Jan 10 Edisto Beach State Park

 

Oysters

Our visit to Edisto Beach State Park is a first time visit. There is a beach. It is adjacent to the town of Edisto Beach. There are lots of beaches around here. That was not our focus. I wanted to see the 4000 year old oyster shell midden. We had to walk 7 miles to do that but also learned about Alexander Bache and coastal survey as a bonus.

Grape vine

I have never heard of this guy before. Alexander Dallas Bache was a brilliant guy. Being the great grandson of Benjamin Franklin may have had something to do with that. After graduating from West Point and serving in the army, he went on to head the US Coastal Survey. His invention, the Bar of Invariable Length was used  to make surveying more accurate. In 1849 surveying was a tedious job. Mapping the US coast was needed for military and shipping concerns. Bache headed up this effort. On Edisto Island he contracted with a local planation to cut a "straight as an arrow", road, 7 miles long. This is known as establishing the baseline of a survey triangle. Surveying then and today is all about trigonometry and triangulation. Bache's "bar" was made of two rods of different metals. Since metals shrink and expand with temperature changes, Bache chose two metals that cancelled each other out. Thus he now had a long rod or bar of invariable length that could be used to survey that 7 mile long road. Using tripods, the long bar was leapfrogged from one end to the other. Stone monuments marked either end. Under the monument was a brass bolt that marked the exact point. In the 1990s a gps survey was conducted to test the accuracy of Bache's measurement. He was off by less than 2 1/2 inches.

A couple points of trivia here. Bache was the the first president of the US National Academy of Science. He was the first person to hire a woman for a scientific position. And he roomed with a president at West Point, Jefferson Davis. 

Bache monument west end of baseline

Along one of the creeks in the state park, is this Native American midden. It dates back 4000 years. Although, mostly oyster shells, it also has fish, bird and animal bones and broken pottery. The midden is only a small fraction of its original side. The creek has been eroding the mound.