Stockdale Beck in Longsleddale is known for Silurian graptolite-bearing mudstones. The small exposure described near the old barn and bridge is separate from the more extensive Browgill reference section upstream. This protected beck requires care: arrange access and collecting permission, leave banks and bedrock untouched, and avoid high water or unsafe footing.
FIND FREQUENCY: ♦ – The original visit described a very thin graptolite-bearing bed, but its precise modern correlation and present exposure are uncertain. Fossil bands elsewhere in the beck belong to separate sections.
CHILDREN: ♦ – Deep or fast-flowing water, slippery slabs and steep banks make this unsuitable for children’s collecting.
ACCESS: ♦♦ – Reached through Longsleddale on a narrow valley road. Confirm lawful parking, the walking route and permission before entering the beck or collecting.
TYPE: – Stream exposures in protected mudstone and siltstone. Conditions depend on rainfall and water level; do not enter during high flow.
DIRECTIONS
♦ From Kendal, follow the A6 north and turn into Longsleddale, continuing along the single-track road towards Sadgill. Keep passing places, farm gates and entrances clear.
♦ The original guide approached along the Stockdale track past farm and older centre buildings to a barn and bridge. Arrange access before following that route, and do not use the centre’s private parking as a public car park.
♦ Use only an authorised parking place and allow for a longer walk if necessary. The former roadside and grass spaces are not confirmed current parking arrangements.
♦ The old lower-barn guide marker is 54.44206°N, 2.78508°W. The scientific Browgill reference section around NY 4919 0549 is a separate upstream exposure; neither reference is permission to enter the channel.
♦ Ask the landowner about current access and collecting conditions. Use a mapped, safe walking route and keep out of the beck when the water is deep, fast or rising.
FOSSIL HUNTING
The original UK Fossils visit concentrated on a thin, steeply inclined black bed below the old barn and bridge. It described pale, silver-looking graptolites, sometimes around 10 cm long, and called the horizon the murchisoni Zone. Those are historical observations. The exact bed has not been independently matched to a modern measured section, and colour or length cannot establish either the species or its age.
Graptolites were colonial marine animals. Their preserved branches may show rows of tiny repeated structures, but fossils can be flattened, incomplete or mineralised, and later deformation may change their shape. A silvery sheen is a preservation feature rather than a reliable species character. Photograph the whole fossil with a scale and include its surrounding rock when seeking an identification.
The more extensive scientific section upstream is different. It preserves an upper Skelgill graptolite band and a Browgill succession of pale mudstone interrupted by thin dark fossiliferous layers. Three lower black bands are followed higher up by the well-studied crispus succession, with at least 23 separately identified collecting bands. These are small-scale scientific horizons, not a continuous thick seam to excavate.
The wider Brow Gill–Stockdale locality is associated with the type record of Pseudoretiolites perlatus perlatus. The adjacent Rake section also has documented faunas including Monograptus crispus, Streptograptus exiguus and Retiolites geinitzianus. These records belong to their published sections and horizons; they do not identify the old barn-side specimens or show that every species occurs at the visitor’s original spot.
For a permitted visit, favour observation and photographs from secure ground. The old guide already recorded damage where collectors had cut back the small face. Leave the bank and bedrock alone, and do not treat stones in the stream as automatically available to split or remove. Scientific collecting needs agreed conditions that protect the thin fossil bands and their context.
If a loose specimen may be retained under the landowner’s conditions, note exactly where it was found and that it was displaced. Keep counterpart surfaces together, wrap fragile edges and avoid trimming away surrounding features. Rounded structures in the separate upstream volcanic rocks may be spherulites rather than fossils, while the documented Ordovician trilobite horizon is much older than these Silurian graptolite beds.
Significant discoveries, geological research and conservation milestones at Stockdale Beck.
1836 – The upstream felsite is recognised
Sedgwick distinguished the felsitic rock of the separate upstream Ordovician volcanic section. This is an early geological observation of the rocks now placed in the Yarlside Volcanic Formation, not a discovery in the younger Silurian fossil beds.
