This earthcache will teach you about the type of rocks that predominate here, where they come from, and how they came to be here. Since this is an earthcache, there is no physical container to find or log to sign. Please read through the description below and answer the logging questions.
There are 3 types of rocks on Earth and you can find examples of all 3 in the Bar Harbor Area.
1. Sedimentary rocks called Bar Harbor Formation
2. Igneous rocks called Cadillac Mountain Granite
3. Metamorphic rocks called Ellsworth Schist
For this EarthCache, we are going to focus on two of these, the Bar Harbor Formation and Cadillac Mountain Granite.
The Bar Harbor Formation is obviously named for the nearby town. You can see lots of bedrock exposure along the shoreline at the pier and along the public walking trail. So where did this rock come from? This rock was laid down at the bottom of an ancient ocean about 460 million years ago. The sediments at the bottom of that ocean were cemented together to form the rocks that you see today. If you look closely, you can see alternating layers of darker gray and lighter ash colors.
In several places in this area, you will find large granite boulders that don't see to belong here, including Balance Rock here at the edge of the water. When you look at Balance Rock, you can see that it is a different color and texture than the Bar Harbor formation bedrock on which it rests. It is characteristic of Cadillac Mountain Granite, which formed about 420 million years ago as magma oozed up through cracks in existing rocks and then slowly cooled.
Geologists believe this particular piece of Cadillac Mountain Granite came from about 40 miles northwest of here, around the Lucerne/Bangor area. The glacier ice that brought this rock to this location was more than a mile thick and advanced in a northwest-to-southeast direction. Towards the end of the Ice Age, the glacier melted and retreated. The glacier's advance and retreat carved out many of the bays, lakes, mountains, and valleys as they currently appear in this area.
All rocks will eventually weather away, but they don't all do it at the same rate. Typically, sedimentary rocks will erode faster than the igneous rocks. Why? Sedimentary rocks will have weaker layers, called bedding planes, that can easily be broken apart by weathering. Physical weathering of water, wind, and ice will cause the bedding planes to expand and break away, causing cracks in the rocks that erodes away. This freeze/thaw cycles can be seen in the cracks in the local bedrock along the shore. Igneous rocks like this granite did not form in layers, but cooled as one large mass. Granite rocks will therefore not have the same bedding planes, so they are not usually affected by freeze/thaw as much as the sedimentary rocks.
Logging tasks:
1. Explain how the balance rock got to this location.
2. Compare the weathering of the Balance Rock to the bedrock it is sitting on.
3. Take a close look at the texture of the Balance Rock and compare it to the texture of the Bar Habor formation.
4. Which do you think will erode faster, the granite Balance Rock or the sedimentary Bar Harbor formation? Explain why.
5. Post a picture of yourself (face not required) or a personal item at Balance Rock.
Sources: digitalmaine.com, geology.teacherfriendlyguide.org, nps.gov/acad/learn/nature/geology.htm and pesonal knowledge