The Ellsworth Schist is the oldest rock on Mount Desert Island. A schist is a type of layered metamorphic rock. It often breaks along the layers, but rather irregularly and contains a lot of a mineral that breaks into thin sheets called mica. Metamorphic rocks are a category of rocks that have undergone changes due to heat and/or pressure.
The example of the Ellsworth Schist at this location is one of the easiest locations to see its characteristics. It is typically dark green or gray with thin layers of white. The layers of white are quartz and feldspar and the dark green is type of mica called chlorite. As you can see, often the layers have many small folds in them that resulted from the pressures that the rock was subjected to during its metamorphosis.
The rocks that eventually became the Ellsworth Schist were initially deposited as mud on an ancient sea floor off the coast of an ancient continent called Avalonia over 500 million years ago. These muds were buried miles beneath the surface where high temperatures and pressures recrystallized and folded the rock into a schist. Later the schist was brought back to the surface and eroded.
Movement of the plates on the surface of the earth resulted in Avalonia and North America colliding. Following the collision, pieces of Avolinia became part of the North American Plate where we see them today.
The Ellsworth Schist is also exposed in places along the north west side of Mount Desert Island and Bartlett Island. The picnic area on Thompson Island also has some exposures at the edge of the cobble beach.
Send me an EMAIL, (not a message) via the user profile link above with the following information :
- The text "GCZ5J0 Ellsworth Schist" on the first line
- The number of people in your group and if anyone is logging separately, their login name(s).
- Compare and approximate the thicknesses (width) of the chlorite and quartz layers on the schist.
- Optional: Post a photo of you and your GPS at the coordinates.
- Extra Credit: Post the coordinates of another outcrop of Ellsworth Schist.
Be sure to check the box to include your email address with your answers so that I can send you the OK to log. Any logs posted before I receive your email and qualify your find or logs containing spoilers will be deleted without prior notice.
The following sources were used to generate this cache:
- Gilman, Richard A., Carleton A. Chapman, Thomas V. Lowell, Harold W. Borns, Jr., The geology of Mount Desert Island A Visitor’s Guide to the Geology of Acadia National Park, Maine Geological Survey Department of Conservation, 1988
- National Park Service, Acadia National Park, Geologic Database to accompany digital geologic maps, acadglg.hlp, version 2004-02-02; 16:11 MST