Avon Gorge - Geology and Formation

Geology and Formation

The gorge cuts through a ridge mainly of limestone, with some sandstone. This particular ridge runs from Clifton to Clevedon, 10 miles (16 km) away on the Bristol Channel coast, although limestone is found throughout the Bristol area. The fossil shells and corals indicate that the limestone formed in shallow tropical seas in the Carboniferous, 350 million years ago. For a long time it was unclear what caused the Avon to cut through the limestone ridge, rather than run south west through the Ashton Vale towards Weston-super-Mare. However, Bristol was at the southern edge of glaciation during the last ice age, and it has been suggested that ice blocked the river's natural route through Ashton Vale to the west. At the Clifton Suspension Bridge the Gorge is more than 700 feet (213 m) wide and 300 feet (91 m) deep.

In the 18th century the gorge was quarried to produce building stone for the city. Stone was taken by boat into the floating harbour. In the 19th century celestine was discovered in Leigh Court estate and the Miles family authorised quarrying. Between 1880 and 1920 Bristol was producing 90% of the world's Celestine, but the enterprise did not last long into the 20th century. Bristol Diamonds, brilliant quartz crystals found in geodes in Dolomitic Conglomerate in the gorge, were popular souvenirs for visitors to the Hotwells spa in the eighteenth and nineteenth centuries. Quarries on the Bristol side of the gorge are now popular with climbers and are a habitat for Peregrine falcons and other wildlife.