Welcome to the southwestern most part of Delaware. It is marked by the southernmost Mason-Dixon marker, first monumented by surveyors Mason and Dixon in 1764. In fact, it was here where they began thier survey that would later become known as the Mason-Dixon line. The Mason-Dixon line endded the nealry century long despute for land claims betwen William Penn and Lord Calvert, now Pennsylvania and Maryland respectively. While the current line deviates some from what was originally planned, limited by the tools and the technology of the colonial times, it was incredible that the line is almost perfect.
Mason and Dixon set stones every mile north from this stone until it had reached a tangent to the twelve mile circle in northern Delaware. At this point, the border would have went along this circle until it reached the 40th parallel where the border would have went due west along this line. The Twelve Mile Circle is a circle with its center at the New Castle Courthouse in downtown New Castle, Delaware where its radius is 12 miles. Because of the limitations of the time, the surveyed line does not actually tangent the twelve mile circle. Instead, it runs slightly to the west. This created problems of who owned what land in a small 800 acre pack of land known as The Wedge (shown in red below). The US supreme court had a say in the matter in the early 1900s and by 1921, Maryland, Pennsylvania, and Delaware agreed that the land should be granted to Delaware.
The stone at the above coordinates is called the Middle Point Mason-Dixon stone because it makes a right angle with the Transpennisular line, a line to mark the southern border of what was then the lower three counties of Pennsylvania. The Transpennisular Line cuts the Delmarva penninsula in half, and the Mason-Dixon line cuts that line in half. This stone, the one at the above coordinates, marks the center of the Transpennisular line and the southern most point of the Mason-Dixon line. The Transpennisular line is not part of the Mason-Dixon line, and is its own separate entity.
Now for the Geology!
All of the original Mason-Dixon (around 300) are placed at 1 mile intervals from one another. Every five miles they places special "crownstones" because of the crown on the crest of Lord Baltimore. Each stone, most weighing more than 500 lbs and stood anywhere from 3 1/2 feet to 5 feet in height before being set. They were quarried in England, specifically on the Isle of Portland (red circle in the map below) in the English Channel, and are made of limestone. More specificly the limestone is called Portland Stone (photo of a Portland Stone quarry below), which formed during the Late Jurrasic period about 152 to 145 million yeras ago. Dinosaurs were already well established by this time, and had another 90 million years left until they went extinct. Limestone is still being quarried from the Isle to this day, some 250 years later.
Limestone is a calcium carbonate sedimentary rock formed in a warm, shallow marine sea environment. Sea shells are rich in calcium carbonate. When sea animals that have sea shells die, they accumulate on the ocean floor. Over time, these shells are crushed and compacted by the layers above. Sometimes, however, under the right conditions the original structure of the shells can be preserved in the rock. These are what we would call fossils. Not all limestone is fossiliferous, but some are.
Limestone is a relatively soft rock (compared to other sedimentary rocks) which is why it was chosen to be the stone of choice to mark the Mason-Dixon Line. It has the added benifit of being able to be easily molded and fabricated to the desired specifications. This included carving an "M" for Maryland and a "P" for Pennsylvnia. Note when the survey was being conducted, Delaware did not exist yet. The three counties of Delaware were part of Pennsylvania, hence why the original stones never mention Delaware. In addition, carving the crests of each of the crownstones were made easier due to softness of the limestone. Image below shows the Calvert (Lord Baltimore) crownstone, on the Maryland side of this Mason Dixon marker.
However, there is one downside that was not accounted for. Limestone is very supseptible to weathering. There are two main types of weathering: mecanical and chemical. Mechanical weathering occurs by physically breaking up the rock as opposed to chemically breaking down the rock. An example of mechanical weathering includes frost weathering. During the winter months, ice can form within microscopic cracks and fractures within the rock. As ice expands from a liquid to a solid (one of the only substances to do so), it can cause cracks and fracture to grow, breaking up the stone from the inside out. A simple diagram below shows how frost wedging can physically weather a rock. Mechanical weathering tends to leave behind noticable cracks, unlike chemical weathering. Chemical weathering tends to smooth the rock of its rough edges, especially around any man-made carvings or engravings.
An example of chemical weathering includes rain. Rain water is slightly acidic, with am average pH betwen 5.0 and 5.5. pH measure the disolved H+ ions in solution. In essence, it measures the accidity of a solution based on its disolved hydrogen content. The scale is logmaritic, meaning 5.1 is 10 times greater than 5.0. The pH scale goes from 0 (being a true acid) to 14 (being a true base). Pure water has a defined pH of 7. However, natural water typically contains disolved minerals and impurities in it which can make it more acidic or basic. When water evaporates naturally, it tends to have more H+ ions then in a liquid state. This means that when it condences into rain, it tends to be more acidic. This can be problematic for limestone as the calcium carbonate within the rock will chemically react with the rain. The acidic rain will disolved the calcium carbonate in the rock. overtime, the rock will degrade away. Since the industrial revolution, rain has become more acidic. As we pollute our atmosphere toxic gases such as SO2 (sulfur dioxide) can react with the rain to make them even more acidic which exacerbates the problem. SO2 creates sulfuric acid, which can eat (disolve) away at anything from limestone to plants.