1868 – A distinctive graptolite enters the scientific record
Nicholson named the graptolite later cited as Pseudoretiolites perlatus perlatus. The wider Brow Gill–Stockdale locality is its recorded type locality, although the precise bed cannot be assigned to the guide’s barn-side exposure.
1872 – The Stockdale Shales are named
Aveline and Hughes introduced the locality-derived name Stockdale Shales, with the paler upper beds distinguished as Pale Slates. This established terminology that later evolved into the modern group and formation framework.
1888 – The two beck sections are described in detail
Marr and Nicholson described the rocks of Brow Gill and Stockdale Beck and introduced the Browgill Shales name. Their detailed treatment of The Rake concerned a separate Brow Gill exposure, not the lower Stockdale collecting spot.
1965 – The geological section receives protection
The site then known as Browgill Section was first notified as a Site of Special Scientific Interest. Its boundary was revised in 1975 before the later notification under its wider two-beck name.
1974–1975 – The fossil bands are refined
Hutt’s graptolite studies provided the numbered fossil-band framework, including the three lower Stockdale bands and the numerous thin crispus horizons. The work made detailed comparison possible without implying that every part of geological time was preserved.
1979 – An Ordovician trilobite is described from the beck
McNamara described Gravicalymene susi from a holotype on the south-east bank of Stockdale Beck below the Brow Gill junction. Its original horizon was recorded 25 m above the base of the former Applethwaite Formation. This is a separate Ordovician type locality, not the Silurian graptolite bed by the barn.
1979 – Dating the upstream volcanics prompts a wider debate
Gale and colleagues published a 421 ± 3 million-year rubidium–strontium result from the separate upstream volcanic section and used it in time-scale calibration. Later reassessment questioned its meaning because alteration can disturb that dating system. It is not an accepted age for the Ordovician eruption or for the Silurian fossil beds.
1985 – The upstream volcanic body is reinterpreted
Millward and Lawrence mapped a continuous felsite outcrop in the separate upstream Ordovician section, rather than the previously suggested three lavas. They proposed a hot ash-flow deposit that continued to flow after welding, or rheomorphic ignimbrite. The distinction from a true lava remained debated.
30 June 1987 – The two-beck SSSI is renotified
Browgill and Stockdale Becks was renotified with boundary changes, recognising the importance of the combined sedimentary and volcanic geological landscape.
December 1988 – Collecting damage prompts conservation concern
A contemporary conservation account reported damage to fossil exposures and problems with trespass and gates. Advance-permission arrangements were part of the response; the historical contact details do not establish today’s landowner or current consent.
1994 – The modern Stockdale hierarchy is formalised
Revision of the regional succession established the modern group and formation framework and assigned the pale uppermost Browgill beds to the Far House Member.
1997 – Conodont fragments are reported from the red bed
Wang and Aldridge recorded blackened fragments of Dapsilodus and Decoriconus from calcareous nodules in Stockdale’s upper Browgill red horizon, adding microscopic fossil evidence to the section.
1999 – High-resolution work identifies missing time
English’s correlation of Stockdale Beck with Spengill identified substantial gaps in the local turriculatus record, including the maximus interval. The apparently continuous mudrocks therefore do not preserve a complete record of that biozone.
2000 – The classic two-beck geology is synthesised
The geological conservation account brought together the Stockdale reference section, The Rake and their fossil and sedimentological significance, while preserving their separate geographical identities.
2012 – Formal names and section roles are updated
The revised framework specified the modern formations and members and distinguished the Brow Gill type exposure from the Stockdale Beck reference section. Updated graptolite boundary conventions also changed how the lowest Brathay beds are related to the Llandovery–Wenlock boundary.
GEOLOGY
Stockdale Beck crosses more than one geological interval. The main Silurian reference section exposes the Stockdale Group, particularly the Browgill Mudstone Formation, and passes upwards towards the Brathay Mudstone Formation of the Tranearth Group. Llandovery is the earliest Silurian series; it is not the end of the period. The original lower-barn bed was assigned historically to the younger murchisoni interval, which would place it in the early Wenlock if that identification is correct.
