Flint is a glassy stone, which was commonly used in the prehistoric periods to make tools, such as microliths. In the Post-Medieval period gun-flints were made. It can be easily shaped by knocking it against other stone, bone or wood. The earliest flint tools were made in the Palaeolithic, but most flint tools were made in the Mesolithic and Neolithic. It is being debated if flint use continued into the Bronze Age and Iron Age. Flint can be found in small amounts of pebbles found in the clays along the coastal strip of Northumberland and Durham. It is likely that there are offshore deposits as well - though the dumping of ballast will have confused the picture.