I don't know if it's available anymore, but the book I have is The Greater Gungywamp: North Groton, CT, A Guidebook by David P. Barron & Sharon Mason. ISBN # 0892-1741

There's a lot in there about the Standing Stones, stone shelters built by "early man," and runes/writings which correspond to those elsewhere on the east coast and other countries which are unexplainable according to what we know of history.:-)