Metamorphism at Marshall Shore EarthCache
Metamorphism at Marshall Shore
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This little strip of land along the road on the southwest shore of Lake St. George gives you a chance better understand the processes and forces involved in metamorphism.
It is no wonder that this beautiful little strip of land has been left undeveloped. The bedrock is very close to the surface and in much of the area exposed to the elements. It would be difficult at best to develop this land with summer home so it is an excellent place for a picnic table or a place to go for a summer swim on a hot day. The ledge has been exposed near the water and just under the water giving you a good chance to see rock that has been cleaned by the water and beached by the weather yet the broken sections allow you to see what the rock originally looked like before it was exposed to the elements.
According to the Maine Geological Survey, the distinctive streaked texture of the rock is called foliation, which is caused by heat and pressure. These rocks were formed deep under ground slowly over long periods of time, giving it a twist wood grain appearance. The process that transforms the original rocks is called metamorphism. These metamorphic rocks are called gneiss, which are formed from the same materials as the local granite. The formation that these rocks are part of is called the St. George Granite Gneiss and are believed to be 420 million years old.
What I find most interesting at this location are the white streaks, which are remnants of dikes that have been squeezed, stretched and twisted during the process. Check the formation for the variation in size and texture of these veins and you will find some interesting things. These dikes were formed before the processes of metamorphism took place, which can be easily identified the way they have been deformed. It is difficult to impossible to trace the dikes as they have been so deformed. Some sections have a very unique shape.
Remember this is an earthcache so there is no container just an earth science lesson in an amazing natural area. To log this cache, you must post a photo of yourself with your GPS showing the metamorphic rocks in the background. Email me through my profile an estimate of the width of the intrusion at the posted coordinates. And the shape of the rock that has been deformed at N44 22.645 W 69 21.088. While you are here take the time to walk to the south along the shore to look at the latering of the rocks. Also make sure you checkout the rocks under water just to the north of the coordinates that are posted. The whole are is only about 100 meters long so it will not take long to explore. Please make sure to post your photo and answer the question. Please remember to include the name of the earthcache in your email.
Reference site used can be found at (visit link)
If you enjoy this earthcache you may want to check the Maine Geological Survey located at (visit link)
They have developed a number of information sheets or field localities giving a great deal of information about geologic features. They also have a number of books and maps about Maine’s natural history/ geology that you might find interesting.
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