Reef knoll

A reef knoll is an immense pile of calcareous material on land that accumulated on the ancient sea floor. [Cope, F. Wolverson (1976) "Geology Explained in the Peak District", David & Charles] 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 areas; and Chrome and Parkhouse lie at the divide between limestone and the much softer shale.

Examples in the Yorkshire Dales [cite book |last=Ramsbottom |first=W.H.C. |coauthors= R.F.Goosens, E.G. Smith, M.A. Calver |editor=D.H. Rayner and J.E. Hemingway |title=The Geology and Mineral Resources of Yorkshire |origdate=1974 |publisher=Yorkshire Geological Society |pages=61-64] lie on the downthrow side (north) of the Mid Craven Fault. There is one set located around Thorpe (Skelterton, Butter Haw, Stebden, Elbolton, Thorpe Kail, Myra Bank and Hartlington Kail); one set located around Malham (Burns Hill, Cawden, and Wedber); and a set around Settle (High Hill and Scaleber).

Examples in Lancashire [cite web|url=http://www.english-nature.org.uk/special/geological/sites/area_ID20.asp|title=English Nature: Lancashire Geology|accessdate=2008-09-17] may be seen between the villages of Worston and Downham near Clitheroe

References

External links

* [http://www.bgs.ac.uk/foundation-web/PrkHseHill.html British Geological Survey website, on Chrome, Parkhouse and Derbyshire atolls]