This is an Earthcache – as such, there is no physical cache. Instead after examining the Pennsylvania Bluestone at the posted coordinates you will answer 3 questions and message me the answers. This earthache is located in a Prince William County Park with permission and night caching is strictly forbidden.
Located between the Prince William Parkway and James J. McCoart Administration Building, the Liberty Memorial was dedicated on May 9, 2006, to honor those who died on 9/11. Each of the elements that you see here has much thought and meaning to them. The flag pole belonged to a Prince William County resident who was killed during the attack on the Pentagon. The single stone to the left of that plaque is an original limestone block from the collapsed portion of the Pentagon. The shape of the reflecting pool and walkway recall the 184 lost at the Pentagon. Etched into the sides of the reflecting pool are the names of those from Prince William County who died in the attacks that fateful day, and the two columns of water represent the 2,749 lost at the World Trade Center in New York City. One thing that you may not notice is that the stone that encircles the fountain is Pennsylvania Bluestone, which was chosen as a tribute to the 40 passengers of United Airlines Flight 93 that crashed in Pennsylvania.
BLUESTONE
Bluestone from Pennsylvania and New York is sandstone that formed around 400 million years ago in the Devonian Period. It a sedementary rock that is defined as feldspathic greywacke. Millions of years ago there were myriad rivers that drained into a sea. Over millions or more years, the seascape changed as these oceans began to recede and rivers changed their course. While this was happening life forms where carried away to where Pennsylvania is today. These life forms were piled amongst other debris that eventually sank to the bottom, and fossilized as layers and layers built up. These layers turned into sedimentary rock and became what is now known as bluestone. This occurred specifically where the shallow rivers drained into the sea.
In order to discuss bluestone, we first need to talk about flagstone. Flagstone is a flat sedimentary stone with fissile bedding planes.
A fissile rock tends to break along sheet-like planes that are nearly parallel to the bedding planes. Fissility is caused by the tendency of clay minerals to be deposited with their sheet structures parallel to the depositional surface. It is naturally split into layers according to these planes and used for a variety of purposes, such as patios and pool decks, roofing, facades, and walkways. In the thirteenth century, Europeans began using flagstone for floors, walls, and ceilings. It was especially popular for the interior rooms of castles. Flagstone is bound together by minerals such as calcite, silica, and iron oxide. These internal materials are the cause of flagstone’s beautiful colors, one of which is a stunning blue leading to the name “bluestone”. The word flagstone stems from the Middle English word “flagge,” which means turf.
RIPPLE MARKS
Ripple marks are sedimentary structures (i.e. bedforms of the lower flow regime, mostly in sandy bottoms) and indicate agitation by water (currents or waves) or wind. They indicate the presence of a current at the time of sediment deposition in the rock record
Asymmetrical ripples have a long side and a short side, as seen in cross-section. Symmetrical ripples are more or less evenly shaped in cross-section view. Asymmetrical ripples form in a one-direction current by wind or water. Symmetrical ripples for in a back-and-forth, two-direction current in very shallow water by wave action.
A: Symmetrical ripple marks (also called wave-formed or bidirectional) are produced by waves or oscillating water. They have almost sinusoidal profile. These ripple marks indicate an environment with weak currents where water motion is dominated by wave oscillations (sand grains are moving in both directions, forward and backward).
B: Asymmetrical ripple marks (also called current or unidirectional) are asymmetrical in profile, with a gentle up-current slope and a steeper down-current slope. Because of this unique geometry, asymmetrical ripples in the rock record may be used to determine ancient current directions or paleocurrent directions. These ripple marks are formed in fluvial and aeolian depositional environments (sand grains are moving only in one direction).
REFERENCES:
1. PRINCE WILLIAM COUNTY'S MEMORIALS, website, pwcgov.org
2. Pennsylvania Building Stones, Parts 1 & 5, R. W. Stone, Vol. XLIX, No. 1, January 1928, pp. 34-35, & February, 1928, No. 2, pp. 109-110 quarriesandbeyond.org
3. Bluestone in Pike County, Pennsylvania, Pennsylvania Geology, W. D. Sevon, The Pennsylvania Geological Survey, Volume 9/3, June 1978, elibrary.dcnr.pa.gov 4. Susquehanna County: The Heart of Pennsylvania Bluestone, website, susqco.com
5. Everything You Need to Know About Pennsylvania Bluestone, website, woodwardlandscapesupply.com
LOGGING REQUIREMENTS:
To log this Earthcache: Read the geology lesson above. Answer all three questions posted below. Answers can be sent via e-mail or messenger contacts on my Geocaching profile. Do not post the answers to the questions in your logs.
QUESTION 1. Do you see any signs of fissile layers flaking or breaking off? (there are sections you can see the sides near the grass.)
QUESTION 2. What are some of the textural differences between the sedementary bluestone tiles around the fountain compared to that of the sedementary Indiana Limestone block from the Pentagon?
QUESTION 3. Observe areas of the bluestone with ripples. Do they appear to be asymmetrical or symmetrical?
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