about dip and strike to navigate our way around the park. In the photo above, you're looking from Pilot Mtn at the W end of the Sauratown Mountains across the spine of the range. From the map, we know this direction has an azimuth of 70. The strata in the Sauratown Mountain cap slopes down to the left (N).

  • The strike of a plane is the line of intersection of the plane with the horizontal. The Sauratown Mountains intersect with the horizontal plane in a nearly E-W direction; it's actually 70.
  • The dip of a plane is the angle the plane makes with the horizontal, in the direction at right angles to the strike (which will be in the direction of the steepest descent). An E-W striking plane can have the N or S end of the plane, up or down. In the Sauratown Mountains, the plane dips 20 in an approximately N direction (actually 340). The dip then is 20N.

The strike and dip then are 70/20N.

Here's a closer photo of the Sauratown Mountains from wikipedia [23] showing the tilted strata of the quartzite cap. There is no information on where it was shot from or in which direction we're looking. Other than that, it's an informative photo. From the location of the radio tower(s) and the dip being about 20 (the same as seen from Pilot Mtn), I expect the photo is taken looking from the NE, back towards Pilot Mtn.

Figure 13. Sauratown Mountains tilted strata

Sauratown Mountains: source http://en.wikipedia.org/wiki/Sauratown_Mountains
Sauratown Mountains: source http://en.wikipedia.org/wiki/Sauratown_Mountains

Not for presentation

There are two parks at the ends of the Sauratown Mountains; Pilot Mtn and Hanging Rock. As the crow flies, the distance between the two park HQs is about 6miles. Crows can walk there and back in a couple of hours. For the rest of us, a 20mile bridle path, running through the Sauratown Mtns, connects the two parks, I expect someone has done a bit of work to arrange the various rights of way. Here's the write-up from wikipedia (using the correct spelling of "bridle") [24]

Sauratown Trail is a hiking and bridle trail in Stokes and Surry counties, North Carolina, which crosses the Sauratown Mountains and interconnects Pilot Mountain State Park and Hanging Rock State Park. It is the only bridle trail which goes between two NC State Parks. The trail is located primarily on leased, privately owned lands, and it is the longest publicly open trail on private lands in the state. The trail consists of a main trail of 22.2 miles (35.7 km) and two spur loops each about 6 miles (9.7 km) around. Altogether, the Sauratown Trail and its spurs total over 30 miles (48 km) of trail. The trail was dedicated by the Sauratown Trail Committee in October 1979. Since 2002, most of the main trail has been designated a part of the Mountains-to-Sea Trail.

The distance between the two park HQs, for us non-crows, is 22miles [25] requiring a bicycle to do the trip in a reasonable time. According to the Friends of the Mountain to Sea Trail [26] , you should have no expectation that you can complete the 22 mile trip. Several sections of the trail are being worked on, re-routed or closed. When you arrive at a closed part, you pull out your laptop and go to the Sauratowns Trails announcements webpage, a webpage that doesn't exist. (This is due to the ephemeral nature of the internet and confirms the futility of having links on webpages.) The trail is closed in deer hunting season, as deer hunters can't tell the difference between a deer and a human riding a bicycle.

Figure 14. Sauratown Trail Map

Sauratown Trail Association: source converted from pdf map at http://www.sauratowntrails.org/
Sauratown Trail Association: source converted from pdf map at http://www.sauratowntrails.org

The Sauratown Mountain anticline has 3 high areas that haven't yet been eroded down [27] .

  • Pilot Mountain 2,421 feet (738 m)
  • Sauratown Mountain 2,441 feet (744 m) (no public access. a gated privately owned road leads to a communications tower)
  • Moore's Knob (Hanging Rock State Park) 2,579 feet (786 m)

Here's these three peaks, in a photo looking from the NE taken by cyclists, doing a 200km run. L-to-R: Hanging Rock State Park, Sauratown Mountains, Pilot Mtn

Figure 15. Sauratown Mts, 3 peaks from NE

Sauratown Peaks from NE: source http://ncrandonneur.blogspot.com/2010_11_01_archive.html
Sauratown Peaks from NE: source http://ncrandonneur.blogspot.com/2010_11_01_archive.html

6. Pilot Mtn: a Quartzite Cap

Here is Pilot Mtn from the south. The top layer of the anticline has been eroded away in all but a few places. It's quartzite and is the distinctive feature of Pilot Mtn. Both the main peak (Big Pinnacle) and Little Pinnacle to its west (left in this photo) are quartzite. The quartzite layers are horizontal in this view, because we're looking at right angles to the strike line.

Figure 16. Pilot Mountain, quartzite cap from south

Pilot Mountain quartzite cap from south: source http://www.greensborodailyphoto.com/2011/10/pilot-mountain.html
Pilot Mountain quartzite cap from south: source: http://www.greensborodailyphoto.com/2011/10/pilot-mountain.html

Now let's move our viewing by 90 and look from Little Pinnacle, from the west (rather than the south). This view is along the direction of the strike line and we see the dip of 20 in the quartzite layers.

Figure 17. Pilot Mountain, quartzite cap from west (from Little Pinnacle)

Pilot Mountain quartzite cap from west (from Little Pinnacle): source http://en.wikipedia.org/wiki/Pilot_Mountain_(North_Carolina)
Pilot Mountain quartzite cap from west (from Little Pinnacle): source http://en.wikipedia.org/wiki/Pilot_Mountain_(North_Carolina)

What time of year was this photo taken [28] ?

The caps at the other end of the Sauratown Mountains, in Hanging Rock State Park are also quartzite: Moore's Knob, Moore's Wall, Cook's Wall, Devil's Chimney, Wolf Rock and Hanging Rock [29] . I don't know their dip and strike.

Although the quartzite cap is 200' (65m) thick, the Sauratown Mountain Anticline has been compressed laterally, with evidence of 5 compression events.

Figure 18. Compression and Folding

CGS Field Notes, 1988, p34, Fig 12(b)
CGS Field Notes, 1988, p34, Fig 12(b)

On some parts of Pilot Mtn, the layers are overturned [30] , presumably due to the folding. The original depth of deposition is likely to be substantially less than 65m [31] .

7. Monadnocks

Pilot Mtn is a monadnock [32] (the native american term) or inselberg (island mountain, German) or kopje (little head, Dutch).

A monadnock is an isolated rock hill, knob, ridge, or small mountain that rises abruptly from a gently sloping or virtually level surrounding plain.

Monadnocks have a wide variety of appearances (photos here from wikipedia)

  • Kopje, Serengeti National Park, Tanzania [33]

    Figure 19. Monadnock: Kopje, Serengeti National Park, Tanzania

    Monadnock: Kopje, Serengeti National Park, Tanzania source: https://upload.wikimedia.org/wikipedia/commons/thumb/9/9a/Rock_formation_%28kopje%29.jpg/800px-Rock_formation_%28kopje%29.jpg
    Monadnock: Kopje, Serengeti National Park, Tanzania source: https://upload.wikimedia.org/wikipedia/commons/thumb/9/9a/Rock_formation_%28kopje%29.jpg/800px-Rock_formation_%28kopje%29.jpg
  • Pietra di Bismantova in the Apennines, Italy [34]

    Figure 20. Monadnock: Pietra di bismantova castelnovo monti

    Monadnock: Pietra di bismantova castelnovo monti source: http://en.wikipedia.org/wiki/File:Pietra_di_bismantova_castelnovo_monti.jpg
    Monadnock: Pietra di bismantova castelnovo monti source: http://en.wikipedia.org/wiki/File:Pietra_di_bismantova_castelnovo_monti.jpg
  • the Granitic gneiss dome of Sugarloaf Mountain, Rio de Janeiro [35]

    Figure 21. Monadnock: Granitic gneiss dome of Sugarloaf Mountain, Rio de Janeiro

    Monadnock: Granitic gneiss dome of Sugarloaf Mountain, Rio de Janeiro source: http://en.wikipedia.org/wiki/File:PaodeAcucar.JPG
    Monadnock: Granitic gneiss dome of Sugarloaf Mountain, Rio de Janeiro source: http://en.wikipedia.org/wiki/File:PaodeAcucar.JPG
  • The granitic Spitzkoppe of Namibia, formed by early Cretaceous rifting and magmatism [36] . Note the tilted strata, while Pilot Mountain's strata are nearly horizontal.

    Figure 22. Monadnock: The granitic Spitzkoppe of Namibia, formed by early Cretaceous rifting and magmatism

    Monadnock: The granitic Spitzkoppe of Namibia, formed by early Cretaceous rifting and magmatism source: (http://en.wikipedia.org/wiki/File:2008-06-28_08-18-02_Namibia_Erongo_Usakos.JPG
    Monadnock: The granitic Spitzkoppe of Namibia, formed by early Cretaceous rifting and magmatism source: (http://en.wikipedia.org/wiki/File:2008-06-28_08-18-02_Namibia_Erongo_Usakos.JPG
  • A duricrust inselberg near Dori, Burkina Faso [37]

    Figure 23. Monadnock: duricrust inselberg near Dori, Burkina Faso

    Monadnock: A duricrust inselberg near Dori, Burkina Faso source: http://en.wikipedia.org/wiki/File:De_Yalgo_a_Dori_Marco_Schmidt_0922.jpg
    Monadnock: A duricrust inselberg near Dori, Burkina Faso source: http://en.wikipedia.org/wiki/File:De_Yalgo_a_Dori_Marco_Schmidt_0922.jpg

As you can see, there's nothing particularly unifying geologically about monadnocks. They look very different.

not for presentation

I imagine that the world famous mittens in the Hopi Reservation in Arizona, and Uluru (previously known as Ayer's Rock, till it was returned to its owners) in central Australia are also monadnocks. Is seems that anything rising out of a flat plain is a monadnock. With that definition, is isn't hard to think of other monadnocks. Hanging Rock State Park, at the other end of the Sauratown mountains, has quartzite caps too, but are not described as monadnocks. Presumably this is because the caps are on an extensive area of schist, which already appears as a mountain in its own right. The schist doesn't rise directly out of the plain like Pilot Moutain does.

