Reef knoll
Encyclopedia
A reef knoll is an immense pile of calcareous
material on land that accumulated on the ancient sea floor. At the time of its accumulation it must have had enough structure from organism
s such as sponge
s to have been free-standing and to withstand the sea currents as material accumulated, and was likely an atoll
. Another possibility is the remains of deep water coral
. Such structures are thus often fossil
-rich.
/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
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 may be seen between the villages of Worston and Downham near Clitheroe
Calcareous
Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...
material on land that accumulated on the ancient sea floor. At the time of its accumulation it must have had enough structure from organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s such as sponge
Sea sponge
Sponges are animals of the phylum Porifera . Their bodies consist of jelly-like mesohyl sandwiched between two thin layers of cells. While all animals have unspecialized cells that can transform into specialized cells, sponges are unique in having some specialized cells, but can also have...
s to have been free-standing and to withstand the sea currents as material accumulated, and was likely an atoll
Atoll
An atoll is a coral island that encircles a lagoon partially or completely.- Usage :The word atoll comes from the Dhivehi word atholhu OED...
. Another possibility is the remains of deep water coral
Deep water coral
The habitat of deep water corals, also known as cold water corals, extends to deeper, darker parts of the oceans than tropical corals, ranging from near the surface to the abyss, beyond where water temperatures may be as cold as 4°C...
. Such structures are thus often fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
-rich.
England
Examples on the DerbyshireDerbyshire
Derbyshire is a county in the East Midlands of England. A substantial portion of the Peak District National Park lies within Derbyshire. The northern part of Derbyshire overlaps with the Pennines, a famous chain of hills and mountains. The county contains within its boundary of approx...
/Staffordshire
Staffordshire
Staffordshire is a landlocked county in the West Midlands region of England. For Eurostat purposes, the county is a NUTS 3 region and is one of four counties or unitary districts that comprise the "Shropshire and Staffordshire" NUTS 2 region. Part of the National Forest lies within its borders...
border include Thorpe Cloud
Thorpe Cloud
Thorpe Cloud is an isolated limestone hill lying between the villages of Thorpe and Ilam at the southern end of Dovedale. It is a popular hill amongst the many day-trippers who visit the area, and provides a fine viewpoint north up the dale and south across the Midland plain.Like much of the dale,...
and Bunster Hill in southern Dovedale
Dovedale
Dovedale is a popular dale in the Peak District, England. It is owned by the National Trust, and annually attracts a million visitors. The valley is cut by the River Dove and runs for just over between Milldale in the north and a wooded ravine near Thorpe Cloud and Bunster Hill in the south...
, and also Chrome Hill
Chrome Hill
Chrome Hill is a limestone reef knollon the Derbyshire side of the upper Dove valley. It is adjacent to the more distinctive but lower Parkhouse Hill.Chrome Hill was declared open access land...
and Parkhouse Hill
Parkhouse Hill
Parkhouse Hill is a small but distinctive hill in the Peak District National Park in the English county of Derbyshire. It lies on the north side of the River Dove, close to the border with Staffordshire....
at the northern end.
These structures are often most clearly seen where the surrounding rocks are much softer and so can be preferentially eroded
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
. All the Derbyshire examples quoted lie at the edge of the limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
areas; and Chrome and Parkhouse lie at the divide between limestone and the much softer shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
.
Examples in the Yorkshire Dales
Yorkshire Dales
The Yorkshire Dales is the name given to an upland area in Northern England.The area lies within the historic county boundaries of Yorkshire, though it spans the ceremonial counties of North Yorkshire, West Yorkshire and Cumbria...
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 may be seen between the villages of Worston and Downham near Clitheroe