The unusual rock formations of Mount Desert Island are the subject of a talk by geologists Duane and Ruth Braun Sept. 10 at the Southwest Harbor Public Library. PHOTO COURTESY OF WILL DIXON

Geologic evolution of MDI

SOUTHWEST HARBOR — Geologists Duane and Ruth Braun will discuss the geological makeup of Mount Desert Island on Tuesday, Sept. 10, at 5:30 p.m. at the Southwest Harbor Public Library.

They will also sign copies of their book, “Guidebook to the Geology of Mount Desert Island and Acadia National Park.” Proceeds will benefit the library and the Granite Museum.

The talk will begin around a billion years ago when MDI was attached to the super continent Gondwana and eventually attached itself to North America. MDI itself experienced three major geologic events which resulted in the formation of ten different rock units that now make up the island,” said event organizers.

The oldest of these formations is the crenulated Ellsworth schist. Most of the rock on MDI formed around 420 million years ago as alternating intrusions of pink granite and gray gabbro magma fed a huge volcanic caldera the size of MDI. Two miles of rock have been eroded since then to form the present landscape. Over the last 2.5 million years glaciers have repeatedly covered the Island with up to 5,000 feet of ice. When the glaciers retreated they left behind a number of different deposits and landforms, helping to create a beautiful and striking landscape.

Ruth Braun earned a master’s degree from Johns Hopkins University. Over the years she has taught science, math and geology courses in a variety of high schools and universities.

Duane Braun earned a doctorate from Johns Hopkins University and, before he retired, was professor of geosciences at Bloomsburg University. He also mapped the glacial deposits of a 9,000-square-mile area of northeastern Pennsylvania for the Pennsylvania Geology Survey. He has also revised the geologic maps of MDI for the Maine Geologic Survey.

The Brauns have been instructors for Acadia Senior College. Pre-registration is required. Contact 244-7065.

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