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However, such rocks are not always available, meaning that quern-stones have been manufactured from a wide variety of rocks, including sandstone, quartzite and limestone. Quernmore Crag near Lancaster in England is named after the quarrying of millstone grit used to make quern stones in these parts.
The term "Millstone Grit" was also adopted in South Wales where rocks of similar age and lithology are found though the Millstone Grit Series of this region has recently been formally renamed by the British Geological Survey as the Marros Group. The thickest bed of sandstone within it was known as the Basal Grit and this has now been renamed as ...
The natural condition for the quernstone and millstone production in the area is the rock type garnet mica schist. The quarries are located from the shoreline up until approx. 200 m above sea level, but a majority is situated less than one kilometer from the sea and closest harbor.
A very good millstone is generally rich in silica: the higher the percentage, the stronger the rock, silica being the hardest common mineral on the Earth's surface. The same is true of sandstone with siliceous cement, where the percentage of silica is high because both the grains and the cement are siliceous in nature.
The Millstone Grit Group is a formal stratigraphic term for this sequence of rocks. The gritstone edges of the Peak District are an important climbing area and the rock is much relished by English climbers , among whom it has almost cult status and is often referred to as "God's own rock". [ 3 ]
The larger part of the national park is formed in sedimentary rocks from the Carboniferous period (359 - 299 Ma). In stratigraphic sequence i.e. youngest at the top, the sequence consists of: [3] Pennine Coal Measures Group; Millstone Grit Group; Yoredale Group (Asbian - Yeadonian) Stainmore Formation; Alston Formation (inc Gayle Limestone ...
The group records the deposition of fluvio-deltaic sediments which consists mainly of clastic rocks (claystones, shales, siltstones, sandstones, conglomerates) interstratified with the beds of coal. In most places, the coal measures are underlain by coarser clastic sequences known as Millstone Grit , of Namurian age.
Derwent Edge is a Millstone Grit escarpment that lies above the Upper Derwent Valley in the Peak District National Park in the English county of Derbyshire. An Ordnance Survey column marks the highest point of the Edge at Back Tor (538 metres, 1765 feet). [1] North of Back Tor the edge extends into Howden Edge and enters the county of South ...