Lydney Cliff (grid reference SO654020) is a 8.0-hectare (20-acre) geological Site of Special Scientific Interest in Gloucestershire, notified in 1990.

[1][2] The site has exposures in the Raglan Marls (topmost) of the Lower Devonian time period (up to the level of the Psammosteus Limestone).

The outcrop is significant for research in assessing the extent of marine tidal influence on the sequence in the Lower Old Red Sandstone (below the Psammosteus Limestone).

[1] The site has two important fish beds and the assemblage is regarded as proof of a marine incursion within environments which are predominantly estuarine to fluvial.

This article about a Site of Special Scientific Interest in England is a stub.