This EarthCache will take you to Erie Land Lighthouse in Erie, Pennsylvania. Parking is available on the south side of the lighthouse. Please respect the area, and no night caching.
To log this EarthCache, post your log here (please no answers to the questions in your log!) and send us a message through geocaching.com with answers to the questions below within three days:
1) Look around the base of the structure at the limestone foundation. Of the three broad types of fossils described below (brachiopods, corals, and crinoids), which type is most prevalent?
2) What approximate percentage of the limestone is composed of visible fossils?
3) What is one specific fossil you see in the limestone (more specific than brachiopod, coral, or crinoid)?
4) Examine the blocks of sandstone that make up the structure. What approximate percentage is composed of tafoni?
5) Where are the tafoni larger and/or more prevalent? Why do you think this is?
6) (Optional) Post a picture of you and/or a personal item with the lighthouse in the background (please no spoilers!)
Erie Land Lighthouse
Image taken from visitpa.com
Erie Land Lighthouse is an historic lighthouse located on the shores of Lake Erie. The lighthouse you see today is the third construction of this lighthouse, which was the first in the Great Lakes. The first construction stood for forty years, while the second lasted less than ten years. Both were demolished due to settling foundations leading to damage and instability. After the second lighthouse was demolished, it was discovered that a layer of quicksand existed in the soil beneath the site. Consequently, the third lighthouse was moved a bit farther away from the bluff's edge, and the site was excavated to ensure a strong foundation. This foundation consisted of eight layers of solid oak timbers beneath six feet of crushed limestone set in cement. The lighthouse itself consists of 49 feet of Berea sandstone with a diameter of nineteen feet at the base and fourteen feet at the top. The diameter at the base is wider than the previous lighthouses, which also allows for increased stability. Construction was finished in 1867, and it remains standing today. taken from lighthousefriends.com
Limestone Formation
As previously mentioned, the Erie Land Lighthouse is made of Berea sandstone atop a layer of limestone. Limestone is a sedimentary rock most commonly formed in warm, shallow marine waters. It consists primarily of calcium carbonate in the form of calcite. When organisms with calcium carbonate containing shells and skeletons die in these environments, their debris accumulates on the ocean floor. Over time, these sediments are broken down and solidified together to form limestone. This origin is often evident due to the presence of visible fossils within the stone. taken from geology.com
Limestone Fossils
Fossils can be quite prevalent within limestone. There are visible fossils present in the limestone of Erie Land Lighthouse. The pictures below depict some of the fossils that can be found within limestone. They are divided into three categories: brachiopods, corals, and crinoids. These are not all inclusive, but several of these fossils can be found on the lighthouse.
Images taken from isgs.illinois.edu
Sandstone Formation
Sandstone is a type of sedimentary rock composed primarily of sand-sized (0.625mm to 2.0mm) grains of mineral, rock, or other organic material. It also contains a material that bands the sand grains together known as a cementing material. The sandstone may contain silt- or clay-sized (less than 0.625mm) particles filling in the spaces between the grains of sand. Typically, quartz makes up the largest percentage of sand grain within sandstone, and the quartz content can be up to 90% or more. Feldspar is also a common component of sandstone. Sandstone may contain larger sized grains, such as granules (2mm to 4mm), but the rock would still be classified as sandstone if the primary component is sand-sized grains.
Tafoni
Image taken from hypocentre.wordpress.com
Tafoni are small (less than 1 cm) to large (greater than 1 m) cavity features that can develop in both natural and manmade vertical to steeply sloping exposures of granular rock, such as sandstone. Subcategories of tafoni include honeycomb, stonelace, alveolar, sidewall, basal, nested, and relic tafoni. Tafoni often occur in groups and can be found in all climate types but most frequently occur in salt-rich areas, such as deserts and coastal regions. Salt weathering is believed to be the primary cause of tafoni, but the formation is widely accepted to be the result of a complex interaction of physical and chemical weathering involving processes such as salt weathering as well as cyclical wetting and drying. Tafoni are found in areas where salt is not prevalent (such as this area), so there must be other forces at work. taken from wikipedia.org
