Geology
Water draining from Black Down has exposed rocks from the Devonian sandstones of the Portishead Formation which show through the limestone and mudstone of the Avon Group and younger marine Carboniferous Black Rock Limestone. The northern and lower end of the combe, which was once the bed of the Congresbury Yeo, cuts through Clifton Down Limestone. Triassic Dolomitic Conglomerate can also be seen.
Read more about this topic: Burrington Combe