Time to read the definitive guide to the geology of the Peak District and other Pennine regions.
Pre-carboniferous rocks. There are some outcrops of Ordovician and Silurian rocks in the Yorkshire Dales (near Ingleton, Horton-in-Ribblesdale and Malham) but non in the Peak District area. These have been shown to underlie the Peak District in borehole studies.
Dinantian deposits outcrop to the north of this region on the Askrigg block and Craven basin, and to the south as the Derbyshire dome. The Derbyshire dome consists of the Derbyshire and Staffordshire platforms separated by the Widmerpool Gulf. The Derbyshire platform deposits are from the ramp and shelf of the platform but not the slope and basin which outcrop to the south in the Widmerpool Gulf region.
Platform - thickly bedded, pale grey to grey, massive bioclastic limestones (packstones and grainstones), dolomitised limestone and dolomite. Woo Dale Limestones, Bee Dale Limestones and Monsal Dale Limestones.
Ramp - grey to dark grey, thinly bedded bioclastic limestones (packstones) commonly with chert nodules and pale grey micritic limestones forming knoll reefs (mud mounds).
The rocks of Namurian age form the continuous outcrop which forms the Pennines. It divides at the south of Edale to outcrop on either side of the Derbyshire Dome. Course grained to granular, feldspathic sandstones are the dominant characteristic of the Millstone Grit Group. Ashover Grit near Derby and Chatsworth Grit near Leek form the oldest rocks and overlie the Namurian mudstones of the Edale Shale Group (these also contain sandstones but their proto-quartzitic composition distinguishes them from the Millstone Grit Group).
The successions are of a remarkably cyclical nature marked by regular marine transgressions which define the base of each cycle. There are 46 + 3 more recent of these recognised. They were caused by the growth and decay of the Southern Hemisphere ices sheets.
The rocks are mostly formed from mud, silt and sand carried into the Pennine basin by a large river system from mountains in Scananavia and Greenland. The abundance of fresh feldspar show the erosion and rapid transport from granitic source. The sea level changes also controlled delta growth stopping as sea level rose, and starting again as it fell.
The lower Westphalian Coal Measures were laid down in the Pennine basin between the Southern Uplands High and the Wales-Brabant High. They were laid down as a continuous strata but the movements associated with the Variscan Orogeny in the late Carboniferous and early Permian deformed them into gentle folds. Erosion left only those in the downthrown areas intact. The outcrops are to the east and west of the Namurian sandstones and ad not well represented in the Peak District.
Limestone
The Carboniferous limestones of Derbyshire were famous as decorative stones, commonly termed 'marbles' by the trade because of their ability to take a high polish, their varied colours and attractive structure.They included the Ashford Black Marble, Birds Eye Marble. Rosewood Marble, Duke s Red and Muscle Marble. None of these stones are produced today, but they can be seen as decorative inlays in many of the great houses of Derbyshire such as Chatsworth, Hardwick and Bolsover Castle.Today, polished limestones are produced from the Bee Low Limestones at Hopton Wood and Griffeton Wood quarries. Hopton Wood Stone has been used in many major buildings, including the Bank of England and the city halls of Manchester and Sheffield. On a sombre note, the creamy grey, crinoidal Hopton Wood Stone provided the headstones for the graves of tens of thousands of British and Commonwealth troops who fell in the 1st and 2nd World Wars.
Sandstone
The exploitation of the Namurian sandstones in the Peak District also has a long history and all the major sandstones have been quarried for building stone. In the High Peak area sandstones of the Shale Grit (at Kinder Bank), Kinderscout Grit (at Chinley Moor, Ladybower and Hayfield), the Heyden Rock (at Thornseat), Roaches Grit (at Combs, Ridge Hall and Longhill), Chatsworth Grit (at Birch Vale and Buxworth) and the Rough Rock (at Cracken Edge) have all been extensively worked. The most important area of sandstone quarrying in Derbyshire lies farther south and east along the Derwent and Amber valleys and the intervening hillsides, where the Namurian sandstones crop along the valley sides from Hathersage to Belper. Quarries have long worked the Kinderscout Grit at Stokehall quarries),the Asbover Grit (at Darley Dale, Birchover, Duke's, Whatstandwell and Stanton quarries), and the Chatsworth Grit (at Yarncliff, Beeley Moor, Bole Hill, Lumshill and Millstone Edge quarries). The Rough Rock from the Coxbench quarries was used extensively for buildings in Derby.The Stancliff Darley Dale Stone is particularly famous for its durability and quality and has been widely used in towns and cities (for example Derby Cathedral, the Guildhall in Nottingham). The Ashover Grit used in buildings in the village of Kirk Ireton is stained pink by percolation of groundwaters through the former Triassic red-bed cover. The Shale Grit was used for the Kinder Reservoir and ’Stokehall Stone’ from Grindleford for the Howden and Derwent Reservoirs and Sheffield Town Hall.
Lead
Lead sulphide mineralisation (galena. PbS) has been worked in the area from large numbers of veins.There are several hundred named veins and many small, unnamed ones.They are up to several kilometres long, less than 10 m wide, of limited vertical extent and steeply dipping and consist of galena, fluorite, calcite and baryte.The major veins are commonly known as 'rakes', the minor ones as 'scrins'. Fluorspar and baryte have also been worked in more recent years and are now the main economic minerals recovered; no veins are now worked solely for lead. Semi-concordant 'flats' have also been worked as at Masson Hill near Bonsall. A few short, tubular, subhorizontal pipe oreshoots also occur, as at Hubberdale pipe.The mineralisation is largely confined to the eastern half of the exposed Dinantian limestone outcrop and is mainly hosted within the Monsal Dale Limestones, where overlying Namurian shales formed an impermeable caprock to the mineralising solution. The most important deposit was at the Millclose Mine near Darley Dale, where over 400 000 tonnes of lead concentrate and 90 000 tonnes of zinc concentrates were recovered from a remarkable orebody where natural concentration of galena in a cave system produced very high grades of mineralisation. Elsewhere in the orefield, the grades were about 5 per cent Pb, the exact figure dependent on the width of vein worked. Modern exploration has continued to develop the orefield, with the emphasis on fluorspar. In the early 1950s, there was an attempt to further develop the Riber Mine on the Great Rake for lead and zinc. Initial boreholes showed promising widths and is of lead mineralisation. However, subsequent underground development showed that miners had removed much of the mineral and that the boreholes had fortuitously through unworked pillars, giving a false impression of the possible resources left in the vein. The mine was closed in 1958. Calcite production continues from the Long Rake vein in the centre of the orefield.
This is very much just the highlights of the book. I expect I will be returning to this book again and again as the journey continues.
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