The geology of the Avon Gorge

Amazing stratigraphy in the Avon Gorge © National Trust

Amazing stratigraphy in the Avon Gorge

For a long time it was unclear what caused the Avon to cut through the limestone ridge, rather than run south west through Ashton Vale towards Weston-Super-Mare. Leigh Woods is situated on the western side of the resulting Avon Gorge.

The Avon Gorge was formed during the last ice age when the original river channel to the south was blocked forcing it to cut its way down through an anticline of carboniferous limestone and old red sandstone. 

Rocks with a difference

A complete succession of the local Carboniferous limestone is exposed in the gorge. This sequence starts with Goblin Combe Oolite in the north, through Clifton Down Limestone, Hotwells Limestone to Upper Cromhall Sandstone at Stokeleigh Camp. The sequence is then truncated by the Avon Fault that runs along the north side of Nightingale Valley, part of it is repeated at the southern end of the reserve.  This variety of rocks creates some interesting habitat types.

The Avon Gorge is an important geological site

It is where Vaughan and Reynolds used marine fossils to date the different strata. This classic section of Carboniferous limestone, the 'Avonian' was adopted as the standard. It is one of Britain's historic geological sites, important for both the study and development of stratigraphy.