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THE GEOLOGY OF LANGCLIFFE PARISH

Geographical Position

The village of Langcliffe lies to the north of Settle. The parish extends from the left bank of the River Ribble eastwards up the steep limestone hillside to Henside Road, and follows this road southeastwards in the direction of Malham Tarn, to a point just south of Capon Hall. Thus the parish includes Winskill Stones, Blua Scar, Victoria and Jubilee Caves and Langcliffe Scar, but not Black Hill.

Langcliffe Parish lies for the most part between the Middle Craven and the North Craven faults. This means that the rocks are mainly Great Scar Limestone but also include some of the Yoredale Series, both facies belonging to the Lower Carboniferous period. (Facies is a term used to indicate the character of rock strata as expressed by their composition and fossil content, from which their depositional environment can be inferred). Just to the south of Capon Hall the parish boundary crosses the North Craven fault, and consequently Langcliffe includes a narrow band of the Silurian inlier which is exposed to the north of the fault. This inlier extends westwards to the Ribble valley and Crummackdale, and eastwards to just south of Malham Tarn.

Outline of Geological History

The visible geological history of Langcliffe Parish begins in the Silurian period, around 420 million years ago. During these distant times the land surface features of the world did not resemble those of today, neither in shape, size, nor position in relation to the equator. The sediments deposited were derived by erosion from two different directions. At the close of the Silurian period two continental plates collided and the rocks were deformed in open folds. This period of major mountain building is known as the Caledonian orogenesis which lasted from 500 - 380 million years ago.

There are no known rocks in Langcliffe of the Devonian period, which lasted from 410 - 350 million years ago. Perhaps this was a period of erosion or denudation rather than a period of deposition, as the folded Silurian rocks were probably above sea level and being subjected to river based wearing down. In consequence horizontal strata from the Lower Carboniferous period, which followed the Devonian, are found lying directly on top of the eroded, steeply inclined Silurian rocks which preceded the Devonian. This break in the stratigraphic or geological record is known as an unconformity, with the Lower Carboniferous strata being described as lying unconformably on the Silurian. The unconformity seen in the northern part of Langcliffe Parish is part of one of the most well known unconformities in Britain and indeed in Europe.

The Middle Craven and North Craven faults are believed to be extremely ancient lines of weakness, and much older than the Lower Carboniferous period.

The Lower Carboniferous period which began around 350 million years ago is characterised in this area by sediments laid down in a relatively calm marine environment. Scientists believe that the Askrigg Block to the north may not have been deeply submerged, rather like a continental shelf, and the area between the Craven faults was probably a transitional zone between that and the full depth of the Craven Basin to the south. As a result the thickness of Lower Carboniferous rocks in Langcliffe is not as great as further south, and with one exception neither are there deposits from the later Upper Carboniferous Millstone Grit and Coal Measures strata which feature so strongly in West and South Yorkshire. The exception is a small area of Upper Bowland Shales which outcrops against the North Craven fault. These are covered by glacial drift.

After the Carboniferous era the area was subjected, in a period of mountain building known as the Hercynian or Variscan orogenesis, around 270 million years ago, to further earth movements and was raised above sea level. The greatest movements occurred along the lines of the Middle Craven and North Craven faults but there was also faulting throughout the transitional zone. The absence of later rock strata suggest that it has mostly remained as land since that time. Only recent drift deposits dating from the last glacial period are found on top of the Carboniferous beds.

The Silurian Rocks

The Silurian rocks in the inlier on the north side of the Craven fault comprise sandstones and siltstones. They are steeply bedded and part of the Austwick Formation, which can also be seen in Crummackdale. They are sedimentary rocks that were once loose material that was transported by rivers from areas that were being eroded and deposited as the rivers flowed into a sea or ocean basin. The coarser sediments and particles were dumped first and the finer particles were carried farther and settled in deeper water.

The structure of the sandstones indicates that the accumulating sediments were violently disturbed by turbidity currents set in motion by movements in the earth's crust. These currents caused the sediments to cascade down the slopes on which they were accumulating.

At the end of the Silurian period and at the beginning of the Devonian, around 410 - 400 million years ago, the alternating layers of sandstone and siltstone were subjected to great pressure from earth movements associated with the Caledonian folding. The beds were crumpled into tight folds known as anticlines and synclines (upfolds and downfolds), and this folded landscape has subsequently been eroded and partly worn down. What remains of the folded strata is consequently steeply bedded. Most of the Silurian inlier in this area is covered with glacial drift but some of these rocks are exposed in the glacial overflow channel that separates Black Hill from Capon Hall.

The Lower Carboniferous Rocks

Exposed between the Middle Craven and the North Craven faults is the Great Scar Limestone, which is a particularly pure limestone facies of the Lower Carboniferous period. Limestones are rocks composed mainly of calcium carbonate, and the remains of corals, crinoids, foraminifera, algae, and a great number and variety of shell fish. Crinoids are often described as sea lilies because of their appearance but they are animals. They had a long segmented stem and a head part with waving tentacles. Sections of the segmented stem can often be seen in the Great Scar Limestone. The calcium carbonate is derived from the living matter itself and is described as being of biogenic origin. The rocks are mainly light grey and weather even paler. 
The Great Scar Limestone is generally similar in its nature throughout its depth, with obvious bedding planes at all levels and a well developed system of joints. Joints are vertical lines of weakness at right angles to the bedding planes. Both bedding planes and joints are easily widened by the processes of weathering and solution. There are however differences in composition: for example some layers are composed of visible broken shell, plant and animal remains in a fine calcite matrix with up to 50% of the material being organic debris, while other layers are composed of very fine grained materials. Further layers are composed of coarser grained material; and some also show evidence of current action. These variations show a rhythmic pattern resulting from rising and falling sea levels.

