Geology and landscape Development

The Geology and Landscape of the Rylstone Area

The landscape of Rylstone and its surrounding area, as we see it today, has been formed as the combined result of:

the sequence and character of the underlying rocks
earth movements which have reconfigured the rock formations through faulting, folding and tilting at various times during the geological past
the combined forces of ice, water and temperature change which have eroded the surface and near-surface rocks over millions of years and, latterly, re-sculptured the landscape during and after the last ice age
the influence of humans by their land use, habitation and economic activity over the centuries.

Dales geology

Rylstone lies near the northern edge of what is known geologically as the 'Craven Lowlands' or 'Craven Basin'. The main rock types which we see at the surface - forming both the rocky bottoms of local streams, such as Hetton Beck, and the sides and tops of Rylstone Fell - belong to the Carboniferous period which lasted from some 360 to 300 million years ago. All the more recent formations have been removed by erosion since that date. A simple geological timeline is given in Figure 1 below to show the sequence of events relevant to the Dales.

Fig.1: Geological timeline for the Dales, after Waltham, T. (2007).

Underlying the Carboniferous rocks are the older and folded sedimentary rocks of the Silurian and Ordovician periods which lasted from about 490 to 410 million years ago. These ancient slates, sandstones and gritstones have been intruded by the once-molten Wensleydale granite (now known from isotope data to be about 400 million years old and to date from the early Devonian period). Both have then been heavily eroded. Together, they form the Askrigg Block which rises to the north of Rylstone and underlies much of the more northerly Dales area. It has provided a long-stable platform for later sedimentation and a bulwark against the forces of later earth movements (see Figure 2; Wilson, A. (1992)).

In Lower Carboniferous times (which lasted from about 360 to 325 million years ago), England was part of a greater continental block known as Avalonia and lay near the equator. Shallow, warm seas overlaid the eroded Askrigg block, such as we find in the Caribbean today. As a result, sedimentation was mainly of limestones, including the various beds of the iconic Great Scar Limestone (such as the Kilnsey, Cove and Goredale Limestones). These massif and often fossiliferous limestones, which are interspersed with thin shales and sandstones, form major escarpments and cliffs in valleys such Malhamdale and Wharfedale. Above the main limestones are the Yoredales - a cyclical sequence of thinner limestones, shales and sandstones which represent fluctuating coastline conditions where deltaic and shoreline sediments were followed by periodic incursions of shallow marine beds. The Yoredales often form the higher reaches of the dale sides and give them a particular stepped appearance.

Fig. 2: Foundation rocks of the Dales from Wilson, A. (1992) for the Dales

National Park Authority.

As we progess south from Wharfedale towards Rylstone in Lower Carboniferous times, the shallow seas and deltas of the upper Dales gave way to deeper water conditions. However, before we reach Rylstone, there is a border area, known as the 'Cracoe Reef Belt', where apron reefs or mounds of calcareous muds and debris, occasionally with patches of fossils, were formed at the edge of the deeper water. Despite some erosion and the effects of earth movements, these knolls are still key features of the landscape and have been the subject of considerable geological attention (see for instance, Bond, G. (1949)). The largest of the reefs (Swindon) is the site of longstanding quarrying activity because of the purity of its limestone content.

Rylstone rocks

When we reach Rylstone at this geologic time, there was not only much deeper water, but also muddier and more turbid sedimentary conditions. Here, thick sequences of dark grey muddy limestones, shales and mudstones were laid down in a marine environment similar to that found currently in the North Sea (see Booker and Hudson, 1926).

The rock sequence which outcrops at the surface in and around Rylstone begins with the Thornton Limestones, which include the locally named Hetton and Hetton Beck limestones. Hetton Beck Limestone is visible in the stream bed above Hetton bridge on the north western boundary of Rylstone parish. Above these limestones, and forming the central and lower lying area of Rylstone village and parish, are the Worston Shales, which outcrop in various stream beds, banks and small cuttings and have a number of limestone bands contained within them.

These are followed by Pendleside Limestone, a horizon which is known locally as Rylstone Limestone and is seen at Clints Quarry, close to the railway line to the south west of Rylstone. Above this are the thick Bowland Shales which form the concave and poorly drained slopes of Rylstone Fell, with the occasional gulley cutting through them (see Figure 3). Contained within these softer shales is the occasional harder band of darkish limestone.

Forming the rocky promontories and peat-covered summits of Rylstone, Cracoe, Boss Moor and Barden Fells, as well as the tops of many other dales hills, are the extensive Millstone Grits. These thick and coarse sandstones were laid down in warm deltaic conditions in Upper Carboniferous times after the earlier sea had retreated. This period lasted from 325 to 300 million years ago. Rylstone Cross sits on one of the most prominent of the grit edges and Norton Tower is well sited on a lower, outlying hill also made from this massive form of sandstone.

