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Dufton Geology - The Landscape around Dufton

Within a short distance of the village green in Dufton it is possible to see the impact of many of the major geological events which have created the scenery of the British Isles. The effect of continental drift, of volcanic activity, of erosion by rivers, glaciers and weather, of the deposition of material under seas and rivers, and of faults are all visible. What we see as the landscape today is the result of the interplay of these events over millions of years. While much of the evidence of these remains hidden below the present surface, in places there are exposed rocks and other features which show the elements of the story of the making of this landscape. Dufton was a mining village for lead and also for anhydrite, used in chemical and paint industries and to make gypsum, used for plaster and wall boarding..


Background: Throughout geological history the land which forms Britain has drifted northwards from latitudes now occupied by southern Africa. This provided a succession of tropical and equatorial-type climates which resulted in very different conditions over time. The earliest geological history is one of deposits under the surface of a sea which varied in depth. Fine grained silts, more coarsely grained sandstones, underwater volcanic tubes, all produced the basis of rocks which can be seen in the Dufton area. The later eruption of the volcanoes in modern Borrowdale resulted in the deposition of ash, up to 1000 metres deep.


The land sank, and the shallow warm sea covering it was home to small shellfish and corals which, when they died, formed the carboniferous limestones. During the same period igneous (liquid volcanic) rock was pushed into the spaces between the carboniferous rocks to form the Whin Sill. At the end of the Carboniferous period earth movements led to folding of the rocks. The subsidence of the Eden valley caused the downfall along the edge of the Alston Granite, a large solid block of granite located deep under the Pennines to the north. This movement, known as the Pennine Fault, led to the formation of the very obvious division between the hills to the north and the Eden valley.


Desert conditions prevailed and sand was moved across the area by wind. The edge of the fault between the valley and the hills was infilled first by the desert sands, and later by waterborne sand which formed the St Bee’s sandstone. Later slippage and movement led to the formation of the present Pennine Fault Scarp. Glaciers moving from the west, the present day Lake District, led to the deposition of clays in the Eden valley, with associated drumlins and melt water channels. There were some small glaciers in the Pennine valleys, particularly that of High Cup Nick. Most of the area was free of permanent ice, but rocks were broken by freezing to form boulder fields, which were moved by water in later periods.


What can be seen?


Dufton Pike, and to the north Knock Pike, are remnants from the creation of the Pennine Fault. Formed of the ash (tuff) from the Borrowdale volcanic period the rocks, when seen close to, form multicoloured deposits. On the south side of Dufton Pike they range in colour from pale pink, pale and dark green to yellow, cream and white. Murton Pike, to the south, is composed mainly of a finely grained slate. This was laid down as mud or silt on the edge of a sea. At the time a line of volcanic islands stretched across what is now the Lake District and the northern Pennines. Over millions of years these mudstones were compressed and heated to form slate, which was folded under pressure.


Rundale: Walking north-east from the village following the path to the south of Dufton Pike above the Rundale Beck, starts on the shales (mud) laid under an ancient sea, passes over the broken mudstone and sandstone of the fault and, if continued towards Great Rundale, covers the Limestone. Where the track bends north (GR705264) the ground on the right shows where the underlying mudstones, which are poorly drained, form marshy ground. Further along the path (GR 709270) there are exposures of quartz. Looking carefully along the path and at the edge, particularly after rain, may be rewarded with small pieces of galena (lead ore) which is grey and shiny. On the opposite side of the valley there are a line of springs where the water meets impervious rock. Higher up towards White Rake (GR725275) there is limestone, dark grey with fine grains overlain by a thin shale, showing a temporary change to the environmental conditions when the rocks were being laid down. White Rake is a hush, used by miners to wash off layers of soil and rock to expose lead ore.


High Cup: The Pennine Way to High Cup Nick towards the south east covers a similar sequence of rocks, from the sandstones in the valley, across the mudstones and through the broken sandstones and mudstones of the Pennine Fault, and into the limestone. The changes in slope along the path mark the changes across different bands of mudstone. At the gate where the path enters the open land of the fell (GR 722250) the carboniferous limestone outcrops are evident all round, and just along the path the presence of a lime kiln shows one of its uses. The most dramatic feature, High Cup Nick, is revealed as the Pennine Way continues eastward towards Teesdale. The term sill was used originally by miners and quarrymen in this area and was later adopted by geologists to describe a rock intruded or pushed between two older rocks. The rock originated as magma, molten rock, deep below the surface and made its way through joints between the layers of rock, and solidified. Being much harder than the surrounding limestone it has formed the sides of the valley, with the wide and deep High Cup Nick being created by both glacial, and later, river, action. The Whin Sill continues across the north of England, forming the foundation of Hadrian’s Wall, and making a final appearance at the Farne Islands and Holy Island in Northunmberland.


Dufton Ghyll: On the left side of the path entering the Ghyll from the Appleby road to the south of the village (GR694245) the cliffs of red St Bee’s Sandsone are immediately evident. The whole of the walk is through the river cut sandstone valley, with some mudstone being visible in the stream and valley at certain points. The sandstone was laid down under water, probably a shallow sea, and the cliff was once a quarry from where stone was taken to build the railway viaduct at Long Marton, and probably some of the sandstone houses in the village.


The Geological Sequence

(shown in millions of years before the present)




Geological Period

Years

Events and Deposits

Ordovician


480

Silts (Murton Slates); Borrowdale Volcanics (volcanic ash based rock which forms Dufton Pike)


Silurian


416

Alston Block of Weardale Granite intruded


Carboniferous


350

Shallow water warm sea limestones; folding and faulting; Whin Sill


Permian


275

Arid, desert conditions, shallow sea, filling of valley formed by fault. St Bee’s Sandstone.


Pleistocene


2.6

Glaciation, Pennine Fault Scarp; High Cup Nick


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