The pale and dark mudstones record changing conditions on a marine seafloor. Fine sediment accumulated while graptolite remains settled from the water above. Differences in oxygenation and preservation help explain why conspicuous fossils are concentrated in certain black bands rather than spread evenly through the sequence. High-resolution work favours settling of fine sediment for the correlated beds and warns against explaining every pale layer as a sediment-gravity-flow deposit.
The record is incomplete. A strike fault removes most of the lower Skelgill succession in the Stockdale reference exposure, bringing older Ash Gill rocks close to preserved upper Skelgill beds. Within the Browgill interval, later correlation also identifies missing time. A succession can appear orderly on the ground while failing to preserve a continuous record of geological time; absent intervals should not be filled in using beds from The Rake or another locality.
Above the richly graptolitic crispus interval, pale mudstones give way to a red nodular horizon and then uppermost pale beds. Stockdale records the westernmost development of these upper Browgill red beds in the Lake District. Their small conodont fragments are laboratory fossils from calcareous nodules, rather than conspicuous objects to look for in a hand specimen. The upper transition to flaggy Brathay sediment is geologically useful, but changing conventions for the Llandovery–Wenlock boundary mean it should not be treated as a simple fixed time boundary.
The separate Ordovician volcanic section farther upstream tells a much older story of volcanic rocks and their associated sediments. It includes the Yarlside felsite type succession and lies outside the Silurian graptolite log. The expanded account keeps this background and the neighbouring Rake comparison separate from the Stockdale reference beds and the small original visitor exposure.
Detailed geology of Stockdale Beck, with separate comparisons to Brow Gill and the upstream Ordovician rocks.
Stockdale Beck contains several different geological localities. The original collecting account concerns a small exposure below the old barn and bridge near Stockdale Farm. The classic Browgill reference section lies farther north in Stockdale Beck, while The Rake is a separate exposure in Brow Gill. Still older volcanic rocks crop out upstream. The sections below keep their measurements and fossil records separate; a published rock description is not a route or permission to approach it.
The Stockdale reference section north of the farm. Around NY 4919 0549, the succession is an important reference for the Browgill Mudstone Formation within the Windermere Supergroup. The formal type section is in Brow Gill, rather than at the barn-side collecting point. Llandovery is the earliest Silurian series, and younger Brathay rocks also occur in the area.
DENT GROUP
Ash Gill Mudstone Formation
Ordovician rocks beneath the fault. Ash Gill mudstones occur below the preserved lower part of the Silurian section. No complete thickness is established at this spot. Their proximity to younger rocks does not demonstrate an uninterrupted Ordovician–Silurian boundary here.
STOCKDALE GROUP
Skelgill Mudstone Formation
Strike fault and omitted lower beds. Most of the Skelgill succession is cut out by a fault running approximately along the beds. The fault brings upper Skelgill strata beside the older Ash Gill rocks. Beds missing here cannot be restored by adding measurements from The Rake or Skelghyll Beck to this section.
Black fossil band 7. The preserved upper Skelgill interval contains graptolites of the Aeronian sedgwickii Biozone. It is labelled band 7 on the published Stockdale map. No individual thickness is established for that mapped band.
Browgill Mudstone Formation
Lower pale mudstones. Pale mudrocks dominate the Telychian succession, interrupted by much thinner black graptolitic layers. Individual thicknesses are not available for every pale interval, and the number of dark layers should not be mistaken for a complete record of elapsed time.
The three lower fossil bands: collective measurement. A published comparison based on the classic Stockdale log describes three black layers with a combined thickness of 5 cm within 0.6 m of pale beds. That is a collective black-rock thickness, not 5 cm for each layer. The three mapped bands are distinguished below.
Band 8. This is the lowest of the three mapped lower Browgill graptolite bands, historically placed in the turriculatus interval. Its individual thickness and a complete band-specific species list are not established in the available description.
Band 9. The middle of the three mapped black bands forms part of the same thin fossil-bearing interval. It has a separate identifier, but there is no sound basis for assigning it an invented thickness or a fauna borrowed from an adjacent exposure.
