The Winnats Pass is a deep gorge in the Carboniferous limestone near Castleton in the Peak District of Derbyshire. For many years it was thought to be a collapse cave system, current thinking suggests that it was originally a narrow underwater passage between the coral reef knolls formed in Carboniferous times.
BGS: The Carboniferous limestone reef knoll stands above the Hope Valley, informed professional opinion has suggested that when the warm shallow seas allowed the formation of the limestone reef knolls the valley floor roughly represented the deeper water of the then ocean. BGS: Bee Low Limestones Formation (apron-reef) - Limestone. Sedimentary Bedrock formed approximately 326 to 335 million years ago in the Carboniferous Period. Local environment previously dominated by shallow carbonate seas. Setting: shallow carbonate seas. These rocks were formed in warm shallow seas with carbonate deposited on platform, shelf and slope areas; often rich in corals and shelly faunas. May include evaporites where seawater was trapped and salts concentrated by evaporation.