I had not heard of a monadnock till I came to the mid-atlantic and being a ham radio operator, I found that hams operate in contests from the top of Mt Monadnock in New Hampshire. Strangely there is no mention of Mt Monadnock in the wikipedia page on monadnocks. Here's Mt Monadnock

Figure 24. Mt Monadnock, New Hampshire

Mt Monadnock, New Hampshire. source http://www.qcc.mass.edu/brink/trav-rec/mt_monad/images/Trail-routes.jpg
Mt Monadnock, New Hampshire. source http://www.qcc.mass.edu/brink/trav-rec/mt_monad/images/Trail-routes.jpg

It's not a monadnock in the sense that wikipedia has it. However it's the native american term, so the native americans thought it a monadnock. Maybe the term monadnock shouldn't be used the way we're using it, and we should use the term inselburg instead.

8. Beaches

Pilot Mtn is quartzite, a metamorphosed sandstone. The Pilot Mtn quartzite was deposited on the shores of the passive margin of Laurentia, facing the Iapetus ocean.

Steward and Roberson [38] say that the Pilot Mtn quartzite is 98% silica, indicating that the sand, which became the sandstone and then quartzite, was originally beach sand. They also say, in a not particularly clear way, that the deposition occured, or started 540Mya (i.e. the start of the Cambrian).

I couldn't find anything in my references to support these claims. With regard to the age of the sand, there was scattered information on the age of various layers in the Chilhowee Group at different locations, but nothing about the quartzite at Pilot Mtn. There was quartzite or sandstone as one of several layers at each of these sites. It is likely that the Pilot Mtn quartzite then is only one of several original Cambrian layers. Without dating, it's not possible to say if the Pilot Mountain quartzite was layed down at the same time as the sandstone or quartzite at the other locations. I didn't find anywhere, confirmation of the statement made by Steward and Roberson, that "the Pilot Mtn sand was deposited at or starting at 540Mya".

While Stewart and Roberson say that the quartzite is 98% quartz, indicating a beach, the CGS 1988 field guide says that the quartzite is 90-95% quartz, with the quartzite interspersed with layers of other minerals, i.e. not a beach. The quartzite is not a single massif; it's multiple layers of quartzite with other minerals in between. The presence of the other metamorphosed minerals was used to shows that temperature of the quartzite reached 650 during metamorphosis. It's possible that Stewart and Roberson meant that the quartzite, exclusive of the other rocks, was 98% quartz, but without explicitely saying so, their statement indicates a beach, rather than not a beach, and is misleading.

Even the statement that the sand was deposited on a beach is not supported by the evidence. Stewart and Roberson describe the presence of cross-bedding in the quartzite. At a beach, the reworking of the sand by the waves, would eliminate any cross-bedding. Cross-bedding is expected in estuarine or marine environments (just off-shore), where there is uniform movement of a fluid, but not at a beach. The CGS 1988 field notes [39] has a section describing the evidence for deposition in a lower shoreface to inner shelf (miles out) setting.

Stewart and Roberson's description of Pilot Mountain led me to a simple model of the geology, and an underestimate of the amount of work I'd need to describe the geology there. Their model was incapable of incorporating any of the other information I found about the Park. Bit by bit, I eventually discarded everything geological in Stewart and Roberson and had to start again.

While making a nice story, Stewart and Roberson's statements would appear to be somewhere between an oversimplification and wrong. I was reminded again of the statement of a college professor friend

"Never read the popular press. It's always wrong."

Stewart is a popular and well regarded teacher (from talking to his students). I have met him personally and been with him when he's lead field trips with the Carolinas Geological Society; he is delightful, witty, intelligent and caring. Clearly he has made the world a better place. I expect his book is an attempt to extend the joy of understanding geology to a wider audience. It may seem churlish not to thank him for his efforts. However the book misses it's mark. The book is presumably intended so that people, on taking one of his trips, first learn the geology from his text and then on arrival look on the ground at the referenced geology. Any visit to Pilot Mtn will be a day trip, so the reader of the book should have enough information for a 4 hr visit. Possibly, as happened here, the trip was organised for a group and to save everyone swatting the geological details, someone (me) gives a 1hr talk to the group before the trip. The book then needs to give anough information to build a 1hr talk and references to enough detail in the park for 4hrs of activity. While the information on TV shows and ravens in the park is interesting, in the absence of real geology, it's just filler. Ken needs an editor.

The chapter on Pilot Mtn should have

  • The extent of the quartzite: the whole mountain including the dome underneath Big Pinnacle is quartzite, not just the pinnacles.
  • Where you can see the schist: it starts outside the park, not at the base of the Pinnacles.
  • The direction of the curvature of the anticline (it's transverse to the line joining Pilot Mt to Hanging Rock, not along it). I assumed the ends of the anticline were at Hanging Rock and Pilot Mtn.
  • An explanation for a window (Fig 9.3) that applies to Pilot Mtn. Fig 9.3 requires that the upper (eroded) layer of a window is older than the rocks exposed by the window. A window only required that the upper eroded layer be unrelated to the layer exposed by the window.
  • That there are 4 layers of thrust sheet under the dome. The thrust sheets are associated with pairs of faults and result in two windows.
  • Where to look for cross bedding (it's everywhere, but I didn't know that till I arrived in the park)
  • That the layer of rock at eye level is sandstone and not the expected quartzite and why it isn't quartzite.
  • The correct amount of silica in the quartzite, or an explanation for why their number is different to everyone else's.
  • An explanation for why cross bedding is found in the Pilot Mtn quartzite.
  • Whether the sand was deposited on a beach or off-shore and the evidence for it.
  • Mention of the layers between the quartzite and how they got there.

The explanations don't have to be in the detail of a geology text book, but should be enough to trigger the reader's interest to go find one. On reading the textbook, the reader should recognise that it expands on the information in the guidebook.

However for convenience, I will refer to Pilot beach and the beach environment. I will assume that deposition of the sand occured in the Cambrian without trying to provide a narrower time frame.

Back to the beach:

The obvious question then on the tip of everyone's tongue is "why do we find sand on a beach?" Why aren't all beaches mud? Quartz is a common and resistant mineral. Following erosion, it's found everywhere from the mountains to the continental shelf. So we expect quartz to be on the beach (and everywhere else too). A better question then is "Why is only quartz found in beach sand? What happens to the rest of the minerals?" After all, rivers deliver everything (clay, sand) to the estuary and to the sea. The shore is a relatively high energy environment. The load delivered by the rivers is reworked at the shore. The quartz grains being more resistant and hence large, stay in place, while the finer, lighter material is removed off-shore, where it becomes mud. That the quartz is relatively pure in Pilot Mtn, shows the strong reworking at the original Pilot Beach deposits.

The sand became sandstone, and was buried beneath Shady dolomite (and presumably many other layers). The sandstone was metamorphosed to quartzite. With metamorphosis, you expect the cross bedding in the original sandstone to have gone. However (Stewart and Roberson, Fig 18-3) the bedding planes are still visible. This is because the quartz is mixed in with other minerals (magnetite, ilmenite and rutile: what is called heavy (denser) sands), rendering the cross-bedding visible [40] .

Cross-bedding from wikipedia [41]

In geology, the sedimentary structures known as cross-bedding refer to (near-) horizontal units that are internally composed of inclined layers. This is a case in geology in which the original depositional layering is tilted, and the tilting is not a result of post-depositional deformation.

Cross bedding forms during deposition on the inclined surfaces of bedforms such as ripples and dunes, and indicates that the depositional environment contained a flowing fluid (typically, water or wind). Cross-bedding is widespread in many environments. Environments in which water movement is fast enough and deep enough to develop large-scale bed forms fall into three natural groupings: rivers, tide-dominated coastal and marine settings.

In the CGS notes [42] the extensive cross-bedding is presented as evidence for an off-shore to inner shelf (miles out from shore) environment. At the beach, wave action would destroy any cross-bedding.

There are two types of cross bedding we're interesed in at Pilot Mtn. The first one is called planar, where the cross bedding planes are parallel. Here's an example of planar cross-bedding.

Figure 25. Crossbedding: Dry Fork Dome, Canyons of the Escalante

Cross Bedding. Dry Fork Dome. Canyons of the Escalante. source: https://upload.wikimedia.org/wikipedia/commons/thumb/0/06/DryForkDome.jpg/800px-DryForkDome.jpg
Cross Bedding. Dry Fork Dome. Canyons of the Escalante. source: https://upload.wikimedia.org/wikipedia/commons/thumb/0/06/DryForkDome.jpg/800px-DryForkDome.jpg

The other type of cross bedding visible at Pilot Mtn is called festoon. (I hope I have the geology right here. I also didn't know what a festoon is. It's like a garland - a decorative strip hanging between two points.) In fast flowing river environments, the bottom has ripples. Over time, these ripples move from side to side and up and down the river. The height and wavelength of the ripples is determined by the velocity of the river. The Channeled Scablands [43] which Bob told us about recently, has hills in the valley floor. These hills were eventually recognised as ripples left over from an old river bottom, and enabled calculation of the enormous velocity of the river that periodically emptied Lake Missoula, and helped provide support for Bretz and Pardee's theory for the formation of the Channeled Scablands.