Band 10. The highest of the three mapped lower bands completes this part of the classic log. A maximus Sub-biozone assignment from a neighbouring section should not be attached to it automatically.
Missing time in the turriculatus interval. High-resolution correlation with Spengill concluded that at least 47% of this biozone, including its maximus subdivision, is absent at Stockdale Beck. The estimate concerns an incomplete stratigraphical time record, not a thickness of rock that can be inserted in the exposed section. A correlated interval is 3.8 times thicker at Spengill, illustrating the different sedimentary records at the two sites.
The crispus fossil-band succession. At least 23 thin graptolitic black bands occur within pale mudstone above the lower three bands. The classic comparison gives 4.8 m for the enclosing succession. The individual bands have not each been assigned a recoverable numerical thickness or a complete taxon list, and later fine-scale work may distinguish additional dark laminae between the collecting horizons.
The published sub-band identifiers. The sequence is labelled 11/1, 11/2, 11/3, 11/4, 11/5, 11/6, 11/7, 11/8, 11/9, 11/10, 11/11, 11/12, 11/13, 11/14, 11/15, 11/16, 11/17, 11/18, 11/19, 11/20, 11/21, 11/22 and 11/23. These are 23 subdivisions of band 11, not beds numbered 11 to 23. Their identities preserve the original fossil-record framework without implying equal thickness or equal spacing.
Pale beds above the last fossil band, about 6 m. The last recorded graptolitic layer is followed by approximately 6 m of pale mudstone from which graptolites have not been recorded in the cited section. This is a measured interval within Stockdale Beck, distinct from the shorter upper exposure at The Rake.
Red nodular mudstone. A prominent red horizon above the pale interval contains abundant calcareous nodules. A sample yielded a few blackened conodont fragments assigned to Dapsilodus and Decoriconus. Neither the bed’s numerical thickness nor a directly demonstrated local graptolite zone is established. The microfossils are laboratory records, not a promise of readily visible specimens.
The red bed’s wider significance. Stockdale Beck is the most westerly development of these red mudstones described in the Lake District account. Older interpretations proposed material eroded from a desert landscape and accumulation in hollows on the sea floor. These remain historical explanations of the red-bed distribution, rather than proof of a particular desert or an independently dated local climate event. The named Hebblethwaite Member farther east is not assigned to this exposure.
Far House Siltstone Member
Uppermost pale beds, 4 m. The top of the Browgill succession consists of approximately 4 m of pale, unfossiliferous mudrock, with calcareous nodules or patches concentrated towards its base. The older account called them Grey Beds and described their mudstone lithology. Their modern placement in the Far House Siltstone Member does not erase that original local description.
TRANEARTH GROUP
Brathay Mudstone Formation
The upper contact. The change from Browgill pale beds to the flaggy Brathay succession is fairly sharp. Older schemes placed the Llandovery–Wenlock boundary at the base of the centrifugus interval; the later British scheme uses the base of murchisoni. The formation contact should therefore not be treated automatically as an exactly located series boundary.
The original barn-side exposure. The 2004 visitor account describes a steep to near-vertical black layer only a few centimetres thick, with silver-coloured graptolites, some reported as about 10 cm long. It was attributed to the murchisoni Zone, which would place it in the early Wenlock Brathay succession. That precise correlation and the species identifications have not been independently tied to a modern measured section. The observations concern the lower-barn spot, not the whole beck or the reference section farther north.
Loose stream fragments. A displaced fragment has no guaranteed original bed position. Its sheen, colour or size cannot by itself identify a species or biozone. The original account’s loose collecting material is a historical observation, and does not establish current permission to remove it.
Changing oxygenation and sedimentation. The pale and dark mudstones record changing sea-floor conditions: pale, more oxygenated intervals contrast with black graptolitic sediment deposited under lower oxygen levels. Earlier descriptions proposed distal turbidites for some pale beds. Later geochemical correlation favoured sediment settling through the water column for the compared fine-grained facies, so not every pale layer should be labelled a turbidity-current deposit. That study also found some laminated black beds partly or wholly altered during burial to chlorite nodules, occasionally with manganese-carbonate cores. The altered beds helped correlate magnetic-susceptibility patterns between sections 32 km apart; they are not a newly defined bed or a promised visible find.
