AUSTRALIA: When workers constructing a rail line south of Sydney discovered a trove of Aboriginal artifacts, archaeologists at first were baffled. Many of the stone tools were crafted from flint, which is not native to the area. A subsequent investigation concluded that the flint was actually chemically identical to samples found along the Thames River in London. The flint cobbles were likely loaded onto ships in England for ballast and then discarded in Australia, where they were repurposed by Aboriginal artisans.