If you cut a vertical section in a river, parallel to the river flow, in what is called the dip direction, you will see planar cross-bedding. If instead you cut vertically across the flow of the river, in what is called the strike direction, you'll see cross bedding that shows how the river moved from side to side. This cross bedding is called festoon.

Here's planar and festoon cross-bedding in the Brazos River of TX [44]

Figure 26. Crossbedding: Brazos River TX: planar and festoon cross-bedding

Cross Bedding. Brazos River TX: planar and festoon cross-bedding. source: http://www.searchanddiscovery.com/documents/Shell2/images/fig10.jpg
Cross Bedding. Brazos River TX: planar and festoon cross-bedding. source: http://www.searchanddiscovery.com/documents/Shell2/images/fig10.jpg

I don't know why we would expect riverine type festoon cross-bedding at Pilot Mtn, however the CGS 1988 field notes say it's present (but not where to look for it). I found something that looks like festoon cross bedding. I don't know whether it's the real thing. It's not as dramatic as in the Brazos river, but then we wouldn't expect it to be. Pilot Mtn was a beach or offshore, rather than a river.

Back to beaches. For those of us, like me, who grew up with short beaches against cliffs pounded by surf, it's hard to imagine a beach with enough sand to make a 200' knob like at Pilot Mountain and cover the Sauratown Mountains with a cap. Apparently, even at the beaches I know, there's lots of sand offshore. Here's some photos of beaches that look more like they're on the way to making quartzite caps. This sand goes for miles inland and presumably for a similar distance off-shore as well.

Figure 27. Nadgee-Howe Wilderness beach at water's edge

Nadgee-Howe beach. source https://plus.google.com/photos/111881666838830095593/albums/5832150303214931537?authkey=CIjBj9uj596RqQE https://lh6.googleusercontent.com/-DIzI8jp6CrQ/UO_3UPsAAVI/AAAAAAAAE6w/Zhk-__D7HLQ/s677/P1060956.JPG
Nadgee-Howe beach. source https://plus.google.com/photos/111881666838830095593/albums/5832150303214931537?authkey=CIjBj9uj596RqQE https://lh6.googleusercontent.com/-DIzI8jp6CrQ/UO_3UPsAAVI/AAAAAAAAE6w/Zhk-__D7HLQ/s677/P1060956.JPG

Figure 28. Nadgee-Howe Wilderness beach back from water's edge

Nadgee-Howe beach. source https://plus.google.com/photos/111881666838830095593/albums/5832150303214931537?authkey=CIjBj9uj596RqQE https://lh4.googleusercontent.com/-gi6ZTKj-z6E/UPCpjzA-2BI/AAAAAAAAE_I/laggGgEAeso/s677/P1070034.JPG
Nadgee-Howe beach. source https://plus.google.com/photos/111881666838830095593/albums/5832361307294304417?authkey=CObPpYDwu6ChzwE# https://lh4.googleusercontent.com/-gi6ZTKj-z6E/UPCpjzA-2BI/AAAAAAAAE_I/laggGgEAeso/s677/P1070034.JPG

As we know, beaches extend for thousands of miles around the perimeter of the continent. In the Sauratown anticline we're only seeing about 20miles of beach.

  • Why are we only seeing 20miles of the quartzite?
  • Where is the rest of the quartzite?

There's a few other questions too.

  • Which rocks eroded to produce the sand?
  • Where was Laurentia?
  • Where was the Iapetus Ocean?

The first question is easy. It don't know. The material came from somewhere in the proto-Appalachian mountains. It had to be some silica/quartz rich rocks. These include granite, gneiss, and schist.

9. Age of Pilot Mtn

leave out of presentation

The book "Exploring the Geology of the Carolinas" is big on the lives of people in TV shows, but the geology isn't pitched to the critically minded. From this paragraph (p137), when was the sand, which became the Pilot Mtn quartzite, deposited on the beach.

Although Pilot Mtn is 2,421' above sea level today, its cliffs originated as white beach sands on the shores of an ancient ocean. About 540Mya, the Iapetus Ocean was lapping at the shores of Laurentia, the continent that later would become N. America. Laurentia's sandy beaches were probably similar to the beaches of the Carolinas today, except they were made up of almost pure quartz grains.

I interpreted this paragraph to say that the Pilot Mtn beaches were formed 540Mya (start Cambrian) and I dug up maps to illustrate the world at the start of the Cambrian. However I couldn't find any confirmation that this is correct. I could only find that it was Cambrian (540-460Mya), but when in the Cambrian I couldn't figure out.

If you read the paragraph carefully, you'll see that the quartzite started as beach sand. You'll also see that that the Iapetus Ocean existed 540Mya. These two sentences are logically unrelated, but consecutive sentences in the same paragraph. If you use logical implication to say that the age of the beach sand is 540Mya, you'll fail your SAT's. Darwinian selection in this country is rapidly weeding out kids, who can't read text like this and who incorrectly conclude that the Pilot Mtn sand was deposited 540Mya [45].

The Pilot Mtn quartzite belongs to a group of rocks extending from TN (Chilhowee) NC, VA (Shenandoah Nat Park), through to MD (Catoctin). I was initially confused and for dating, looked for the quartzite layers in the Cambrian at these places. This is backwards. You look for the date first and then make the connection between sites. Quartzite at one site can still be sandstone at another site.

(Leave out this para: It's likely irrelevant.) A bit of googling shows that the quartzite possibly belongs to the Erwin Formation in the Chilhowee group [46] , but possibly the Erwin Formation is only in N.E. TN in the Unaka belt (I don't know). The Chilhowee group was deposited over a period of 100Mya, starting 540Mya. The Erwin (or Antietam) formation was the last layer deposited. I found webpages giving ages of the Erwin formation from late pre-cambrian to ordovician.

Here's the ages of the sedimentary layers in the Chilhowee Group at Shenandoah Nat Park. Even if the dates don't match those at Pilot Mtn, with a good diagram, there's a chance you'll remember them.

Figure 29. Chilhowee Group at Shenandoah National Park

Chilhowee Group at Shenandoah National Park. source http://www.nvcc.edu/home/cbentley/shenandoah/shenandoah_column.jpg
Chilhowee Group at Shenandoah National Park. source http://www.nvcc.edu/home/cbentley/shenandoah/shenandoah_column.jpg

For this talk, I'm just going to say that the Pilot Mtn sand is Cambrian i.e. 540-460Mya. I don't know anymore detail than that.

(general knowledge question). What plants and animals would we have seen on the shore? The Cambrian is characterised (among other things) by no life on land. As we all remember from important dates in history [47], plants first invaded land in the Ordovician 460Mya. The Pilot beach then was devoid of life. The sun, wind and rain beat down upon bare rock. There was no wood to make a fire or surfboard, animals to make hot dogs out of, or plants to make ketchup. If you were hungry, you could get your trilobiting pole and go trilobiting. They're supposed to taste like locusts.

(general knowledge question). What plants and animals would we have seen on the shore? Since we're talking about the Cambrian (a bit of general knowledge here), what evolutionary event happened 540Mya, that's thought to be responsible for the Cambrian explosion [48] ?



                 plants invade land
450Mya Ordovican ---------------

                 trilobites develope eyes  
                 beach at Pilot Mtn
540Mya Cambrian  ----------------

A few minutes ago I said that the beach was formed at the passive margin. I take it from the silence in the audience here that everyone knows what a passive margin is. I'm quite impressed. I had to look it up [49] .

The margin is the place where the continent meets the ocean floor.

  • At an active margin, like on the west coast of S.A., the ocean floor subducts under the continent, producing the high relief Andes. This is called an active margin.
  • On the east coast of S.America, the ocean floor meets the continent, but there is no subduction. As material comes out of the mid-Atlantic ridge, the ridge moves eastward, but nothing happens to the continent. This is called a passive margin. A passive margin is characterised by a wide continental shelf, built up by deposition on the ocean floor and an extensive flat area on that side of the continent caused by erosion of low relief landforms.

The rock in the Pacific Ocean floor subducts under S.A. at the active margin and rises to become a volcanoe in the Andes. The volcanoe is then eroded and carried by an extensive river system across a flat continent, to be deposited on the continental shelf in the Atlantic. Thus minerals are transported from the Pacific to the Atlantic Ocean.

The reason you need to know all this, is that Laurentia has had a passive margin on the east coast, starting at the time of the breakup of Rodinia about 1Gyra and that Pilot beach was one part of a wide erosional plain, from the proto-Appalachian mountains to the continental shelf. The continential shelf on the US east coast then is about 1Gyr old.

10. Laurentia, Iapetus Ocean

leave out of presentation

Where was Laurentia? Here's a graphic showing the location of Laurentia and it's relationship to the other landmasses 600Mya (near enough to 540Mya for our purposes). This is a small patch of a larger image I found linked from Jeffrey Reid's site [50] .

