REEF KNOLL

A 'reef knoll' is an immense pile of calcareous material on land that accumulated on the ancient sea floor.^[1] At the time of its accumulation it must have had enough structure from organisms such as sponges to have been free-standing and to withstand the sea currents as material accumulated, and was likely an atoll. Such structures are thus often fossil-rich.
Examples on the Derbyshire/Staffordshire border include Thorpe Cloud and Bunster Hill in southern Dovedale, and also Chrome Hill and Parkhouse Hill at the northern end.
These structures are often most clearly seen where the surrounding rocks are much softer and so can be preferentially eroded. All the Derbyshire examples quoted lie at the edge of the limestone area; and Chrome and Parkhouse lie at the divide between limestone and the much softer shale.

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External link

Reference

1. Cope, F. Wolverson (1976) ''Geology Explained in the Peak District'', David & Charles

External link

★ British Geological Survey website, on Chrome, Parkhouse and Derbyshire atolls