Marblehead has many interesting features. One that may be overlooked is the abundance of fossils in the rocks here.
Most of the peninsula is made of Columbus limestone which is very durable so it is resistant to erosion from the lake. Columbus limestone was formed during the Middle Devonian Period around 400 million years ago. At that time this region was near the equator and covered by a shallow sea. The rock formed as sediment was compressed at the bottom of the sea. The fossils here are of organisms that lived at that time.
The geologic map above of the Sandusky area shows the extent of Columbus Limestone labeled as "Dc"
The majority of fossils here are brachiopods and corals. Brachiopods appear as similar to clam shells. They are sea animals with hard shells that were hinged at the rear. Corals look more like clusters of tubes. They were colonies of sea animals that lived together in connected modules. Some are singular circles. You might even find other fossils of plants or animals here.
Fossils around The Great Lakes are primarily found in sedimentary rock, which is formed on the Earth's surface. Layers of sedimentary rock are formed by accumulating particles like sand or silt and compressed by the weight of the layers above. Organisms within the sand and silt can form fossils.
The four main types of fossils are:
Mold Fossils; fossilized impression made in the rock as a negative image of the organism
Cast Fossils; formed when a mold is filled in
Trace Fossils; fossilized footprints, tracks, burrows, nests or other fossilized evidence left by organisms.
True Form Fossils; fossils of the actual animal or animal part
Logging Requirements
To get credit for this EarthCache, please provide answers to the following questions in a geocache message or email within seven days of your visit. Please do not post your answers in your log.
1. Pick a fossil that you find interesting. Post a picture of it with yourself or your GPS or a personal object. You may also send this picture in your message if you prefer not to post it in your log.
2. Describe the fossil in your picture. What organism was it? Do you think it is a cast, a mold or other type of fossil? How big is it?
3. How do you think the rocks here were formed?
Most of the best fossils are in the rocks closest to the lake but there are several in the boulders next to the grass near the lighthouse. Keep safe and stay off of the rocks during unsafe conditions. I have also added a waypoint for one you can see near the paved path (Fossil stop 4). Obey all State Park rule. This EarthCache has been placed with park permission.
Enjoy your fossil hunt! Favorite Points for this EarthCache are appreciated.
You may log the EarthCache find before or after sending the answers to the questions. The questions are not hard, but do require some thought and observation and are required. You must visit the site to log the find. Answers sent for a group are welcome but everyone claiming the EarthCache must be present and their fossil picture is required.
Sources
Ohio Department Of Natural Resources (ohiodnr.gov/)
USGS web site (https://ngmdb.usgs.gov/Geolex/)
Wikipedia (https://www.wikipedia.org/), (https://en.wikipedia.org/)
Ohio History Central (ohiohistorycentral.org/)