Maine's Blue Clay EarthCache
Hidden : 11/26/2007
Difficulty:
3.5 out of 5
Terrain:
3.5 out of 5

Size: Size: other (other)

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Geocache Description:

This earthcache will bring you to a location where during the glacial period the waters were more like the waters of the Arctic and now had many of the extremely cold environment organisms of today’s Arctic fossilized in the glacial clay.

The story of this area begins with the glacial retreat. The last glacial episode in Maine began about 25,000 years ago, when the Laurentide ice sheet moved south overspreading New England and Eastern Canada. During its peak development, this ice sheet flowed east to southeast across Maine into the sea. The ice itself was thousands of feet thick, with its massive weight shaped the land as it slowly traveled. Climatic warming forced the Laurentide ice sheet to stop and begin to recede as early as 21,000 years ago. This melting of the ice sheet released more water then is possible to imagine.

As the retreating glacier halted for a time the margin would stabilize, thickened as it did north of this location. Here the rushing water carried with it whatever the glacier had picked up along its travels dumping it into the ocean. This area was once depressed by some 400-500 feet as a result of the Earth's adjustment to the tremendous mass of the Laurentide ice sheet that had covered the area. In the area of this earthcache the very fine materials called glacial flour or clay finally settled out as the water slowed.

This is called the Presumpscot Formation and is found all along the Maine coast being named after exposures in the banks along the Presumpscot River Valley near Portland. The formation is blue clay that was formed as the glacial abrasion of bedrock surfaces and rock fragments incorporated into the base of the ice formed a finely pulverized “rock flour” or glacial clay. The marine clay typically has a natural blue-gray color, but near the ground surface, it has weathered to a greyish color. Occasionally you will find large rocks in the formation because icebergs broke loose from the glacial margin and floated out to sea finally melting and dropping their trapped rocks into the clay.

According to University of Maine researchers the unweathered marine clay preserves a wide variety of fossil organic remains, most commonly smaller mollusks (clams) and gastropods (snails). Seaweed, tree remains, large whale bones and seal bones have also been found. All of these species of marine organisms fossilized in Maine glacial clay can be found alive today in the Arctic, demonstrating that our late-glacial sea resembled those found today in Arctic regions.

In the 19th century the “blue clay” supported the now largely defunct brick and tile industry of Maine with almost every coastal Maine village having a kiln for making bricks out of this glacial clay. It was also used by Native Americans to make clay pottery, as well as by early Maine settlers for ceramic products. Today’s, the weathered "blue clay" which is gray in color is used by local potters and artisans for decorative pieces. The down side of this formation can be seen at this location on a much small scale. The glacial clay has the ability to hold moisture and with its location near the surface the expansion and contraction in freeze/thaw cycles often resulting in coastal erosion, which can be made even worse through small landslides triggered by steep shoreline bluffs which often happens here.

Remember this is an earthcache so there is no container just an earth science lesson in an amazing natural area. To log this cache, at the posted coordinates you will find a number of fossils in the blue clay, take a photo of the fossil shell you discover and try to identify what type of common shell that it might be. Most of these shells are very small, less then two centimeters in length. It also would be nice if you would post a photo so others would know what they have to look forward to at this earth cache.

Please make sure that you stay along the shore and do not walk on the top of the bluff. The bluff is small but the glacial clay makes the edge of very unstable. This location is best visited during low tide. Make sure to wear old shoes as the clay sticks to everything, it is not a bad idea to walk back in the water to clean your shoes. After each high tide you will find new fossils in the clay and along the shore. Do not type to remove the fossils from the clay as they are very fragile and break easily. If you look carefully you will find them all along the waters edge near the clay. In high tide when you have waves you can see the clay washed into the water and taken away by the current.

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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