Figure 30. Laurentia 600Mya according to the NC State Board of Education

NC Through Time, 600Mya. source http://www.jeffreycreid.com/NC Through Time.PDF
NC Through Time, 600Mya. source http://www.jeffreycreid.com/NC Through Time.PDF

The whole image shows the movement of the continents over the last 600My and was produced by the NC State Board of Education in cooperation with the NC Department of the Environment and Natural Resources. It's designed to educate high school kids. When you look at this slide you find that most of the land mass is on the edge of the image, and with the projection used, it's difficult to determine which continent is which. We can all guess from this graphic that Laurentia is in the center of the image. What are the two land masses adjacent to Laurentia? You won't find out from this graphic. Africa, S. America, Antarctica, India and Australia are recognisable in most of the continental arrangements over the last 600Mya. Where are they on this graphic? What is the continent at 5o'clock in this diagram? The State Board of Education thinks that this is going to help students. It's not. This graphic gets an F. The graphic has a featureless ocean as the central object of the image. The center of the image should be moved, so that the continents on the lower right edge are surrounded by ocean. This is a graphic drawn by someone who thinks the rest of the world doesn't matter. It should never have been drawn. All this graphic does is add to the hopelessness that students feel as they try to master the impossible tasks that clueless adults put upon them.

The center of this map apparently is favoured by a few people. Here's a similar map from 514Mya, but this one is labelled

Figure 31. Laurentia 514Mya

Laurentia 514Mya. source http://scotese.com/images/514.jpg
Laurentia 514Mya. source http://scotese.com/images/514.jpg

We can see Laurentia, the Iapetus Ocean and the two continents near Laurentia. They are Siberia and Baltica. Note that England, Wales, Florida and the US New England and Nova Scoia are all together attached to Africa and S. America. Due to the projection used and the center chosen for the projection, N China and S China are on the opposite side of the map.

Here's another view with a different center of projection. (Note it's only a hemisphere. Presumably if the whole earth was shown, most of the rest of the map would be ocean, which would help put the location of the continents in perspective.)

Figure 32. The Earth 550Mya

The Earth 550Mya. source http://www.clas.ufl.edu/users/jmeert/550.jpg http://en.wikipedia.org/wiki/File:Positions_of_ancient_continents,_550_million_years_ago.jpg
The Earth 550Mya. source http://www.clas.ufl.edu/users/jmeert/550.jpg http://en.wikipedia.org/wiki/File:Positions_of_ancient_continents,_550_million_years_ago.jpg

Here's an animation of the movement of the continents since the start of the Cambrian. Tutorial 22.1 Evolution of the Continents (http://bcs.whfreeman.com/thelifewire/content/chp22/22020.html)

11. Windows and Crashing Rocks

The Sauratown anticline is in the middle of the Sauratown Window. The Sauratown Window is part of a thrust system. Thrust systems are one of the mechanisms of mountain building. Here we're going to learn about windows and thrust systems.

do not use in presentation

First here's the Grandfather Mountain window as explained by Stewart and Roberson The Grandfather Mountain window and this diagram represent a simple system and it's one given in basic geology texts.

Figure 33. Grandfather Mountain window

Stewart and Roberson Fig 9.3 The Grandfather Mountain window
Stewart and Roberson Fig 9.3 The Grandfather Mountain window

To explain a window, you need two layers of rocks. In the Grandfather Mountain Window, the upper layer is the older Lindville Falls thrust sheet, which has moved in from the east, covering the younger rocks. Following this, there was localised uplift, and then erosion of the elevated land. The removal of the upper layers reveals the rocks in the younger strata below. The area where the upper layers have been removed is called a window.

Here's diagram of a thrust system from wikipedia showing a window [51] .

Figure 34. Thrust System

Thrust System. Source https://upload.wikimedia.org/wikipedia/commons/thumb/b/b1/Thrust_system_en.jpg/800px-Thrust_system_en.jpg
Thrust System. Source https://upload.wikimedia.org/wikipedia/commons/thumb/b/b1/Thrust_system_en.jpg/800px-Thrust_system_en.jpg

A nappe (from Fr tablecloth) [52] is a sheet of rock that's been moved more than 2km. A klippe [53] is the remnant portion of a nappe after erosion has removed connecting portions of the nappe.

not for presentation

Although this looks similar to the Grandfather Mountain window diagram, there's something you need to know or you won't understand the Sauratown Mountain window.

In the Grandfather Mountain window, older rocks rest upon younger rocks. Erosion of the older rocks revealed the younger rocks below, as if looking through a window. The critical feature of a window is not that you see through older rocks to younger rocks, but that you see through to rock belonging to a different formation. The relative ages of the rocks is irrelevent.

As a counter example, this is not-a-window: in a sedimentary system like the Grand Canyon, say you had uplift in the center, to produce an anticline, followed by erosion to produce a flat surface, revealing the conformal layer below. In this case, You do not have a window, because the two layers, the now visible layer and the eroded layer above it, are related (here they're conformal). In this example of the Grand Canyon, you have an eroded anticline, not a window.

We'll come back to the Sauratown Mountain window in a minute. First we need to know about crashing rocks (thrust systems). There's a few new terms involved here: imbrication, duplex and horse.

Here's a diagram showing imbrication (shingling). Following thrust faulting, one layer is thrust over itself, producing shortening of the crust and mountain building. The faults associated with thrusting are near horizontal, rather than the near vertical faults associated with slip-strike faults or crustal extension.

Figure 35. Imbricated Fan

Imbricated Fan. source: https://s3.amazonaws.com/classconnection/665/flashcards/343665/jpg/imbricate_fan1321478769729.jpg
Imbricated Fan. source: https://s3.amazonaws.com/classconnection/665/flashcards/343665/jpg/imbricate_fan1321478769729.jpg

Figure 36. Imbricated Fault

Imbricated fault source: http://www.kellogginternational.com/userfiles/image/imbricate%20fault.jpg
Imbricated fault source: http://www.kellogginternational.com/userfiles/image/imbricate%20fault.jpg

In the diagrams above, a single thrust sheet is piled up in several layers. This happened at Pilot Mtn, where there are 4 layers of the same thrust sheet under the mountain.

There's two new words associated with this diagram: duplex and horse. The name duplex comes from the double storeyed wall-to-wall (to prevent from cold) houses built first in Canada and then built probably everywhere else in the world [54] . A duplex is a system of imbricated (overlapping) thrusts that branch off from a single fault below and merge with a thrust fault above [55] . A duplex then is a thrust sheet with a fault above and below.

A horse is the geological technical term used for any block of rock completely separated from the surrounding rock either by mineral veins or fault planes [56] . Here's a diagram showing a horse.

Figure 37. Horse

Horse source: https://upload.wikimedia.org/wikipedia/commons/thumb/c/cc/Duplex1.png/800px-Duplex1.png
Horse source: https://upload.wikimedia.org/wikipedia/commons/thumb/c/cc/Duplex1.png/800px-Duplex1.png

A horse and a duplex appear the same to me. There can be multiple layers of duplexs, not just two layers, with each layer being a horse.

Here's an animation of a duplex forming

Figure 38. Duplex formation: animation

Duplex formation: http://www.earth.lsa.umich.edu/~vdpluijm/animations/thrustduplex_ani.gif
Duplex formation: http://www.earth.lsa.umich.edu/~vdpluijm/animations/thrustduplex_ani.gif

Here's an example of a thrust fault duplex, near Albany, NY, within the Hudson Valley fold and thrust belt.

Figure 39. Thrust fault duplex, Hudson Valley fold and thrust belt.

Thrust fault duplex source http://web.cortland.edu/gleasong/qthrust.jpg
Thrust fault duplex source: http://web.cortland.edu/gleasong/qthrust.jpg

In case you haven't got thrust systems already, I'm going to show you some more diagrams, just to let you know the neat stuff people have put on the web (and to reinforce what you've learned so far). These are a set of animations [57] on webpages about the classic Moine Thrust Belt in Scotland [58] .

  • Rampflat (http://www.see.leeds.ac.uk/structure/assyntgeology/geology/thrusts/what/rampflat.htm)
  • duplexes (http://www.see.leeds.ac.uk/structure/assyntgeology/geology/thrusts/what/duplex1.htm)
  • duplex2 (http://www.see.leeds.ac.uk/structure/assyntgeology/geology/thrusts/what/duplex2.htm)

    This example looks like Pilot Mountain. If you erode the top, but leaving Pilot Mtn, you have a window looking through to the rocks below. The thrust sheets are duplexes sitting between thrust faults. After erosion, the fault lines are oriented at right angles to the direction of the thrust (which was from the east), and are situated in pairs symmetrically about the middle of the anticline.

  • large scale thrust faulting (http://www.see.leeds.ac.uk/structure/assyntgeology/geology/thrusts/what/large-scale.htm)

There were 3 collisions between Gondwana and Laurentia; the Taconic, Acadian and the Alleghenian. The Taconic just pushed the Carolina terraines onto Laurentia. The Carolina terraines came from the Amazonian side of Gondwana. This wasn't particularly dramatic. There were volcanoes and back island arcs, but that was about it.

