HISTORY & KEEPERS

SHELL heaps called middens provide a record of Native Americans and climate.

Alice Kelley stood on the bank of a tidal river, next to a grassy bluff dotted with beautiful apple trees. This is not just a scenic spot : Hidden beneath the grass is a huge pile of oyster-shells left by Native Americans.

And hidden among those shells are rich, detailed stories thousands of years old.

Middens like this one line Maine's tortured shoreline. ''We know that there are over 2,000 shells heaps on the coast Maine,'' said Dr. Kelley, an associate research professor at the University of Maine Climate Change Institute.

''In virtually every case here in southern Maine, they are disappearing or they are gone.''

Dr. Kelley was speaking at Maine's best-known example, the Whaleback Shell Midden State Historic Site, during a recent conference she organized to discuss the vulnerable shell heaps.

While many of  New England's Native  American artifacts have decomposed in acidic soils, those in midden are often well preserved, as the calcium carbonate in the shell creates more alkaline conditions.

The middens hold clues not only to ancient cultural practices, but also to historic environmental and climatic conditions.

Most have never been studied. Some have been raided by looters. And many are eroding as sea-levels rise.

Seas have generally been rising in Maine since  Ice Age glaciers retreated 15,000 years ago.

Rising waters had transformed the  Damariscotta estuary into an optimal oyster habitat by the time this midden, and another across the river, were created.