Limestone Landscapes in the English Peak District
Limestone is formed from the remains of billions of tiny shells and skeletons.  Most of these decayed totally 300 million years ago, but a few decayed only partially.  Those which decayed least are visible to the naked eye as fossils, others  can only be recognised with a microscope.  Limestone is essentially calcium carbonate plus a few Limestone fossilimpurities.  It is a material that can exist in a variety of forms - the lime scale in kettles for example.   Limestone forms in warm, clear seas and lacks the evidence of tides and currents displayed by gritstone.  Peak District limestone formed over a period of 50 million years, however, and changes in conditions on the sea floor over that time are reflected today in variation in rock colour, strength and fossils.   Occasionally layers of clay or shale were laid down, and these are significant  in the landscape when they act as barriers to ground water and cause spring lines or fracture surfaces for landslips.  "Limestone"  is shorthand for a complex collection of rocks formed over tens of millions of years at various depths.   The purest limestones formed in shallow water and are seen in much of the central plateau,  (east of Buxton for example) and geologists divide them into half a dozen variants.  On the edges of the limestone area are rocks formed in deeper ("basin") conditions.  These have few fossils and a relatively high clay content and can be seen in the Ecton area, embedded in severely folded strata.

The original environment of Lower Carboniferous times can be most easily envisaged looking north from the bottom end of Winnats Pass.  Most of the Peak south of Castleton was a shallow sea in limestone time, but there was a deep area to the north which filled with the muds that eventually,  after uplift and much erosion,  became the kind of shales that make up Mam Tor.
REEF FORMATION -  cross-section through the limestone sea around Castleton  / Winnats Pass
The most significant variations in limestone itself are due to:
REEFS - places where corals flourished, generally on the edge of deep water.  Today they often reappear as hills (e.g. Chrome Hill)  because  their chemistry and stratification are more resistant to erosion than normal limestone.  Winnats Pass was probably formed as some sort of tidal channel in the reef fringing the shallow seas which laid down the limestone plateau; (see diagram).
DOLOMITE- magnesium dissolved in sea water bonded with the hardening limestone and produced an extra hard rock in some localities.

The erosional feature we are usually most aware of are the steep valleys - dales.  The formation of Peak District valleys is a complex subject, but cave collapse in almost certainly a significant process in many of them (Cave Dale, near Castleton had an arch over it's entrance well into historic times, for example).

After the basic limestone had been laid down, sea water circulating underground  precipitated previously dissolved lead, copper, fluorspar and other minerals in spaces due to faulting and settlement.  Man's search for these materials  had a very significant impact on the historic landscape. (The most significant change taking place today is quarrying for limestone to processed  into cement or pounded into building materials.) see:  Peak District Lead Mining

Peak District Geology

For a  hands on experience dealing with the rocks of the Peak, visit the National Stone Centre, Wirksworth :  http://www.nationalstonecentre.org.uk/

Buy "Classic Landforms of the White Peak" from the Geographical Association or Amazon:

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Copyright @ 2003 Stephen N.Wood. All rights reserved.