You know how when your car hits a deer and parts of the car get pushed up and back? During the Alleghenian (300Mya), Africa was on the side of Gondwana facing us and it crashed into Laurentia. Even the rocks got out of the way. The rocks rose 20,000', to produce near Himalayan sized mountains and were shoved back (westward) shortening the crust by 150 miles. The beach where the Pilot Mtn sand was deposited, came from 150miles east of where Pilot Mtn is today.

note for presentation

We know that geologists can tell this sort of thing, because they can be walking along and one of them will pick up a grey pebble and look at it with his magnifying glass and say "I saw a rock just like that about 25yrs ago 150miles from here". The other geologists will take their turn and they'll say "yes I remember that rock too". Geologists walking across a glacier or ice field in the Antarctic do the same thing all the time. One of them will spot a black speck of sand, pick it up and say "this meteorite came from Mars" and sure enough, all the rest of the geologists, none of who have ever been to Mars, will say exactly the same thing. This seems amazing to me, but geologists do this all the time.

When I grew up in Australia, on the news on the TV about every 6 months, we would hear a story from the US, about cars piling up on the freeway in the fog, with the cars colliding for 30mins, till the whole fogged area was filled with crashed cars. Movies from a helicopter later flying over the scene would show miles and miles of crashed cars pushed on top of each other and jack-knifed semi-trailers. People living in the vicinity would say that they heard the crashing and grinding going on forever. The same thing happened in the Alleghenian orogeny, but the crashing and grinding went on for 100My over a distance of 150miles.

Normally it only takes 20My to erode away a mountain. They don't last long under the onslaught of rain and sun. As you can see, there isn't much left of the 20,000' Appalachian Mountains, but Pilot Mt did poke through about 10Mya and will probably last another 2Myr. The rest of the Appalachians became sediment for the coastal plain and off-shore. The sediments at Cape Hatteras are about 10,000 feet thick and they extend off shore to the continental shelf. This is typical of the passive margin of the continent. We live where everything has been worn down.

I birdwatch and ocassionally go on pelagic trips where you see birds that you don't see on land. You only have to go a mile offshore, for the birds to be completely different. There's not a land bird to be seen and instead you see albatrosses, petrels, shearwaters... I've only been off the coast of Sydney, where it doesn't take long to get to the edge of the continental shelf. I've asked about pelagic trips here, but they aren't real popular and don't run real often. The reason is that the continental shelf here is so much further offshore and it takes forever just to get there and back. Throwing up for 4 hrs in each direction is not a lot of fun, but just about everyone will accept throwing up for 2hrs each way to see a few new birds. The reason then that there are no pelagic birding trips off the Carolinas is the geology, specifically the passive margin.

Under the Sauratown Mountains, there are four layers of thrust sheets. The rocks are late proterozoic (1.2Gya) but were thrust underneath during the Alleghenian orogeny (300Mya) when Africa crashed into N.A. Although the 4 layers all come from the same sheet, remember that 150miles of crustal shortening were involved. The original material in the thrust sheets came from the proto-Appalachian mountains and were sedimented in a gradient from the mountains to the edge of the continental shelf. The metamorphosed sediment would have varied throughout the gradient, with quartz sand at the shoreline and carbonates off-shore. After metamorphosis, the sediment became the laterally differentiated material for the thrust sheet.

Although there's 4 layers of thrust sheet below Pilot Mtn

  • all layers came from one original thrust sheet
  • the age throughout each layer in the sheet will be similar
  • there is lateral differentiation in the original deposition profile which was metamorphosed to became the thrust sheet
  • this was followed by the pile up of 150miles of the sheet into 4 layers
  • the minerals and rocks in each layer at any location, will be different, because of the original lateral gradient

before

mtn.......................shelf
A B C D E F G H I J K L M N O P  new
a b c d e f g h i j k l m n o p  old

after

mtn..shelf
/__
M N O P new
m n o p old
/__
I J K L new
i j k l old
/__
E F G H new
e f g h old
/__
A B C D new
a b c d old

Each thrust sheet contains an intact stratigraphic sequence composed of middle proterozoic basement and a non-conformally overlying cover sequence of upper proterozoic/lower cambrian metasedimentary and metaigneous rock. [59]

12. Peneplain, Pediment

not for presentationa

The coastal and off-shore area of NC is a plain of sediment derived from the 20,000' thick Appalachian Moutains. The inner piedmont is similarly flat, but is the result of erosion down to bedrock in a long period of tectonic stability. There are two versions of this

  • peneplain [60] which has a convex surface.
  • pediment [61] which has a concave surface.

The Inner Piedmont is a peneplain. I haven't been able to figure out when you get a convex surface and when you get a concave surface.

Here's a well known peneplain, the Australian shield, with a monadnock, an uneroded lump of sandstone embedded in it. The strata in the sandstone are tilted at 90.

Figure 40. Uluru

Uluru in a peneplain. source:http://geology.about.com/library/bl/peaks/bluluru.htm http://0.tqn.com/d/geology/1/0/C/B/uluru.jpg
Uluru in a peneplain. source:http://geology.about.com/library/bl/peaks/bluluru.htm http://0.tqn.com/d/geology/1/0/C/B/uluru.jpg

13. Sauratown Window

Under the Sauratown Mountains are 4 mid- and late-proterozoic imbricated thrust sheets (Flint Hill, Little Yadkin, Pinnacle and Volunteer) are overlain non-conformably by sedimentary and volcanic rocks [62] . The sedimentary rocks include the Pilot Mtn quartzite.

Exposed in the eroded crest of the Sauratown Mountains anticlinorium are portions of four imbricate and stacked thrust sheets, which document considerable (crustal) shortening by thrust imbrication. Following their emplacement, the thrust sheets were domed by deformation associated with the formation of the Sauratown Mountain Anticlinorium, and subsequent erosion has exposed a complex window. [63]

The faults are nearly horizontal and intersect the surface, symmetrically about the window, in lines running at right angles to the direction of the thrust. The younger (500Mya Cambrian) Pilot Mtn quartzite sits on top of multiple layers of older (1.2Gya) proterozoic rocks that were moved in underneath by thrust faulting in the Alleghenian orogeny 300Mya. On the average, younger rocks are on top of older rocks. Erosion has allowed us to look through to unrelated sequences of rocks underneath. Here's the cross-section through the Sauratown window showing the imbricated strata. The top of the diagram is the level of erosion that was reached about 10Mya. Pilot Mtn pokes above the horizon and is not shown on the scale of the map.

Figure 41. Cross-section through Sauratown Mountains window from 1988 CGS guide book

Cross-section. Sauratown Mountains Window from 1988 CGS guide book, p3, Fig 2B
Cross-section. Sauratown Mountains Window from 1988 CGS guide book, p3, Fig 2B

There are two pairs of faults symmetrically about the center of doming. The inner pair are the Danbury thrust faults. The outer pair are the Forbush thrust faults. These two pairs of faults expose two strata in the window. These two strata are called the inner and the outer window.

Here's a simplified tectonic map showing the inner Hanging Rock window and the outer Sauratown Mountains window, with stops on the field trip. Stops 11-14 are at Pilot Mtn and we'll see them on our field trip.

Figure 42. Tectonic map: Sauratown Mountains window from 1988 CGS guide book

Tectonic map: Sauratown Mountains Window from 1988 CGS guide book, p3, Fig 2A
Tectonic map: Sauratown Mountains Window from 1988 CGS guide book, p3, Fig 2A

leave out of presentation

Here's a geological map of the Sauratown Window. On this scale, both Big Pinnacle and Little Pinnacle are too small to be seen.

Figure 43. Sauratown Window

Sauratown Window, CGS Field Notes, p44, Fig 1
Sauratown Window, CGS Field Notes, p44, Fig 1

Presumably the beach sand that was the shore in the late Cambrian should continue in a NE-SW direction from Pilot Mtn, but be buried. Phil Bradley, of the NCGS, says that no-one has done the drilling to follow the old shoreline. However the Chilhowee sandstone and the Lindville quartzite (the lower, younger layer at Lindville Falls) are expected to be part of the same original beach sand. The Chilhowee group extends from Chilhowee Mountain (TN) to Catoctin Mountain (MD) [64] , with occasional outcroppings at Jefferson's Stairs (Harper's Ferry, WVa), Blackrock (Shenandoah National Park, VA) and Catoctin Mountain (MD, where I used to ride my bicycle in weekends, but I was oblivious of the relevance of the mountain).

I'm not sure of the relevence of this section to Pilot Mtn and I'm not going to use it in the talk.

Here's a paragraph from "Hiker's Guide" describing the formation of the Chilhowee group. Presumably the Pilot Mountain beaches were part of this.

The Chilhowee Group was deposited over the course of almost 100 million years as the Iapetus Ocean formed and the proto-Appalachian mountains eroded. About 450 million years ago, in the middle of the Ordovician Period, the North American and Eurasian plates stopped opening and started to close. Through sequences of three orogenies (Taconic, Acadian, and Alleghenian) over the course of 200 million years, the strata were subjected to a series of diastrophic events, producing the folding and faulting that created the Appalachian Mountains and the supercontinent known as Pangea. It (presumably Pangea) persisted for about 50 million years, its breakup resulting in the formation of the Atlantic Ocean and the eroded topography of the coastal plain.

Diastrophism refers to deformation of the Earth's crust, and more especially to folding and faulting. Diastrophism can be considered part of geotectonics. Diastrophism comes from the Greek word meaning a twisting [65] .

Again from Hiker's Guide, the lower formation, the Weaverton Formation is 100-500' thick and laid down in a riparian (river) environment.

