The origins od ancient wood discovered buried in Portland remained a mystery until recently.
PORTLAND, Maine (NEWS CENTER) -- When geologist Woodrow 'Woody' Thompson found sections of trees buried in clay in a gravel pit on Portland's western waterfront, he had no idea what he'd discovered.
"Well, this mystery started in 1976, when I was doing some geologic mapping around Portland," explained Thompson. "I was looking in a gravel pit, down near the Fore River next to what was then the Maine Central Rail Road, and I was surprised to find pieces of wood in a clay formation that dates back to the close of the Ice Age."
"It turned out they were well over 10,000 years old," he added. "So that is how the mystery got started."
The trees encased in clay did not look that old, in fact some of the white spruce limbs still had needles on them that were green. How they got there puzzled Thompson and other scientists who came to work on the mystery.
"These pieces of wood don't fit your notion of a fossil. They don't look like the petrified wood that is millions and millions of years old," said Thompson. "This is very fresh looking wood. It looks as though you could put a match to it and it might still burn."
After exploring the issue as far as he could at the time, Thompson moved on to doing other field work for the Maine Geological Survey, but the tree mystery was something he would discuss with other geologists on occasion.
In 2007, thirty-one years after he made the initial discovery, work began on Mercy Hospital's Fore River campus. While construction crews were digging the foundation, Thompson returned to the site, where construction crews had found a virtual forest of splintered logs and limbs buried throughout the property.
Thompson sent samples of the wood to be radiocarbon dated to get a more accurate estimate of their age. When word returned that the preserved trees were approximately 13,500 years old, Thompson and his colleagues were able to get a better picture of what had occured thousands of years ago.
The trees had been growing on Bramhall Hill, which at the time was an island, surrounded by the receding waters of the Atlantic. As the glaciers retreated from the Maine coast at the end of the last Ice Age, the water level also dropped.
Sometime all those years ago, the marine clay that composed the western slope of the hill (today's Western Promenade) became destabilized, and a massive landslide - hundreds of feet wide - occured. The trees became buried in the marine clay and lay perfectly preserved for thousands of years.
"This find in Portland is, so far, the largest and best preserved accumulation of ancient wood that anybody has found in Maine, and perhaps in all of New England,"stated Thompson.
Scientists have been able to use information gathered studying the trees to get a better understanding of Maine's forest history and the climate changes that occured at the end of the last Ice Age.
The information has also proved useful for more modern applications - understanding the types of ground compositions that are susceptible to landslides.
Thompson is glad to have the mystery solved, and he and his colleagues have written and published an article about their research a major scientific journal, 'Quaternary Research', and have also presented their findings to the Geological Society of America.
"It feels really great, because it has been nagging at me for 31 years," said Thompson, of finally figuring out the story behind his find. "Every gravel pit is a window into the past."