Duane and Ruth Braun will discuss the geological makeup of MDI on Tuesday, Aug. 28, at 5:30 p.m. at the Southwest Harbor Public Library. PHOTO COURTESY OF RUTH AND DUANE BRAUN

Local history: going way, way back in geologic time



SOUTHWEST HARBOR — Geologists Duane and Ruth Braun will discuss the geological makeup of Mount Desert Island on Tuesday, Aug. 28, 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.” Book sale proceeds will benefit the library and the Maine Granite Industry Museum.

“Their talk will begin around a billion years ago when MDI was attached to the super continent, Gondwana,” event organizers said. “It split from 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. The oldest of these formations is the beautifully 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 the striking landscape here today.

Ruth Braun earned her Master of Science from Johns Hopkins University. She has taught science, math, and geology courses in a variety of high schools and universities.

Duane Braun earned his Ph.D. from Johns Hopkins University. He was the Geosciences Professor at Bloomsbury University. He also mapped the glacial deposits of a 9,000-square-mile area of northeastern Pennsylvania for the Pennsylvania Geology Survey and revised the geologic maps of MDI for the Maine Geologic Survey.

Pre-registration is required for this popular talk. Contact the library at 244-7065.