where does slate come from in the uk
Slate industry The most significant is that of Cornwall and Devon where the Delabole Quarry is thought to be the largest single quarry in the island. Many of these are no longer worked owing to lower costs of extraction in the larger British workings. The quarrying of slate in Cornwall is known to have been carried out from the late mediaeval period and there was a considerable export trade from some of the quarries near the coasts in the 19th century.
Stonehenge Archaeological excavation has indicated that around 2600 BC, the builders abandoned timber in favour of stone and dug two concentric arrays of holes (the Q and R Holes) in the centre of the site. These stone sockets are only partly known (hence on present evidence are sometimes described as forming 'crescents'); however, they could be the remains of a double ring. Again, there is little firm dating evidence for this phase. The holes held up to 80 standing stones (shown blue on the plan), only 43 of which can be traced today. It is generally accepted that the bluestones (some of which are made of dolerite, an igneous rock), were transported by the builders from the Preseli Hills, 150 miles (240Â km) away in modern-day Pembrokeshire in Wales. Another theory is that they were brought much nearer to the site as glacial erratics by the Irish Sea Glacier[23] although there is no evidence of glacial deposition within southern central England.[24]