Above Rylstone there are still scars on the fell sides from where the grits were quarried for local use in house-building, wall construction and for millstones. Within the Grits are some narrow coal beds, such as found on Boss Moor, with the coal being dug out for local consumption here up until the first decades of the 20th century.

Fig. 3: Geology and landscape of Rylstone Fell area.

A geological sketch map of the Rylstone area is given in Figure 4 below. This is a compilation of information given in British Geological Survey (1948 and 2002), Waltham, T. (2007) and Wilson, A. (1992).

KEY

Northern Block

Millstone Grit

Yoredales

Great Scar Limestone

Ordovician-Silurian

Southern Basin

Millstone Grit

Worston/Bowland Shales

Thornton Limestone

Reef knolls

Fault

Anticline fold

Syncline fold

Fig. 4: Sketch map of the geology of Rylstone and surrounding areas.

Reconfiguring the Rylstone formations

As can be seen from Figure 4, Rylstone sits within a zone which has been subject to considerable faulting and folding. The parish is located in a faulted and subsided basin between the South and Mid Craven faults, with the Mid Craven Fault being instrumental in forming, for example, Malham Cove. According to Wilson (1992):

'Whereas the Middle Craven Fault moved mainly during Carboniferous times and marked the Southern limit of the Askrigg Block, the other giant faults - the North Craven, South Craven and Dent Faults - continued to be active into post-Triassic times.'

Indeed, these faults are still active to this day as the very occasional small earthquakes felt in the area testify.

The faulting has been accompanied by consequential uplift and tilting (e.g. of the Askrigg block both before and during Carboniferous times), and subsidence (e.g. of the Craven Basin during the Lower Carboniferous period, partly occasioned by the heavy sedimentation of this period).

The area has then been subject to folding with most of the folds trending south west to north east, as Figure 4 depicts. These are considered to be from the Variscan earth moving period which occurred at the end of the Carboniferous period. They form part of what has been termed the Ribblesdale Fold Belt. One such local fold is the Hetton anticline, located to the West of Rylstone and the Skipton anticline to the south-east.

Within the immediate area of Rylstone Parish, the faulting and folding is rarely seen at the surface and appears to have had a limited effect on the current landscape. Such features as Waterford Gill, however, may well have resulted from erosion along underlying fault lines.

Sculpturing the local landscape

Rylstone Parish is situated in an unnamed valley located between the larger Wharfedale and Airedale valleys. It is bounded and dominated by the gritstone crags of Rylstone Fell on the east, and by the lower and more rounded Boss Moor on the north west.

Like all the Dales, the Rylstone area has been subject to glaciation, with the last Devensian ice age finally retreating from the area about 11,500 years ago after a long period of gradual warming. Mention has been made (see Figure 5 below) of there having been a temporary glacial lake which stretched from the Linton and Swindon area down to Cracoe, Rylstone, Hetton and onwards towards Skipton.

Fig. 5. Sketch of supposed late-glacial lake in the Linton-Rylstone area (drawn by Mary Stoney in consultation, it is believed, with Arthur Raistrick).

This may have been created by blockages caused by the Wharfe glacier and Aire ice-sheet and by later accumulations of morainic debris further down the valley as the ice retreated. A number of such lakes have been recognised in the Dales (see Raistrick and Illingworth, 1967, p.34).

Today, the central part of the Rylstone area is one of hummocky terrain, largely due to the thick, but variable, mantle of glacial till or moraine which largely masks the underlying bedrock below. One notable feature, thought to be a moraine, is the elliptical mound in Coonlands Hill field, by Rylstone railway crossing and to the left of the Hetton to Cracoe road (see Figure 6 below).

Fig. 6: Moraine in Coonlands Hill field.

This distinct mound still bears the marks of medieval strip lynchets, cut into the moraine's slopes to allow arable crops to be grown during the warmer medieval period.

Chapter 28 of the Geodiversity Plan for the Dales aptly catches the character of the southern valleys enclosed by Winterburn Moor, Rylstone Fell and Flasby Fell, as the following statement suggests:

'(The) Valleys lack strong character and have (a) gentle longitudinal gradient with no distinct dale head...' and 'act as transportation corridors for roads and the mineral railway'. Moreover, 'unscreened limestone quarries at Swindon and Embsay detract significantly; other detractors (are) absorbed in distinct viewpoints by tree cover)'.

