All art is but an imitation of nature
Omnis ars naturae imitatio est, in Epistulae Morales ad Lucilium
-Seneca the Younger (4 BC - 65 AD)
When you reach the listed coordinates, you will see a free-standing rock that is a masterpiece of nature. More than 2,000 years ago, the Roman philosopher Seneca the Younger wrote that all art is but an imitation of nature. Excavated during work on the Outer Loop Road at the Blandy Experimental Farm around 2010, the beauty of this rock was instantly recognized. Earthcaches are designed to teach about the history of our planet, but the pure beauty of geology isn't lost on the geologist or the Earthcacher. The geologist sees the beauty and looks beyond to understand the rock's history, a skill that geocachers can learn from Earthcaches.
First, the formalities: Permission for this Earthcache was generously provided by the Blandy Experimental Farm, site of the State Arboretum of Virginia. The grounds are open from dawn to dusk 365 days a year and there is no charge for admission. Absolutely no night caching allowed! Do not climb on or attempt to sample (with a hammer, pick or other device) this rock. Please do not post pictures of the rock in your log, so as to leave the surprise for others.
Optional: In your log, describe what you thought of this rock when you first saw it.
Let's see what we can learn about the history of this rock. Before the rock was buried, it was sculpted into its current shape. If you examine the two large, vertical faces of this rock, one is heavily sculpted, while the other shows little sculpting. These two surfaces are the "top" and "bottom" of the rock at the time of sculpting. Let's figure out which is which. Rocks are typically sculpted by one of three forces - humans, wind, or water.
Humans - Stone sculptures have been produced from all types of rocks throughout human history, but most sculptures are made of durable rocks without layering or fractures. Marble has been the stone of choice since the time of Seneca the Younger. The background image for this cache is a marble bust of Seneca the Younger.
Wind - Rocks sculpted by wind are called ventifacts. These can take a variety of shapes, but are typically sculpted on multiple sides. Ventifacts form in arid environments, where dry soil and little vegetation allows wind to move particles of rock, soil, or ice. The ventifact above is from Antarctica, the driest continent on Earth.
Water - Sediment carried by water can erode the rocks over which it flows, but only on the surface exposed to the flowing water. The most distinctive feature of water-shaped rocks are potholes, where small rocks carried by swirling water carve a hole in solid rock.
Question 1: Looking at the rock, do you think the shape was sculpted by humans, wind or water? Why do you think this? Based on your answer, which of the two surfaces (facing the buildings or facing the fields) was the top at the time of sculpting?
Before the rock was sculpted, sedimentary layering that you see in the rock was formed. We know this because the layers of rock occur on each side of the sculpting, so they must have formed earlier. The rock is a piece of the Conococheague Formation, formed during the Cambrian period more than 500 million years ago. The Conococheague is more than 2000 feet thick and consists of repeating types of rock every 20-30 feet (Root, 1965). In some parts of the Conococheague, stromatolites - mounds formed by algae - are found. To learn more about these, visit GC8H2ZC. This rock consists of interlaminated white limestone (CaCO3) and gray dolomite (CaMg(CO3)2).
The individual layers here were deposited in water - long before the sculpting that occurred much later. We can get some idea of what that ancient water was like. For more than a century, geologists have wondered why dolomite is so common in ancient rocks, but not found in modern environments. Recent studies by scientists from the Univ. of Wisconsin (Fang and Xu, 2018) on rocks from Central Pennsylvania similar to this rock show that mats of algae occurred in this water. The gray dolomite layers are rich in organics from this algae. Today, algae mats of this type are only present in a few rare environments, like Shark Bay, Western Australia, where salt rich waters prevent animal grazing.
Question 2: How thick are the individual layers of limestone and dolomite - thinner than the width of one finger, about the width of 2-3 fingers, or thicker than the width of your hand? Which is more abundant - white limestone or gray dolomite?
We also know that the water was moving. If you look carefully at the layers exposed on edge (like looking at the side of deck of cards), you'll see that they aren't straight, but have upward convex shapes likely formed by a combination of mounds of algae growth and water flow, causing ripple-like features. The direction of the upward convex mounds point to the "top" direction when the ancient water and algae was present. To a geologist, if the "top" when the layers formed doesn't match the "top" when the rock was later sculpted, then the rock was turned upside down ("overturned") between when the ancient layers formed the rock and when the rock was later sculpted. This often happens during mountain building - which has occurred many times in the last 1/2 billion years in what is today Virginia. If the two "top" directions match, then the rocks haven't been overturned.
Question 3: Based on the Earthcache lesson and your observations, do you think mountain building overturned this rock during its history? Explain your answer.
After appreciating the beauty of this rock, you hopefully have a deeper appreciation of how a few simple observations can tell you about the history of an individual rock - even one dug up during road construction.
Logging Requirements
After reading the information above, send answers to questions 1-3 to the cache owner:
Question 1: Looking at the rock, do you think the shape was sculpted by humans, wind or water? Why do you think this? Based on your answer, which of the two surfaces (facing the buildings or facing the fields) was the top at the time of sculpting?
Question 2: How thick are the individual layers of limestone and dolomite - thinner than the width of one finger, about the width of 2-3 fingers, or thicker than the width of your hand? Which is more abundant - white limestone or gray dolomite?
Question 3: Based on the Earthcache lesson and your observations, do you think mountain building overturned this rock during its history? Explain your answer.
WITH YOUR LOG, POST A PHOTO. Posting a photo that readily indicates that you (and anyone else logging the find) were at the location. You do not have to show your face, but the photo should include you or a personal item. Please do not show any answers to any of the questions above. NOTE: Per newly published Earthcache regulations, this is required to claim the find.
If responses to the questions above are not received in a reasonable time period, cachers will receive a request for answers. Failure to respond may result in deletion of your log.
REFERENCE
Fang Y. and Xu H. (2018) Study of an Ordovician carbonate with alternating dolomite-calcite laminations and its implication for catalytic effects of microbes on the formation of sedimentary dolomite. Journal of Sedimentary Research, 88, 679-695.
Root S.I. (1965) Cyclicity of the Conococheague Formation. Proceedings of the Pennsylvania Academy of Science 38, 157-160.
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