The Rake in Brow Gill: a separate comparison. The following beds belong to the classic cleft in Brow Gill, described near NY 4965 0580; the formal framework gives a nearby type-section reference at NY 4974 0587. They help explain the regional sequence but are not measurements of the original Stockdale barn-side exposure.
STOCKDALE GROUP
Skelgill Mudstone Formation
Possible basal Spengill equivalent, 0.05 m. Weathered rottenstone occurs in places below the acuminatus beds in Brow Gill. Its proposed equivalence to the Spengill Member is tentative; it is not a confirmed member exposure at the lower Stockdale collecting point.
Basal pale shale, at least 1 m. At The Rake, pale shale with acuminatus Biozone graptolites overlies Ash Gill rocks. The persculptus interval may be absent at this contact. This differs from the fault-truncated sequence described in Stockdale Beck.
Faulted middle Skelgill beds. Black mudstone horizons at The Rake represent the magnus and convolutus biozones. Paler, occasionally calcareous layers contain trilobites and brachiopods. Faulting disrupts the sequence, and no complete individual thickness inventory is available for these beds.
Upper blue mudstone, 3 m. The uppermost Skelgill interval at The Rake is described as approximately 3 m of blue mudstone without recorded fossils. This measurement belongs to Brow Gill, not the preserved band 7 interval in Stockdale Beck.
Browgill Mudstone Formation
The Rake’s lower graptolite horizon. A historically described Spirograptus turriculatus-rich band lies about 6.5 m above the formation base. The published Rake account also describes three 50 mm black layers assigned to the maximus subdivision. These statements must remain attached to The Rake: they differ from the Stockdale comparison’s combined 5 cm measurement, and later correlation identifies maximus as missing at Stockdale.
The Rake’s crispus horizon. About 6 m above its lower graptolite horizon, fossiliferous black layers become more frequent. Recorded forms include Monograptus crispus, Streptograptus exiguus and Retiolites geinitzianus. This is a local Brow Gill record, not a verified species list for the barn-side bed in Stockdale Beck.
Top of the exposed Rake section, 2 m. Pale calcareous shale without recorded fossils forms the uppermost approximately 2 m described there. It represents the lower part of the upper Browgill succession, not the complete upper formation or Stockdale’s 4 m Far House interval.
A historic graptolite type locality. The wider Brow Gill–Stockdale geological locality is associated with the type record of Pseudoretiolites perlatus perlatus, originally named in 1868. Its exact type-bearing bed has not been recovered here, so the record cannot be assigned specifically to the modern visitor’s barn-side layer.
The separate upstream Ordovician volcanic section. The Stockdale Beck volcanic conservation site extends across roughly NY 477 049–493 060. Its rocks are much older than the Silurian graptolite beds and belong to a different scientific section. The following measurements explain that upstream setting only; they do not continue the lower-barn fossil log.
DENT GROUP
Stile End Formation
Sediments beneath the volcanic rocks. Fine-grained sandstone and conglomerate form an irregular upper surface below the Yarlside volcanic succession. Volcanic material locally fills small depressions in that surface. No measured complete thickness of these sediments is supplied for this beck exposure.
Yarlside Volcanic Formation
Basal lapilli-tuff in the western part of the site, about 10 m. Medium-bedded volcanic rock has a flattened, welded-looking texture, with altered lapilli-sized fragments and felsite clasts. This western basal exposure is distinct from the measured main felsite section in Stockdale Beck.
Main felsite unit, 180 m. Near Stockdale Beck, east of Mere Crag, the type section contains an almost completely exposed 180 m unit of rhyolitic felsite. The lowest 45 m is strongly flow-folded; the uppermost 30 m is massive, with textures recording an originally glassy rock. The intervening part combines these facies. These intervals are subdivisions of the 180 m unit, not additional thicknesses above it. The 60 m succession near Sadgill Wood is a different exposure.