As previously mentioned, edges have a higher surface area than faces of a carved stone. If a stone has any carvings such as an "M", "P", or even a crest, these tend to weather at a faster rate than the rest of the stone. You can see this well in the black and white photograph of a Mason-Dixon marker above. To prevent this, a shelter or cover can be built. However, because there are over 300 stones building a shelter for each one would be impractial. That is why a shelter was built for this specific Mid-Point stone because if its historical importance.
Since the original survey, some original Mason-Dixon stones set in the 1760s have been destroyed (either naturally or by humans) or burried by natural forces such as floods, landslides, or simple movement of sediments over hundreds of years. A handful of the original stones have never been recoved. Some of the ones that have been recovered had to have been dug up from the ground. The Middle Point stone, however, has been left relatively undamaged since 1764. The current enclosure that covers the markers were built in 1962 by the Daughters of the American Revolution. Below is a photo taken in 1976 of the enclosure. There have been a few additons since then, including a full gated enclosure preventing people from vandalzing the markers.
When you look at the middle point Mason-Dixon stone (the largest of the stone within the enclosure) you will notice three other stones. These stones were earlier attempts at marking the middle point along the transpennisular line and pre-date the attempt by Mason and Dixon. This link gives an exceptional explaination of each of the stones found withint the enclosure, if you are currious as to the history of each one. I will say a quick note about one of them. The smallest of the stones (the one that lies inbetween the other two stones that are not the Mason-Dixon stone) was found by a local farmer and its origin is unknown. Each of these three smaller stones were set nearby and later moved to the enclosure to protect them from further weathering.
Today, the Middle Point Mason-Dixon marker is part of the Delaware Boundary Stones Historic District, which is listed on the National Register of Historic Places. This specific stone is a contributing object to the district. The district it composed of several stones from the Transpeninsular Line and the north/south portion of the Mason-Dixon line whish defines Delaware's western border. If you are interested in the history of these stones within the NRHP district, you can read about them (and their exact locations) on the National Register nomination form. Once you click this link, you can then click, "Download this PDF" to view the nomination form if you so desire.
Works Cited
https://www.inquirer.com/philly/opinion/20160524_Commentary__Preserving_Mason-Dixon_s_milestones__history.html
https://en.wikipedia.org/wiki/Isle_of_Portland
https://en.wikipedia.org/wiki/Transpeninsular_Line
https://en.wikipedia.org/wiki/Twelve-Mile_Circle
https://en.wikipedia.org/wiki/Wedge_(border)
https://en.wikipedia.org/wiki/Mason%E2%80%93Dixon_line
https://en.wikipedia.org/wiki/Portland_stone
https://storymaps.arcgis.com/stories/008e87f0604943c1b6d9fae57046d920
https://opengeology.org/textbook/5-weathering-erosion-and-sedimentary-rocks/
https://www.epa.gov/acidrain/what-acid-rain
https://npgallery.nps.gov/AssetDetail/NRIS/75002101
TO LOG A FIND ON THIS CACHE YOU MUST ANSWER THE FOLLOWING QUESTIONS. RESPONSES CAN BE SENT THROUGH MY EMAIL OR THE GEOCACHING MESSAGE CENTER ON MY PROFILE PAGE. ANY INCORRECT ANSWERS WILL RESULT IN A FOLLOW UP MESSAGE FROM ME. ONCE YOU SEND YOUR EMAIL/MESSAGE, YOU ARE FREE TO LOG THIS CACHE.
1. "Middle Point Mason-Dixon Marker" on the first line of your email/message AND list all geocaching names of your party so I can match your answers to them. If you all want to learn something, I would prefer each cacher send me individual emails/messages in the spirt of earthcaching.
2. Take a photo of you (or your signature item if you don't want to show your face) with the enclosure behind you (or your signature item). Be sure not to show any close up photo of the stone in your images. Please upload these images with your found it log. Do not message me any photos.
3. Compare the Mason Dixon marker to the other three stones within the enclosure. Which one of the four is most weathered? Why do you think that the case? If you need help identifying which stone is which, you can use this link here and scroll down until you see the info about the Middle Point Marker.
4. Looking only at the Mason-Dixon stone, which type of weathering (chemical or mechanical) has had a bigger effect on this stone? How can you tell? Explain your reasoning based on your own observations and what you learned in the cache description.
5. Do you see any evidence of fossils within the Mason-Dixon stone? Why do you think this is the case?
6. What additional steps do you think, if any, could be made to prevent further weathering of these historic stones?