The first layer to be deposited was the Weverton Formation, a 100 to 500 foot thick bed of pebbled quartzite with stratified layers of phyllite and metasandstone. The coarseness of the grain is an indication of the riparian origin of the initial formation, the sand, pebbles and gravel accumulating in the initial rivers flowing from the uplifted areas to the newly forming Iapetus Ocean. The Weverton Formation is named for Weverton, Maryland, and forms the main ridge-making formation in Eastern Maryland. Wolf Rock in Catoctin Park (right) is a prime example.

From Hiker's Guide, the middle (Harper's) formation, was deposited in a littoral (sea shore environment) and is the thickest layer 1800-2200' thick. The fine grain shows that the sediment was deposited in a quieter environment.

It consists of drab, dark layers of phyllite and greenish-gray to brown metasiltstone. The finer grain structure of the formation is characteristic of a littoral deposition in muddy lagoons that were formed as the Iapetus Ocean rose, sand, silt and mud collecting in thick layers. The formation is prevalent in the area around Harper's Ferry (the stairs to "Jefferson Rock" are cut into the cleavage of the bedding planes) from which its name is derived. Blackrock (right) is the most striking example of the formation in Shenandoah National Park.

From Hiker's Guide, the top (Erwin or Antietam) formation, is 1000' thick and is the result of westward extension of the shoreline, filling in muddy lagoons.

The Erwin or Antietam Formation is the third and final layer of the Chilhowee Group, consisting of thick beds of nearly white quartzite that form distinct cliffs on many of the upper ridges of Shenandoah National Park (left from Skyline Drive and top above on Brown Mountain). The geologic sequence that is manifest in the formation is the extension of the seacoast westward, covering the muddy lagoons that formed the underlying Harpers Formation with beach sand that accumulated to depths of up to 1,000 feet. The relative purity of the quartzite supports this explanation, as the nearly pure white silica particles result from neritic wave action [66] that creates beach sand.

This says that Brown Mountain, just north of the Sauratown Mountains, has Antietam Formation quartzite. Presumably this is the same quartzite as found at Pilot Mountain.

Note
Is this true?

We've found that we only see 20miles of the quartzite because it was exposed by the Sauratown Window. We've found that the old shoreline which is now the Chilhowee group extending from Eastern TN to MD, was deposited by erosian of the proto-Appalachian mountains over a period of 100My starting about 550Mya (the start of the Cambrian).

14. Schist

The layer underneath the Pilot Mtn quartzite is 1.2Gya schist. The geology is more complex and to geologists more interesting, but to people like me it's more complex than I can handle. I decided to leave for another time its formation and what happened in the intervening 700My till the arrival of the sand at Pilot beach. But just to refresh your memory, here's what the continents looked like back then. The supercontinent is called Rodinia.

Figure 44. Rodinia

Rodinia 1.2Gya. source: http://upload.wikimedia.org/wikipedia/commons/a/a4/Rodinia_reconstruction.jpg
Rodinia 1.2Gya. source: http://upload.wikimedia.org/wikipedia/commons/a/a4/Rodinia_reconstruction.jpg

15. Field Trip

Photos are from a reccy I did at the end of January (when I was lucky enough to arrive on a day when the park was closed by snow) and from the day itself (23 Feb 2013).

15.1. Grassy Creek, CGS Stop 12, 36.948N, 80.455W

Note
This is private property. Please get permission from the land owner before entering.

The first thing a geologist does when mapping an area is walk the creeks. The flowing water exposes the rocks. The creeks are also full of vines, thorns and fallen trees.

As I said previously, the junction between the lower proterozoic schist and the upper quartzite is not at the basement of the knobs. Instead it's outside the park. The dome and slopes under the Knobs are quartzite too. We can see the junction between the quartzite and schist at stop 12 on the CGS field notes. This is at the spillway of the lake on Grassy Creek. We are there to look at the junction of the lower black gneiss and the upper white quartzite. The U-Pb age of the Grassy Creek gneiss is 1G17ya [67] . There are augen in the gneiss [68] .

Figure 45. Pilot Mtn quartzite/gneiss boundary

CGS Field Trip 1988, p78 Stop 12, google maps
CGS Field Trip 1988, p78 Stop 12, google maps

Here's the spillway. The rocks and the unconformity we're interested in are to the left.

Figure 46. Grassy Creek Spillway

CGS Field Trip 1988, p78 Stop 12, Grassy Creek Spillway
CGS Field Trip 1988, p78 Stop 12, Grassy Creek Spillway

Here's the lake to the right of the spillway.

Figure 47. Grassy Creek Dam

CGS Field Trip 1988, p78 Stop 12, Grassy Creek Dam
CGS Field Trip 1988, p78 Stop 12, Grassy Creek Dam

This photo is from the field trip. We're just below the dam.

Figure 48. Diane above gneiss

Diane above gneiss
CGS Field Trip 1988, p78 Stop 12, Grassy Creek Dam

If we go downstream of the spillway (need shoes for wet rocks), you look back at this spot. (Diane was standing above the bank to the right.)

Figure 49. Grassy Creek downstream of spillway

CGS Field Trip 1988, p78 Stop 12, Grassy Creek downstream of spillway
CGS Field Trip 1988, p78 Stop 12, Grassy Creek downstream of spillway

Immediately to the right and left of us in this photo, there is a sloping bed of small grained red gravel, with cross-bedding. It's saprolytic gneiss.

Figure 50. Grassy Creek cross bedded gravel

CGS Field Trip 1988, p78 Stop 12, cross bedded gravel
CGS Field Trip 1988, p78 Stop 12, cross bedded gravel

Just downstream a few more feet, is rock that breaks into rectangular prisms. I assume this is the schist/gneiss. (I don't have a photo).

The title in the CGS notes (p78) for this stop "Unconformity between late proterozoic basement and cover sequence", led me to believe we would see the unconformity, but no-one could see it. The only mention in the notes (p80) that could be to an unconformity say "West of the Grassy Creek gneiss are exposures of the Sauratown mountains...". Well how far west; 10m? in the park?

not for presentation

I've spent much of my life hiking and I know I've been past all sorts of wierd things like this in my life. I just go "meh. more rocks" and keep walking. I spent 5yrs in high school, learning french, which I've never used, and knew I'd never use. Scouts taught me all sorts of things, how to look after myself in the bush, extensive first aid, since Scouts guaranteed to parents that their kids would come home in good shape. Scouts taught me to recognise birds and trees. Not once was the earth you walked, on every day, ever mentioned. My son 40yrs later went through the same educational system, instead learning Spanish. This just goes to show that education is too important to be left to the adults. The kids know best.

15.2. Diamictite, Pilot Mtn road inside park, CGS Stop 14, 30.345N, 80.473W, el 1643'

I was fortunate to get to the park straight after a snow fall. Due to the hazardous conditions, the road was closed to cars, so I walked up. I was risking life and limb to check out the park for the upcoming field trip. I just about had the park to myself. The road was dry, but after some searching, I found a patch of ice at the top, obviously the one which closed the road. The only people who braved the horrific conditions, besides myself, were cyclists, who in the absence of cars, were setting world land speed records down the hill, and rangers, whose life was presumably regarded as expendable by the govt and who drove up and down the perilous hill several times.

The first stop in the park, is a turnout on the way upto the top. It's stop 14 on the CGS field trip. There we see what appears to be basement rock in the middle of the quartzite in a rock called diamictite. Diamictite is a sedimentary rock of non-sorted or poorly sorted sediment. Often such rock is produced by submarine mass flows although no origin is suggested for this rock [69] . So we have some metamorphosed clay in the middle of the quartzite.

Figure 51. Pilot Mtn Diamictite member of Sauratown Formation

CGS Field Trip 1988, p82 Stop 14, google maps
CGS Field Trip 1988, p82 Stop 14, google maps

Although it's not obvious in this photo, the rock has been concertina squashed to form folds. It's this folding that leads people to think that the original thickness of rock that produced the Knobs was thinnner than the current 200'. The dip on the rocks, as for most rocks in the park, conforms to the shape of the dome.

Figure 52. Pilot Mtn Diamictite folds

CGS Field Trip 1988, p82 Stop 14, folds in rocks
CGS Field Trip 1988, p82 Stop 14, folds in rocks

Here's a photo from the day showing clasts in the diamictite.

Figure 53. clasts in diamictite

clasts in diamictite
CGS Field Trip 1988, p82 Stop 14, clasts in diamictite

Here's a photo from the day showing folds in the diamictite.

Figure 54. folds in diamictite

folds in diamictite
CGS Field Trip 1988, p82 Stop 14, folds in diamictite

15.3. stratigraphy of Big Knob

Despite the apparent homogeneity of the Pilot Mtn quartzite, it's not a single massif, but has multiple layers, separated by thin layers of non-quartzite. Geologists find lots of differences in the layers. It's hard to expect the same sea shore for 100Mya, without the ocassional hurricane, change in climate or movement of rivers. Here's the stratigraphy of the Big Knob quartzite.

Figure 55. Pilot Mtn quartzite stratigraphy

CGS Field Trip 1988, p50, Fig 4.
CGS Field Trip 1988, p50, Fig 4.

One of the things that struck me on arriving in the park, is that there's lots of soil and vegetation. With the large slope of the land and the soil being derived from quartzite, which forms poor soils, I would have expected that any weathered rock be eroded away, before it became soil. However according to Phil Bradley, there's enough schist in the quartzite to make soil.

