In 1872, workers digging a hole for a fence post near the shoreline of Lake Winnipesaukee in New Hampshire unearthed a mysterious egg-shaped object, six feet (1.8m) underground. When they wiped away the mud, they discovered the quartzite egg was covered with carvings, including an ear of corn, mysterious circles and, most bizarrely, a face. One hundred and fifty years later we still don’t know for sure who made it or why. At the time, the American Naturalist journal described it as "a remarkable Indian relic", suggesting it was made to commemorate a peace treaty between two tribes. Others have suggested that it's a birthstone or some kind of ancient tool.