Geological Wonders



La Beche Unconformity

The famous De la Beche unconformity in Vallis Vale, which is reached by crossing the bridge at Jackdaws and taking the riverside path for about ½ mile on the left. Here, the angular unconformity is revealed in an old quarry – in simplistic terms, an unconformity occurs when ancient bedrock is forced over at an angle, then eroded until level; subsequent rises in sea level and depositions of sea creatures resulting in the upper limestone strata.

Tedbury Unconformity

Further evidence of this unconformity is to be seen at the old quarry at Tedbury higher up the valley. Go over the bridge at Jackdaws, turn right, proceed over the metal bridge and bear left along the Fordbury Brook until you reach the bottom of a flight of 37 steps. At the top you arrive at the quarry. It’s amazing because now you are standing on a flat Jurassic sea bed (the unconformity).

Jurassic Limestone

On the far side of the quarry you see the much younger yellowish Jurassic limestones deposited perhaps 150 million years later!
Further information can be found on the British Geology Survey

Vallis Vale Caves

Visible Spleenwort Shelter

Whilst there are a number of cave-like holes along the sides of the Mells River, the one most obvious one is Spleenwort Shelter midway between Jackdaws bridge and Peter’s Bridge.

Amazing Elm Cave

The most interesting one and recently rediscovered by Mendip cavers is Elm Cave which is situated between quarry railway line and Tedbury Camp. Mendip Cave Registration indicates exact location – see link. It has to be said that this cave is not easy to find and access to it involves a considerable amount of scrambling.

Mysterious Sinkholes

Another geological curiosity is the Mells Sink; to be found just upstream of the Fussell’s Iron works, mid way between Great Elm and Mells. Essentially, this is a hole in the river bed which acts as a sink or spring depending on the relative heights of river and water table. When water table is high, after heavy rain, the water flows out into the river, but when water table is low water flows in. Tests have proved that emergence is at Hapsford. The Bristol Speleological Society investigated this phenomena between 1974 and 1978 and issued a report. Click here for link to this report of the Mells River Sink.

The Wonders of Geology

Embark on a thrilling geological adventure in the Great Elm’s River valley