15.4. Pilot Mtn Big Pinnacle, CGS Stop 13

The last stop is at the parking lot at the top of Pilot Mtn State Park, where we finally see Big Pinnacle for the first time, and can walk the Jomeokee trail and the Ledge Spring Trail. The quartz has cross bedding and beds of blue quartz bearing conglomerate. The quartz layers are 0.5-3m thick, interbedded with muscovite schist upto 15cm thick. F2 folds can be seen on traverses on the western slope of Pilot Mtn (I assume this is the sloping bit, not the pinnacles).

Figure 56. Pilot Mtn: Big Pinnacle

CGS Field Trip 1988, p80 Stop 13, google maps
CGS Field Trip 1988, p80 Stop 13, google maps

Here we are on the day. The ranger lined this one up for us. We had great weather. It had been raining all week in town and at the mountain. The forecast for town was rain all that day but on the mountain, the rain was supposed to taper off about 10am, just when we arrived. Knowing that a day outside in bad weather is better than a day inside in good weather and that anyhow there is no such thing as bad weather, only bad clothes (old Norwegian saying), the trip went ahead anyhow. When we got to the moutain, the rain had stopped. I was surprised to find the park covered in snow, the tree limbs covered in ice. The park had been closed the day before. The weather report for nearby Mt Airy hadn't mentioned snow. Much to the amusement of everyone else, I had forgotten about the 1400' elevation difference between the mountain and the town of Mt Airy. The only problem with the weather was that we were surrounded by fog and we didn't see Pilot Mtn on the way in or out, or while we were there. Other than that, the weather was perfect.

Figure 57. The field trip members

Field trip members
L-R Diane Willis, Paula La Point, Jim Dooley, Lynne Duncan, Steve Duncan (in back), Joe Mack

Here's the Jomeokee trail itself. What vegetation in this photo (mid ground, on left of trail, foreground on left) is unexpected for this location [70] ?

Figure 58. Pilot Mtn: Jomeokee trail

CGS Field Trip 1988, p80 Stop 13, Jomeokee trail (C) Joseph Mack
CGS Field Trip 1988, p80 Stop 13, Jomeokee trail (C) Joseph Mack

Here's some cross bedding. It's not particularly dramatic, but that's what we've got. This rock looks a lot like sandstone to me. I was not expecting sandstone, only quartzite. By the time I got to the Ledge Spring Trail I'd seen enough of it that I tested it, to find that indeed there is sandstone all over the place. On consulting the CGS field guide [71] I find sandstone is supposed to be there. It's also shown in the stratigraphy diagram above, in the lower layers of the Knob quartzite.

Phil Bradley says that all the rock there went for the same 650C tectonic ride and all of it would have been converted to quartzite. (The temperature comes from the temperature required to metamorphose the index rock schist in the quartzite; the amphibolite area in the metamorphism phase diagram [72] ) Any sandstone present would be saprolytic quartzite (quartzite that has been weathered back to sandstone, by removal of the cement).

Figure 59. Pilot Mtn: Jomeokee trail planar cross bedding 36.3398N, 80.4754W

CGS Field Trip 1988, p80 Stop 13, Jomeokee trail cross bedding (C) Joseph Mack
CGS Field Trip 1988, p80 Stop 13, Jomeokee trail cross bedding(C) Joseph Mack

Here's some (what I think) is festoon cross bedding. It's not dramatic.

Figure 60. Pilot Mtn: Jomeokee trail festoon cross bedding 36.3407N, 80.4746W

CGS Field Trip 1988, p80 Stop 13, Jomeokee trail festoon cross bedding (C) Joseph Mack
CGS Field Trip 1988, p80 Stop 13, Jomeokee trail cross bedding(C) Joseph Mack

Another photo from the day. Here's some plants that locally are only found on Pilot Mtn. They bloom in May according to the ranger.

Figure 61. mountain laurel (top back), rhododendron (bottom)

mountain laurel (top back), rhododendron (bottom) (C) Joseph Mack
mountain laurel (top back), rhododendron (bottom)

Another photo from the day. About here, the ranger made some raven calls, whereupon some ravens flew over us.

Figure 62. table pine growing out of cliff

table pine growing out of cliff (C) Joseph Mack
table pine growing out of cliff

At this stage on the day, everyone wanted lunch, so we sat in the van and admired the fog. After lunch, everyone else agreed that as a result of the weather, they'd seen all they wanted to see for the day and didn't need to see the Ledge Spring trail and were happy to go home. If only I'd known, I would have done the Ledge Spring trail while everyone else was eating lunch. We were back by 3pm, returning to a dreary day of rain. I'm glad we didn't stay in town for the day.

15.5. Pilot Mtn Big Pinnacle, Ledge Spring Trail, side along the bottom of the cliffs

Ledge Spring Trail. I couldn't get any GPS fixes on the Ledge Spring Trail at the bottom of the cliffs. I would have thought with half the sky visible (even if in trees, with no leaves), that I should have been able to get a fix.

This trail goes along the sloping western ridge of quartzite cliffs. On the south side of the ridge, you walk at the base of the cliffs. On the north side, the trail is on top of the cliffs. In some spots the rock is sandstone rather than quartzite [73].

This photo is not exactly geology, but it looked nice. From the pile of ice at the bottom, the whole face had been covered in ice till recently.

Figure 63. Pilot Mtn: Ledge Spring Trail Ice Fall

Ledge Spring Trail ice fall (C) Joseph Mack
Ledge Spring Trail ice fall (C) Joseph Mack

A rockclimber on a 5.9 pitch. I asked the belayer how their fingers were in the cold. They said it was OK now, but had been colder early in the morning.

Figure 64. Pilot Mtn: Ledge Spring Trail Rockclimber

Ledge Spring Trail rockclimber (C) Joseph Mack
Ledge Spring Trail rockclimber (C) Joseph Mack

Another ice fall on the Ledge Spring Trail.

Figure 65. Pilot Mtn: Ledge Spring Trail Another Ice Fall

Ledge Spring Trail another ice fall (C) Joseph Mack
Ledge Spring Trail another ice fall (C) Joseph Mack

15.6. Pilot Mtn Big Pinnacle, Ledge Spring Trail, side on top of cliffs

On the way back, I walked along the top of the cliffs. There seems to be plenty of squirrel food.

Figure 66. Pilot Mtn: Ledge Spring Trail acorns

Ledge Spring Trail acorns (C) Joseph Mack
Ledge Spring Trail acorns (C) Joseph Mack

16. Conclusion

If you want to have a good field trip, go in winter after it's snowed, the park is buried in ice and the roads are closed. There's no leaves on the trees, you can see the rocks and you have the place to yourself. Take your bicycle.

17. Questions

  • How many nesting pairs of ravens are at Raven Rock State Park? [74]
  • How do you get to the top of Big Pinnacle? [75]
  • What are the Saura best remembered for? [76]
  • What is the difference between a deer and a human riding a bicyle? [77]
  • (6th grade general knowledge question for people who were asleep.) What is the capital of Burkina Faso (the country with the duricrust monadnock)? [78]
  • Why are beaches made of sand? [79]
  • What was the Iapetus ocean surf like at the Cambrian Pilot beach? [80]
  • What sound did the waves of the Iapetus Ocean make, when breaking upon the shores of Laurentia at the Cambrian Pilot beach? [81]
  • (6th grade general knowledge question for people who were asleep.) What's the highest point in NC? [82] For extra points, who's been to the top of it? Who is it named after? [83]
  • How long does it take for a mineral to be transported from the active margin of a continent to the passive margin? [84]
  • What is the NC State Rock (hint: I mentioned it in the talk)? [85]
  • What do geologists find in creeks? [86]



[1] CGS 1980s Field Trip Guide Book (http://carolinageologicalsociety.org/CGS/1980s.html)

[2] "Exploring the Geology of the Carolinas" Stewart K.G. and Roberson M., 2007, ISBN-13 978-0-8078-5786-1. Chapter 18, Pilot Mountain State Park

[3] Carolina Geological Society, 50th Anniversary Edn. 1991, J. Wright Horton Jr and Victor A. Zullo Eds. University of Tennessee Press, Knoxville, TN. ISBN 0-87049-662-X

[4] not fall or winter

[5] CGS Field Notes, 1988, Forward

[6] Exploring the Geology of the Carolinas. Stewart K.G. and Roberson M., 2007, ISBN-13 978-0-8078-5786-1. Chapter 18, Pilot Mountain State Park.

[7] Mayberry (http://en.wikipedia.org/wiki/Mayberry)

[8] Saura (http://en.wikipedia.org/wiki/Saura)

[9] sign in top parking lot of Pilot Mtn Park.

[11] sign in top parking lot of Pilot Mtn Park.

[12] Exploring the Geology of the Carolinas. Stewart K.G. and Roberson M., 2007, ISBN-13 978-0-8078-5786-1. Chapter 18, Pilot Mountain State Park.

[13] Grandfather Mountain is Bird Watcher's Paradise (http://www.grandfather.com/conservation_interpretation/bird_watchers_paradise.php)

[14] Asheville Bird Watching: Top 5 Birding Locations (http://www.romanticasheville.com/birds.htm)

[15] Travel to Piedmont of North Carolina, and Flatlands of Delaware (Mar/Apr 2010) (http://www.vftt.org/forums/archive/index.php/t-35482.html)

[16] on arriving in the park, I find that rockclimbers are only allowed on some parts of the Ledge Spring Trail.

