*****Congrats to miatabug for First To Find!******

This earthcache is located in the Jefferson National Forest on the border of Grayson and Wythe counties in southwest Virginia, US.  To access the coordinates, please park at the entrance to National Forest Road 57 at US Highway 21 (it is a gravel road that turns off of paved Highway 21 - you'll see a sign for Comers Rock and Hale Lake).  You'll need to walk a short distance down the road to the trailhead for the Iron Mountain Trail on the opposite side of 21 from the parking coordinates.  PLEASE be careful crossing Highway 21!  The actual earthcache coordinates are a very short walk into the woods after starting at the trailhead at Highway 21.  To get credit for visiting the earthcache site, please send an e-mail with the answers to the questions listed at the bottom of the description.

Iron Shale

Geologists recognize three main classifications of rock according to how they are formed:  igneous, metamorphic, and sedimentary.  Igneous rocks are formed by magma, or molten rock, under the earth's surface (example: granite) or when magma comes to the surface (known as lava, example: basalt).   Metamorphic rock is formed from either igneous or sedimentary rock by pressure and heat to become a different type of rock (example: gneiss).  This earthcache focuses on the third and one of the most common types of rock - sedimentary.

Sedimentary rock is formed from small pieces of other rocks that have been "glued" together.  Various types of weathering by wind, water, and chemical weathering cause other rocks to break down into small particles known as sediments.  These sediments end up getting buried and then pressure and heat (just the right amount!) work on them to compact them into new stones.  Due to the different types of weathering that create the sediments that sedimentary rocks are made of, sedimentary rocks are further classified into two different classes: detrital and chemical.  Detrital sedimentary rocks are made up of chunks of other rocks.  One particular example of detrital sedimentary rock that can be found here is shale.  

Shale is a type of sedimentary stone that is formed in clear, quiet water from clay sediment at the bottom of the water and is known as a “mudstone”.  Shale tends to break into flat pieces that are layered just as the layers of sediment were formed under the water.  Shale is also smooth because it is made up from clay or very small particles smaller than sand.  Shale is also brittle and decays easily so it is found in piles of broken pieces when it has been exposed to the elements.  So, how did shale, a sedimentary stone that was formed at the bottom of water end up here in the mountains?  Well, the answer isn't so simple.  The Appalachian mountains where you are standing at this point have a long, varied history.

Appalachian Mountain Geology

The Appalachian mountains are very old.  Geologists have studied them thoroughly over the past century and have a theory as to how they formed.  The vast majority of the Appalachians are made of sedimentary rock.  They are thought to have begun forming during the Paleozoic era, from some 250 to 700 million years ago.  The initial base rock was thrust up during the Alleghanian Orogeny 680 million years ago. During this event the ocean crust was subducted beneath the continent that is now known as North America.  Later, (approximately 540 million years ago) the North American plate split apart.  This caused inland seas to form in the areas where this shale is located and to the west and north.   It is believed that this shale was formed under this inland sea approximately 480 to 500 million years ago (Ordovician through Cambrian periods) from rivers and streams bringing sediments from the eroded Alleghanian mountains to the sea.  Meanwhile, what is now Africa was slowly drifting closer to North America.  It eventually collided with North America in a major collision (270 million years ago) and caused the sedimentary rock to be “shoved up” over the younger rock and form the Appalachians we see today. 

Iron Shale

So why is this earthcache called “Iron Shale”?  Interestingly, this region of Virginia has a history reaching back before the Revolutionary War of providing iron.  Pig iron was produced in this area using local deposits of iron ore and limestone for flux (both are sedimentary rock) in small furnaces  (see the National Forest Service link http://www.fs.usda.gov/detail/gwj/learning/history-culture/?cid=FSBDEV3_000460 for more information).   Although geologists are still uncertain how the large amounts of iron got deposited here, it is known that red, yellow and purple colors in some rocks come from oxidized iron.  For iron to be oxidized there needs to be a large amount of oxygen in the water.  This means the water had to be a river, or flood plain, or very shallow sea.  This particular area where this shale is located is thought to have been on the edge of the inland sea, so might have been in very shallow water.  Another source of iron could have been from deep sea vents that may have existed in the region during the inland sea era.

Shale deposit containing large amounts of iron – note the iron oxide (rust color and green color) 

Strip mining was common in this region during the pig iron boom– where the top layers of soils were removed to expose the sedimentary bedrock containing the iron ore.  Trees were felled to make charcoal for the furnaces and to clear cart paths for the mules to carry the ore to the furnaces.   Large areas of forests were cleared.   Large scars were made on the earth due to iron making activity in the area that can still be seen today, centuries later.   This earthcache is located at an area that was believed to be an old iron strip mine for the “Dry Run” furnace in Wythe County, VA.   Since the area has been under the protection of the National Forest Service, nature has made progress recovering itself despite the scars upon the land.

To log your visit, please e-mail me the answers to the following questions:   1. What colors do you see predominantly in the shale located here?  2. Do you believe there is iron in the rock?  Why or why not? (hint – look at the colors in the rock)   3. Do you see layers in the rock? 4. What is the elevation at the coordinates? 

Although you do not need to post a picture for credit, please feel free to do so if desired.

Please do not post answers to the questions in your log or your log will be deleted!

Thanks for visiting, and don’t forget to visit Rockden & Gemstone’s  nearby traditional cache (GCGEC6) as well as the other traditional caches and earthcaches in Jefferson National Forest.

I am a proud

References

• http://pubs.usgs.gov/gip/birth/birth.pdf
• http://www.fs.usda.gov/detail/gwj/learning/history-culture/?cid=FSBDEV3_000460
• http://www.pitt.edu/~cejones/GeoImages/5SedimentaryRocks/ClasticSedRocks/MudstonesShales1.html
• http://csmres.jmu.edu/geollab/vageol/vahist/index.html