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Marginal Way - Oarweed Cove

A cache by BooleanRuler Send Message to Owner Message this owner
Hidden : 10/14/2016
2 out of 5
1.5 out of 5

Size: Size:   other (other)

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Geocache Description:

The objective of this cache is to provide an earth science lesson about the geological conditions of the origin of the rocks and structures of the Marginal Way and Oarweed Cove in Ogunquit in Maine.

Access to the Earthcache area
A waypoint is provided for the southern trailhead where parking also is available (there is a parking fee). The stroll from the trailhead at Perkins Cove to the earth cache area is about a 10-15 minutes scenic walk on the Marginal way along the Oarweed Cove. From here it is not far to Devil's Kitchen which is a great location to really see evidence of the continental collision in the Kittery Formation.


There has been a lot of geological development in the Ogunquit area over time and the Kittery Formation is the second-oldest type of rock formation in Maine, second only to the Ellsworth Schist.

In the Silurian period over 400 million years ago Ogunquit and the Marginal Way was deep in the middle of an ancient ocean called Iapetus between North America and a Microcontinent to the east which was a part of old Africa. Erosion caused sand and clay to be transported down the continental slope to finally settle at the bottom of the Iapetus Ocean.

During the Devonian period, North America and the Microcontinent to the East collided. The collision caused great pressure and temperatures and transformed (metamorphosed) the sandstones and shales formed from the sand and the clay at the bottom of the Iapetus Ocean into high mounting ranges where Ogunquit is today.

In the Jurassic period about 200 million years ago, the Atlantic Ocean started to form due to continental rifting and again created tension on the Ogunquit area. The rifting caused fractures to open up which were filled with Basalt magma. Geologists call this Basalt dykes and these dykes can be seen in the area and all along the Marginal Way. Erosion then continued over the next 150 million years or so and placed the Ogunquit area on the shoreline where it is today.

Rock types

There are in short three main rock types;

Igneous rock. Igneous rock is formed through the cooling and solidification of magma or lava.

Sedimentary rock. Sedimentary rocks are formed by sediment that is deposited over time, usually as layers at the bottom of lakes, oceans or the Earth's surface. The sediment is compressed over a long period of time before consolidating into solid layers of rock.

Metamorphic rock. Metamorphic rocks have been changed over time by extreme pressure and heat. Uplift and erosion help bring metamorphic rock to the Earth's surface. Some examples of specific metamorphic rocks are;

-          gneiss which can sometimes be identified by the occurrence of rock glitters making it spark (gneist in German),

-          phyllite which has a tendency to split into sheets (foliated) and is often black or greenish gray in color,

-          marble which is the ‘shining stone’ and most associate it with the color white but other colors can be found as well such as in the Swedish Green Marble,

-          soapstone which has a soapy feel to it and is often used to create sculptures or make countertops and

-          quartzite which is common in the United States and is usually gray but often occur in shades of pink and red due to varying amounts of iron oxide.

To claim this Earthcache

To claim this earthcache you need to provide the answers to the following questions by using the ‘message the owner’ function on the earthcache page;

1 About how many million years ago was the Devonian period?

2 How many years of geologic history can be studied examining rocks in this area?

3 Based on your observations overlooking the rock formations at the cache location and what you have learned so far, which of the three main rock types do you think can be found here?

4 Identify the specific rock types seen in this area that have formed from metamorphosed sandstone and shale?

Optional but not mandatory;

Post a picture/selfie of yourself at the cache location or post a picture of your GPS with the coordinates showing.

After you have submitted your answers, please feel free log the Earthcache as found and write about your experience. Please don't include any of the Earthcache answers though.

When logging and if you want, you can tell me what kind of birds you have seen on your stroll to the cache area. I saw lots of Double-Crested Cormorants on my last visit and it is always fun to know what observations people make.

Have fun and enjoy your visit.

A couple of days after my visit to Ogunquit and the Marginal way, Professor of Geology Emeritus Arthur M. Hussey passed away peacefully. Much of the information provided above and the requirements for solving this Earthcache are based on his knowledge of the area. All credit should go to him.

Additional Hints (No hints available.)

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