The study, published in the current issue of the journal Antiquity, indicates that two quarries in the Preseli Hills of Pembrokeshire, in southwest Wales, are the source of Stonehenge’s bluestones. Carbon dating revealed such stones were dug out at least 500 years before Stonehenge was built — suggesting they were first used in a local monument that was later dismantled and dragged off to England. The very large standing stones at Stonehenge are sarsen, a local sandstone. The smaller ones, known as bluestones, consist of volcanic and igneous rocks, the most common of which are called dolerite and rhyolite. Geologists...