You are in the parking lot for the Russell-Rufty Memorial
Shelter.
The Shelter, incidentally, houses the Veterans’ Memorial Room,
conference room, office and meeting hall for the Gold Hill Mines
Historic Park, as well as many photos and other informative items
about the area.
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In his doctoral dissertation, Jeffrey Pollock
stated the following: "The Floyd Church Formation comprises
medium- to thick-bedded epiclastic mudstone." This technical
statement has important meaning for Gold Hill and Rowan County, so
let's decipher it: A "formation" is a rock unit that can be
mapped on a geological map, and which has an upper and lower limit.
That means you can look at the rocks in the countryside
occupied by the Floyd Church Formation and see the same type of
rocks everywhere, until you see something quite different,
signaling that you're now in another formation. Early
geologists noted a particular rock type in the vicinity of the
Floyd Baptist Church on its namesake road near Lexington, NC, and
called the rock unit the Floyd Church Formation. If you go
anywhere between Asheboro, Denton, Gold Hill and Albemarle, and
find the same kind of rocks, you're looking at Floyd Church
Formation rocks
So, just what are these rocks? They are epiclastic mudstone,
according to Dr. Pollock's description. The term "clast"
refers to pieces of rock and mineral, while "epi" denotes the fact
that these fragments originated over or beyond the place where they
were laid down. Mudstone is a fine-grained sedimentary rock
composed of mostly bits of clay or mud. The size of the tiny
grains making up the "mud" in mudstone is technically important to
geologists, as it determines what the rock will be called, as well
as many of the rock’s characteristics. Mud has a grain size
of only up to 0.0025 inch (0.0625 mm), so the individual grains are
much too small to be seen without a microscope.
"Bedded" refers to how smoothly these trillions of tiny grains
were laid down. Because the beds are described as "medium- to
thick-bedded", the grains were deposited quite uniformly over a
long period of time -- millions of years, in fact. Such a
deposit history means that the area was well under the sea, and not
in an above ground or tidal area. The period of deposit was roughly
25 million years, and it was centered on approximately 540 million
years ago.
Yes, I can hear you say "Big woop, a bunch of mud rocks.
So what?" Bear with me, as those rocks are going to
change – and here's where the magic begins to happen.
Over the millions of years that the grains were piling up on the
ocean floor, they got thicker and thicker, and both heat and
pressure began to increase in the lower parts of the deposits.
This began to harden and compress the grains and turn them
into consolidated rock. Remember, it was a constant process
-- a lot can happen over millions of years!
A more abrupt and dramatic change took place during the time
that the continents of what are now Africa and South America
collided with what we now call North America. This colossal
process pushed up the Appalachians to be one of the great mountain
ranges on the planet -- probably on a par with today's Himalaya
Mountains. While impressive mountains were thrust up to the west,
the fate of the mudstones we're concerned with wasn't nearly so
dramatic. In fact, they were buried, and subjected to more
heat and pressure than anything they had experienced before.
This changed the rock slightly, as it made what had been
seafloor, fairly soft rock, into a pretty hard rock -- more
magic.
Eventually, the supercontinent created by the collision
described above began to break up, and the Atlantic Ocean was born
between them (much like today's Red Sea, but on a much larger
scale). So, where are those huge mountains? The
Appalachians today are simply the eroded remnants of those
monstrous peaks, and that wasn't the only place erosion was taking
place. Everything above ground, all the way to the shore
line, was eroding. As billions of tons of rock and mineral were
eroded and carried away by the rivers and streams of the past, the
land rose. Continents actually "float" on denser material,
and when weight is removed from them, they "bob" upward.
The rocks first described around the Floyd Baptist Church well
over 150 years ago have risen from miles deep within the earth, and
the rocks that were above them are now in the Atlantic Ocean,
building new mudstones. More magic, indeed.
All the above brings us to where we are standing. There is
an immense quarry operation on Old Beatty Ford Road, just to the
south of where you are. Huge rocks are brought out from a very
large open pit, and are then crushed, graded, and cleaned to meet
customer specifications. Six to twelve railroad cars are
removed at least 2-3 times a week and replaced with empty cars to
be loaded. Dozens, if not hundreds, of trucks a day take loads of
that crushed, cleaned and graded rock out to building sites,
asphalt plants, and other end-users -- including the Historic Gold
Hill and Mines Foundation, Inc., on whose Floyd Church Formation
crushed rock you are now standing.
It is ironic that lowly mud grains at the bottom of an ancient
sea have become, by far, the most economically important rock ever
to be mined or quarried at Gold Hill. This is a geological magic
trick that has taken over a half a billion years to unfold.
Logging Questions:
Send me an e-mail – not part of your log – responding to the
following:
1. Make the subject of the e-mail
“GC1Y1KE, Gold Hill: Mudstone Magic”
2. How many people were in your
party?
3. Post a picture of you and your party,
and try to include some of the stones in the picture.
4. When Africa and South America
collided with North America, the mudstones were slightly changed.
Some geologists insist that the correct term for the rock should be
"metamudstone". What's the difference between mudstone and
metamudstone, and which term do you think should be applied to the
rocks quarried in Gold Hill?
5. Some uses of the crushed stone
produced at Gold Hill were mentioned (asphalt and building site
underlayment) in the text. What is at least one other use of
crushed rock?
6. Look closely at the stones, and try
to describe them for me. Do they contain large, obvious minerals,
or do they seem to be just a mass of no obvious pieces or parts?
This is the nub of the questions: Why do you suppose you see what
you see?
7. Extra (fun) credit: Can you find any
that are the typical bluish-grey, but have a layer of tan-colored
stone in them? If you can, you are very lucky. Can you tell me what
could have formed that tan-colored layer?
Bibliography:
The author thanks Phil Bradley, Senior Geologist, North Carolina
Geological Survey, for his valuable corrections, additions and
suggestions relative to this write-up. Any mistakes herein,
however, are solely the responsibility of the author. 2009
The author thanks Vivian Hopkins, Vice President, The Historic
Gold Hill and Mines Foundation, Inc., and Chair of the Foundation's
History Committee. She has been a tour guide, source of knowledge,
and careful fact checker for the author.
Hibbard, J, et al. The Heart of Carolinia: Stratigraphic and
Tectonic Studies in the Carolina Terrane of Central North Carolina.
Field guide for a pre-meeting field trip of the Southeastern
Section, Geological Society of America meeting, 2008.
Pollock, J. The Neoproterozoic-Early Paleozoic Tectonic
Evolution of the Peri-Gondwanan Margin of the Appalachian Orogen:
An Integrated Geochronolocial, Geochemical and Isotopic Study from
North Carolina and Newfoundland. Unpublished PhD Thesis, North
Carolina State University, 2007.
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