Stimulation - Knowledge - Interaction - Fun
Dear Members and Friends,

Fall classes are underway - several are meeting in person and others by Zoom. As a reminder, please respect the mask policies of our in-person host sites. For your safety and that of your classmates, please wear masks indoors (even though you are vaccinated), and distance in the classroom where possible.

Our Food for Thought series will begin on September 24th with a presentation from the ASC Racial Justice Committee. We'll continue the series virtually for the time being.

Check out the rest of the news below and don't forget to join us for our 20th Anniversary Party on Wednesday, September 8th from 4 - 6. The gathering will be outdoors with music, food, a slide show, and a special proclamation read by Secretary of State Shenna Bellows.
See you soon,

Janice Kenyon, ASC Administrator
No RSVP required - we hope to see you there!

Friday, September 24th at Noon

Virtual presentation via Zoom

Recently the ASC Board convened a Racial Justice Committee to respond to concerns about racism in our community and our world. Join us on September 24th to learn about the impetus for the committee, the issues the group explored, the Board's response to the committee report, and how ASC plans to engage with issues of systemic racism and racial equity in the future.

This event is free and open to the public.

As part of its work in the spring of 2021, the Racial Justice Committee is forming a Racial Justice Book Group that will begin meeting in the fall of 2021. The group will be meeting by Zoom starting September 15th.

Those interested in joining the group(s) can contact Ellen Dohmen at

In addition, the group has compiled a suggested reading list for people interested in the topic. You can find the reading list and learn more about the book group here.

The deadline to submit course proposals for Winter 2022 is Friday, September 24th.

Have an idea for a class? We're looking for online offerings, in-person classes or perhaps a combination. Flexibility is the name of the game these days!

What life experience, expertise, or adventure are you eager and willing to share? What writer has been your life-long favorite? Which artists inspire you with their masterpieces? What unforgettable foreign travels have you taken? Your ASC friends look forward to escaping the winter doldrums and joining with you to share stimulation and knowledge.

Geology Corner - The Fracturing of MDI’s Bedrock

By Ruth and Duane Braun

Note: this is the 6th in a series of articles on the Geology of Mount Desert Island. Thank you Ruth and Duane! You can read the previous installments in past newsletters on our Newsletters page.

As the 420 million years ago or so collision of the Avalon Terrane with the Gander Terrane ended, Mount Desert Island’s volcano stopped erupting and no more magma was injected at depth. Then the 10 mile wide and 4 to 5 mile thick mass of molten magma gradually cooled to a rigid solid over a 10 million or so year period. Around 360 million years ago the Meguma Terrane (present day Nova Scotia) collided with Avalon-Gander Terrane and this produced more magma intrusions (Seawall granite) and pressure from the collision fractured the now cool rigid rock on MDI. 

This occurred again around 300 million years ago when the continent of Gondwana collided with Maine and the rest of the eastern United States. Compression from these large-scale collisions, or Tectonic events, cause the solid rock to break along near vertical fractures (Photo 1 below). These vertical tectonic fractures propagate or extend slowly over years to even 1000’s of years and this slow development often produces nearly perfectly planar fractures. People often misinterpret such perfect fractures as human cut features.
Photo 1 - Near vertical tectonic fractures cut gently sloping sheeting.
The once deeply buried old igneous rock bodies are actually compressed by the weight of the overlying rock. As erosion removes the overlying rock, the once buried underlying rock expands (strain release or unloading) parallel to the ground surface (technically the surface of lowest confining pressure). These unloading fractures form sheets of rock that are near horizontal under gently sloping landscapes (Photo 1 above), and steeper under more steeply sloping mountain sides.

These two mechanisms have resulted in intersecting horizontal and vertical fractures that naturally break the bedrock into rectangular blocks (Photo 2 below). These fractures also produce surfaces for weathering to act upon, breaking up the rocks further. The closer together the fractures, the smaller the resulting blocks of rock are. The closer spacing also helps to speed up weathering and erosion of the bedrock. So inland valleys and bays along shore form where there are more closely space fractures. The road cuts along the northern end of Somes Sound show some of these more closely spaced fractures. Granite quarrying takes advantage of these natural vertical and horizontal fractures to help guide the breaking out of blocks from the quarry face.
Photo 2 - Rock face broken into rectangular blocks by vertical tectonic fractures and near horizontal unloading fractures.
The high mountain range formed from all the collisions began to be eroded during the collisions and thereafter, particularly as Pangaea broke up 200 million years ago to start forming the Atlantic Ocean. By the start of the ice ages 2.5 million years ago the landscape resembled the ridge and ravine landscape of a more gently sloped version of today’s Smokey Mountains.

MDI’s old magma chamber was a low NE to SW trending mountain range or drainage divide with low saddles between the gently rounded peaks (Diagram 1 below). Streams flowed north on the north side of the low range of mountains. Then they flowed west to drainage along the present Blue Hill River valley or east to the Skilling River valley and into Frenchman’s River valley. Those on the south side drained south toward the opening Atlantic Ocean. Just like in the Smokeys today, there were no lakes on these river systems. The 420 million years of collision and erosion resulted in a gently sloping ridge and ravine landscape on MDI that was then to be sculpted into its present form by at least five glaciations over the last one million years.
Diagram 1 - Landscape of MDI immediately prior to glaciation.
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