One of the first geological surveys of the area, by Garwood and Goodyear in 1924, recognised three index strata in the Great Scar Limestone series: the porcellanous limestone, which is not present in Langcliffe Parish, and two index fossil layers, the Davidsonina (cyrtina) septosa and the Girvanella. An index fossil is a fossil species whose abundance characterises a specific horizon in the strata. A Girvanella layer occurs above Victoria Cave, swings northwards and can be located near Cowside Farm. It is very dark grey in colour and is composed of the fragments of very lowly forms of life including algae. The Davidsonina (cyrtina) septosa was a brachiopod, an unsegmented marine invertebrate with a bivalved shell. Later research and survey work done within the parish boundary by Doughty in 1974 has shown that these bands are well developed and can be traced in six different horizons. Langcliffe Parish can almost be said to have its own index fossil! Complete specimens are rarely found, but fragments of the large ribbed and fluted shell can be seen.

In Langcliffe Parish the rocks of the Great Scar Limestone have been estimated to be not less than 500m in depth. At Blua Crags the strata known as the Malham Limestones are 100m thick. The immense deposits of these limestones that originated and accumulated in calm tropical seas have resulted in massive features with high cliffs and scars, for example Blua Crags and the cliffs that contain Victoria Cave, and in limestone pavements with their characteristic clints and grykes as for example at Winskill Stones. The well jointed, nearly horizontal beds of limestone have weathered into a series of blocks or clints, separated by deep fissures which are known as grykes. Caves with interconnecting passages and shafts are also a common feature of these rocks, and there is extensive literature describing the formation, history and morphology of the systems.

The geological succession then passes from the pure limestone into the deltaic sediments of the Yoredale Series, which are present, but mostly drift covered, in the east of the parish. The succession shows a typical rhythmic type of sedimentation with a gradual change from a marine to a terrestrial environment. Later earth movements interrupted the succession from the Yoredale Series to the rocks of the later or Upper Carboniferous facies. As a result of faulting, sandstones, mudstones and shales of the Upper Bowland Shales occur as an overlap feature and rest unconformably on limestones that belong to the middle phase of the Yoredale Series.

Pleistocene and Recent Deposits

During the Pleistocene age, which lasted from 1ú64 million years ago to 10,000 years BP (Before Present), it is likely that ice sheets covered the area on several occasions. Long interglacial periods when the climate was warmer than it is today also occurred. There is evidence in the clay deposits of Victoria cave of a whole range of animals that must have roamed the area between 135,000 and 114,000 BP, during the Ipswichian interglacial period.

The last glaciation was so intense that it destroyed almost all the evidence of earlier periods of glaciation. As they gradually decayed and melted the ice sheets left thick layers of glacial drift covering the landscape and the remains can be seen in the northern part of the parish in and beyond the upper reaches of Cowside Beck. These deposits can be dated to 13,000 - 10,000 years BP. Erratic blocks of Silurian rock can also be seen perched on top of Great Scar Limestone at Winskill Stones, and indicate how ice could pluck rocks from outcrops in Ribblesdale and carry them to a location that is higher in elevation. These are similar to the well known Norber perched blocks near Austwick.

The current conservation issue with a geological aspect concerns the glacial drift. Being of recent origin, and so at an early stage of consolidation, it produces a soft land surface which is easily disturbed. This is clearly seen east of Jubilee Cave where the track from Clay Pits Plantation to Malham crosses the upper headwaters of Cowside Beck. The soft surface has been badly damaged and widely scarred by the increased use of four wheel drive vehicles. Whether this track is legally used by such vehicles has not been proved. The Yorkshire Dales National Park Authority is campaigning for greater traffic regulation powers which would allow it to control usage at a sustainable level.



Bibliography

Arthurton, R.S., Johnson, E.W., and Mundy, D.J.C. (1988). Geology of the country around Settle. Mem. Br. Geol. Surv., Sheet 60 (England & Wales).

Bell, R. (1996). Yorkshire Rock, a journey through time. British Geological Survey, Nottingham.

Doughty, P.S. (1974). Davidsonina (Cyrtina) Septosa (Phillips) and the structure of the Visean Great Scar Limestone north of Settle. Proceedings of the Yorkshire Geological Society, 40, 41-48.

Garwood, E.J. and Goodyear, E. (1924). The Lower Carboniferous succession in the Settle district and along the line of the Craven faults. Quarterly Journal of the Geological Society, London, 80, 184-273.

Shaw, J.G. (1982). The Geology of the area around Malham Tarn. Field Studies, F.S.C. publication G16. Malham Tarn Field Centre.

Waltham, A.C., Ed., (1974). Limestones and caves of North-west England. David & Charles.

I should like to thank Dr. H. Tombs, Assistant Keeper of Geology at Clitheroe Museum, for her help and for finding five specimens of Davidsonina (cyrtina) septosa in the Museum's collection.


Jo Light

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