[17] GUIDE TO GEOLOGIC POINTS OF INTEREST ALONG INTERSTATE 40 (http://www.geology.enr.state.nc.us/proj_earth/I-40.htm)

[18] anticline (http://en.wikipedia.org/wiki/Anticline)

[19] Highest Elevation (ft) Locations for NC Counties (http://www.geology.enr.state.nc.us/county/county_high_points.html)

[20] Occoneechee Mountain (west summit). (At least it was in 2008.) You can take a guided tour the pyrophyllite mine there.

[21] CGS field notes 1988, p1, column 2, para 4

[22] Phil Bradley, pers. comm. 2013

[23] Sauratown Mountains) (http://en.wikipedia.org/wiki/Sauratown_Mountains)

[24] Sauratown Trail (http://en.wikipedia.org/wiki/Sauratown_Trail)

[25] Sauratown Trails Association (http://www.sauratowntrails.org/)

[26] Friends of the Mountain to Sea Trail (http://www.ncmst.org/the-trail/plan-your-hike-2/trail-sections/section-21/)

[27] Sauratown Mountains (http://en.wikipedia.org/wiki/Sauratown_Mountains)

[28] From the leaves on the trees, and from the blue sky, the fall.

[29] Hanging Rock State Park (http://en.wikipedia.org/wiki/Hanging_Rock_State_Park)

[30] where is this?

[31] GCS Field Notes: p48, 2nd column, top paragraph.

[32] monadnock (http://en.wikipedia.org/wiki/Monadnock)

[33] Kopje, Serengeti National Park, Tanzania (http://en.wikipedia.org/wiki/File:Rock_formation_(kopje).jpg)

[34] Pietra di Bismantova in the Apennines, Italy (http://en.wikipedia.org/wiki/File:Pietra_di_bismantova_castelnovo_monti.jpg)

[35] Granitic gneiss dome of Sugarloaf Mountain, Rio de Janeiro (http://en.wikipedia.org/wiki/File:PaodeAcucar.JPG)

[36] The granitic Spitzkoppe of Namibia, formed by early Cretaceous rifting and magmatism (http://en.wikipedia.org/wiki/File:2008-06-28_08-18-02_Namibia_Erongo_Usakos.JPG)

[37] A duricrust inselberg near Dori, Burkina Faso (http://en.wikipedia.org/wiki/File:De_Yalgo_a_Dori_Marco_Schmidt_0922.jpg)

[38] Exploring the Geology of the Carolinas: A Field Guide to Favorite Places from Chimney Rock to Charleston. Kevin G. Stewart and Mary-Russell Roberson (C) 2007, University of North Carolina Press, ISBN-978-0-8078-5786-1. Trip 18: Pilot Mountain State Park: Beach Sands in a Mountain.

[39] Paleogeographic Significance of teh Quartzite on Pilot Mountain, Surry County, North Carolina, Dan Walker, p55-62

[40] Phil Bradley, pers. comm.. Phil explained the minerals involved and why the cross bedding was still visible, but it was a bit over my head.

[41] Cross-bedding (https://en.wikipedia.org/wiki/Cross-bedding)

[42] p57, Depositional Setting, and photos on p58.

[43] Channeled Scablands (https://en.wikipedia.org/wiki/Channeled_Scablands)

[44] alluvial environments (http://www.searchanddiscovery.com/documents/Shell2/images/chptr3.htm)

[45] I just passed my PMP exam, in which many of the questions are based on text like this. There is an extra step; you first have to figure out what the question is asking, then you can answer the question.

[46] Hiker's Notebook (http://www.sierrapotomac.org/W_Needham/ChilhoweeGroup_060106.htm)

[47] Geologic Time Scale (http://en.wikipedia.org/wiki/Geologic_time_scale)

[48] Between 540-520Mya, the light sensitive patches on each side of the trilobite's cephalon (head) developed into segmented eyes, capable of forming images. The trilobite's neural system also had to develope to form, interpret and act on the images. This was first eye on the earth and was the forerunner of the eyes found in insects, which also have 3 body parts, and which branched from the trilobites. The trilobite presumably was the smartest thing on earth, possibly up there with locusts. The trilobites could now hunt for their prey using light. The other co-residents of the sea had to develope mechanisms to avoid being eaten. Hard shells and heavy armour (which make nice fossils) appeared for the first time, evidence of an arms race between prey and preyed. Being able to swim quickly became useful. Trilobites became the α-predator; the lion and tiger of the Cambrian sea.

[49] Active -v- Passive Margins (https://en.wikipedia.org/wiki/Passive_margin#Active_vs._passive_margins)

[50] MEA110 appendix (http://www.jeffreycreid.com/MEA110.html). The file is http://www.jeffreycreid.com/NC Through Time.PDF.

[51] Window (https://en.wikipedia.org/wiki/Window_%28geology%29)

[52] Nappe (https://en.wikipedia.org/wiki/Nappe)

[53] Klippe (https://en.wikipedia.org/wiki/Klippe)

[54] Fault Duplex Structure (http://structuralgeology.50webs.com/fault_duplex.htm)

[55] Geology duplex (http://bio-geo-terms.blogspot.com/2007/09/duplex.html)

[56] Horse (https://en.wikipedia.org/wiki/Horse_%28geology%29)

[57] What are thrusts and why are they important? (http://www.see.leeds.ac.uk/structure/assyntgeology/geology/thrusts/what/index.htm)

Duplexes and thrust sequences (http://www.see.leeds.ac.uk/structure/assyntgeology/geology/thrusts/what/duplexes.htm)

[58] Moine Thrust Belt (http://www.see.leeds.ac.uk/structure/assyntgeology/geology/thrusts/index.htm)

[59] CGS 1988 field notes, p 43, col 2, para 2.

[60] What do you mean by the term Peneplain (http://www.preservearticles.com/201101303766/what-do-you-mean-by-the-term-peneplain.html)

[61] Pediment_(geology) (https://en.wikipedia.org/wiki/Pediment_%28geology%29)

[62] CGS field notes 1988, p43 first para

CGS field notes, 1988, p52, Summary, Point 4.

[63] CGS field notes, 1988, p43, column 2, 2nd para.

[64] Hiker's Notebook (http://www.sierrapotomac.org/W_Needham/ChilhoweeGroup_060106.htm)

[65] Diastrophism (https://en.wikipedia.org/wiki/Diastrophism)

[66] Neritic Zone (https://en.wikipedia.org/wiki/Neritic_zone). The neritic zone, also called coastal waters, the coastal ocean or the sublittoral zone, is the part of the ocean extending from the low tide mark to the edge of the continental shelf.

[67] CGS field guide 1988, p43, col1, para 2.

[68] CGS field guide 1988, p46, col2, para 3. (I didn't see them, but the geological people on the field trip did.)

[69] Diamictite (https://en.wikipedia.org/wiki/Diamictite)

[70] rhododendron (note the leaves curled up from the cold).

[71] CGS field guide 1988, p57, col1, para 2

[72] https://en.wikipedia.org/wiki/File:Metamorphic_Facies.jpg metamorphism (https://en.wikipedia.org/wiki/Metamorphism)

[73] If you drop a piece of sandstone onto a rock, it smashes into many pieces. Quartzite just bounces.

[74] None.

[75] You have to be a rockclimber or a nesting raven. (This is not quite true. Rockclimbing is allowed only in parts of the Ledge Spring Trail. You aren't allowed to rockclimb the Big Pinnacle.)

[76] Nothing. They didn't survive the arrival of the Europeans and were obliterated. Few people have ever heard of them and we don't even know the language they spoke.

[77] Nothing. There's no way to differentiate them. (On arrival in the park, I find that even though the Sauratown Trail is part of the Mountain to Sea bicycle ride, that you aren't allowed to ride a bicycle on the Trail. I take it that the Mountain to Sea riders carry their bicycles for 22miles through this part of it.)

[78] Ouagadougou (I like the sound of the name.)

Geologists need to know this sort of thing. This spelling is from the French orthography. If the British had collonised the place instead, it would be spelled Wagadugu. Ouagadougou (https://en.wikipedia.org/wiki/Ouagadougou).

[79] Wave action reworks the load deposited by rivers into finer particles which are removed to deeper water. Only the larger grains of resistant material, the quartz sand is left behind. The rest is moved off-shore.

[80] One of the people in the audience said "gnarly".

Quite strong. The quartz sand has been extensively reworked.

[81] Nothing. (There was no-one to hear it.) You'd know this if you listened to Steven Wright's CDs.

One of the people in the audience asked if I knew about Stephen Wright's collection of trilobites. I asked if this was the one he kept on the floor of the oceans around the world. Apparently it is.

[82] Mt Mitchell.

[83] (from wikipedia) The mountain was named after Elisha Mitchell, a professor at the University of North Carolina, who determined its height in 1835, and fell to his death at nearby Mitchell Falls in 1857, having returned to verify his earlier measurements.

Mitchell did a lot of exploring of the state. He's well remembered by the geologists who lead the CGS trips. He must be a good guy. His field notes often refer to the difficulty, on his return to UNC from field trips, of finding a parking spot for his horses and wagons.

[84] It can take a while. Don't get caught in a subduction zone.

[85] granite. New Hampshire doesn't know what it's talking about. Our politicians wouldn't have declared it our state rock, unless everyone already identified granite with NC.

[86] Vines, thorns and fallen trees.