Retired Texas A&M professor Jerry Vincent spoke about Maine geology in Bethel Wednesday.
By Terry Karkos
Staff Writer

BETHEL – A retired Texas A&M geology professor condensed roughly 600 million years of western Maine geology into 90 minutes Wednesday night.

“Let’s say we put a person with an infinite life- and food-span atop Mount Washington and give him a power sander with an infinite power supply and an unlimited supply of diamond sandpaper,” Jerry Vincent said.

“Then we tell him his job is to grind down Mount Washington. It’s absolutely ridiculous, but eventually, it could happen. The geologic process takes place over a long period of time. In geologic context, a million years is nothing,” he added.

The free program was the first of this winter’s Mahoosuc Land Trust Local Knowledge Series.

Vincent, who also taught geology at Falmouth and North Yarmouth high schools prior to his college career, simplified the state’s geologic history for a crowd of 52 people at Gould Academy.

After explaining the three types of rock – igneous, sedimentary and metamorphic – Vincent said western Maine doesn’t have any sedimentary strata.

But there are limestones from the Silurian Age (417-443 million years ago) at Ripogenus Dam in Piscataquis County that contain plenty of fossils.

“What we have here are metamorphic plutonium rocks,” Vincent said.

In the early Paleozoic, Maine was a mere accumulation of sedimentary rock on the edge of the pre-North American continent.

Using a squeaky black marker and presentation slate, Vincent illustrated the theory of plate tectonics, drawing that continent converging with another, which he called Avalon, or the Euro/African continent.

According to the theory, each continent sits atop large, semi-rigid plates that float in slow motion atop the Earth’s molten interior.

Vincent termed the resulting collision of the two converging continental plates, “The Big Crunch!”

What was once sedimentary rock was stacked, rolled, squished, compressed and heated tens of thousands of feet below Earth’s surface on the continental margin about 400 million years ago. This process changed the strata to layers of interlocking crystals of different minerals, or crystalline metamorphic rock.

“The Big Crunch formed mountains comparable to the Himalayas,” Vincent said.

And because molten rock was still being squeezed, plutons – large quantities of granitic material – rose up through the metamorphic layers, solidifying underground as the magma crystallized.

One such mass, the Songo Pluton, can be seen from atop Paradise Hill in Bethel, Vincent said. It extends almost to Norway. Most of the gemstone-rich pegmatites in Oxford County formed at this time.

“Plutons make up all of the bedrock in western Maine,” Vincent said.

Maine’s much-prized minerals like tourmaline and beryl accumulated in “garbage cans” of chemicals that got segregated as temperatures cooled, he added.

“Pegmatites can stay as a pocket as things cool down, or they can squirt into sills or dikes or pods. One peculiarity of pegmatites is that their crystal size is enormous,” Vincent said.

As examples, he mentioned the 30-foot-long chunk of beryl that came out of the Bumpus Quarry in Albany Township and yard-long logs of gem tourmaline found in Newry’s Plumbago Mine in the early 1970s.

“Maine is famous for its incredible varieties of minerals. Newry alone has 55 different mineral species that are unique to Oxford County. The only other place in the states that comes close is San Diego County in California,” he added.

Vincent also explained what occurred during Maine’s four major periods of glaciation and what the glaciers left behind as they melted. He also dipped into groundwater, likening the talk to covering World War II in five minutes.

But when pressed to tell the crowd where to find gold in Maine, Vincent clammed up, although he did say that people have been trying to locate the mother lode of gold found in the Swift River for more than 100 years.

tkarkos@sunjournal.com

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