Rylstone lies at the watershed between the Wharfe and the Aire catchment areas. Although there is no major water course within the township, there appears to have been ample water to meet the needs of the developing parish which is fed and drained by a number of small becks. The most prominent of these is 'Hetton Beck', as it is generally known today, which forms much of the lower western boundary of the parish, and flows into the Aire at Gargrave. Interestingly, this stream progressively changes its name on the OS map from 'Sunhill Beck' in Fleets, to 'Skirse Gill Beck' below Fleets, to 'Hetton Beck' below Hetton Bridge, to 'Flasby Beck' in its lower reaches where it joins with Eshton Beck at Eshton Bridge. The water flows of Hetton Beck, to the south-west of Rylstone, were harnessed by a corn mill in early medieval times, which then became a woollen mill in later centuries.

A much smaller and shorter beck, which rises on Rylstone Fell, flows past the old Rylstone Manor close to its fish ponds, which it may have fed, and down through the village to Rylstone Pond, created by filling in the old parish green. It then joins Hetton Beck near Burton House.

A range of other east-west flowing rills, and the occasional deeper gulley, drain an extensive area of boggy upland (occasioned by boulder clay lying above impermeable Bowland Shales) on Rylstone Fell as Figure 3 shows. Of particular note is Waterford Gill which is a deep ravine that cuts down through both the Millstone Grit and Bowland Shales of Rylstone Fell to the east of Scale House.

Thus the lands of Rylstone Parish have been formed by the enduring and oft repeated processes of rock formation, earth movements, glaciation and erosion. At the same time, today's landscape has been shaped by the detailed impacts of mankind and this topic is dealt with in the website section entitled, 'Landscape and Land Use'.

Bibliography and References

Booker, K. M. and Hudson, R.G.S. (1926). 'The Carboniferous Sequence of the Craven Lowlands South of the Reef Limestones of Cracoe'. Proceedings of the Yorkshire Geological Society. Vol.20. pp.411-438.

Bond, G. (1949). 'The Lower Carboniferous Reef Limestones of Cracoe, Yorkshire'. Quarterly Journal of the Geological Society. No. 418.

British Geological Survey. (1985). Geology of the Northern Pennine Orefield. Volume 2: Stainmore to Craven. London: HMSO.

British Geological Survey. (1993?). Settle: England and Wales Sheet 60. Solid Edition 1:50,000. Nottingham: BGS. Copyright: Swindon: NERC.

British Geological Survey. (2000). Holiday Geology Map: Yorkshire Dales. Nottingham: BGS. Copyright: Swindon: NERC.

British Geological Survey. (Fourth Edition: 2002). The Pennines and Adjacent Areas. British Regional Geology. Nottingham: BGS. Copyright: Swindon: NERC.

Ensom, P. (2009). Yorkshire Geology. Stanbridge, Wimborne: The Dovecote Press Ltd.

Harrison, D.J. (1982). 'The Limestone Resources of the Craven Lowlands. Description of parts of the 1:50,000 geological sheets 59, 60, 61, 67, 68 and 69'. Mineral Assessment Report 116. Institute of Geological Sciences for NERC. London: HMSO.

Hudson, R.G.S. and Mitchell, G.H. (1937). The Carboniferous Geology of the Skipton Anticline. Summary of Progress of the Geological survey of Great Britain and the Museum of Practical Geology for the Year 1935: Part II. London: HMSO.

Kidd, A., Cooper, A. and Brayson, J. (2006). Your Dales Rocks: Draft Geodiversity Action Plan 2006-2011. Available from North Yorkshire Geodiversity Partnership at: http://www.nygp.org.uk/documents.php.

Raistrick, A. (3rd edition, 1974). Ice Age in Yorkshire. Clapham: The Dalesman Publishing Company.

Raistrick, A. (1976). Prehistoric Yorkshire. Clapham: The Dalesman Publishing Company.

Raistrick, A. and Illingworth, J. L. (1967). The Face of North-West Yorkshire. Clapham: The Dalesman Publishing Company.

Rodgers, P. R. (1978). Geology of the Yorkshire Dales. Clapham: The Dalesman Publishing Company.

Sunderland, B. (re-issued 2nd edition, 1982) The Shaping of the Dales. A Guide to the Geology of the Yorkshire Dales. Ingleton: J.W. Tennant and Son.

Waltham, T. (2007). The Yorkshire Dales: Landscape and Geology. Ramsbury, Marlborough: The Crowood Press.

Wilson, A. (1992). Geology: An In-depth Look at the Yorkshire Dales Park Landscape. Grassington: Yorkshire Dales National Park Committee.

Yorkshire Geological Society. Editor: Scruton, C. (1994). Yorkshire Rocks and Landscape: A Field Guide. Maryport: Ellenbank Press.