MONMOUTH, WALES—A pair of 100-foot-long channels in the clay could have been used to drag boats into a prehistoric lake, according to archaeologist Stephen Clarke of the Monmouth Archaeological Society. The channels are shaped like the bottom of a canoe, and are accompanied by a third smaller groove that could have been made by a boat’s support arm. No actual boat timbers have been found, but Clarke thinks the area could have supported a settlement and a boat-building industry during the Bronze Age. “I have seen 14-ton machinery sliding in the clay so it would have been easy to push a boat,” he said.