Nodular and spherulitic facies. Expanded spherulites commonly reach about 20 cm across and may enclose cavities later filled by quartz and smaller amounts of other minerals. A different basal nodule type west of the beck near NY 489 056 reaches about 40 cm and lacks a central cavity. These are volcanic and alteration structures, not corals or other fossils.
Upper tuffs and reworked beds. Unbedded tuff occurs in the upper part of the formation in and immediately east of Stockdale Beck. Near NY 498 061, beds at the top reach about 40 cm individually and contain reworked volcanic glass and pumice fragments. Their individual thickness is not a further formation total to add to the 180 m section.
Kirkley Bank Limestone Formation
Carbonate succession above the volcanics. A basal conglomerate contains felsite pebbles eroded from the underlying volcanic rocks. The younger marine beds belong to the Ordovician succession and should not be confused with the Silurian Browgill mudstones simply because both occur along the beck.
The separate trilobite type horizon. The holotype of Gravicalymene susi came from locality 4a on the south-east bank of Stockdale Beck below the Brow Gill junction. Its original description placed it 25 m above the base of the unit then called the Applethwaite Formation. That is an Ordovician fossil horizon, distinct both from the Silurian graptolite beds and from the hillside Stockdale quarries.
References.
Aldridge (2000), Brow Gill Beck, British Silurian Stratigraphy, including figure 3.57.
Millward and Stone (2012), BGS Ordovician and Silurian framework.
English (1999), high-resolution correlation of Stockdale Beck and Spengill.
White and colleagues, comparison with Hutt’s Stockdale fossil-band measurements, manuscript p. 18.
Millward, Stockdale Beck, Longsleddale: the separate volcanic section.
McNamara (1979), Lake District Ordovician trilobites.
Natural England: Browgill and Stockdale Becks SSSI.
SAFETY
Check rainfall and stream conditions before setting out. Water can rise quickly, and deep or fast-flowing sections, wet slabs and steep banks are dangerous. Do not enter in high flow, after heavy rain or when a safe route cannot be maintained; a season name alone is not a reliable guide to safety.
Keep away from unstable faces and do not undercut the bank or prise rock from steep beds. Do not reach across deep water or stand in the channel to photograph or sample a fossil. Turn back if conditions worsen.
Wear boots with a firm grip, carry waterproof clothing and a current map, and let someone know your plans. The beck is not suitable for casual family collecting, and the return route should remain safely accessible throughout the visit.
EQUIPMENT
Bring suitable walking boots, weatherproof clothing, a map, drinking water, a hand lens and a camera with a small scale. Keep your hands free on uneven or slippery ground.
For an expressly permitted collection of loose material, use soft wrapping, labels and a rigid box. Do not bring tools with the assumption that the bedrock, banks or stream stones may be split; agree any sampling method beforehand.
CLEANING AND TREATING
Graptolite films and thin mudstone surfaces can be damaged by vigorous brushing or washing. Begin with light dry cleaning, support fragile slabs and let damp material dry slowly at room temperature.
Keep both sides of a split specimen and preserve exact locality notes. Avoid acids, bleach, routine varnish and aggressive mechanical preparation. A scientifically interesting specimen with secure bed information should be left unprepared for specialist advice.
IDENTIFY YOUR FINDS
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FURTHER READING
Deposits: Cumbria’s ancient volcanoes, regional background
GCR: Brow Gill and Stockdale Beck Silurian sections
BGS (2012): Stockdale and Tranearth stratigraphical framework
English (1999): high-resolution correlation of the Stockdale mudstones
Natural England: Browgill and Stockdale Becks SSSI
GCR: the separate upstream Ordovician volcanic section
ACCESS RIGHTS
Stockdale Beck forms part of the Browgill and Stockdale Becks SSSI. Ask the landowner before entering collecting areas or taking specimens, and check current conditions. The protected designation and a walking route do not provide automatic permission to remove fossils.
Leave the beck banks, bedrock and thin fossil bands undisturbed. Proposed scientific sampling should be discussed with the landowner and Natural England beforehand, with any required consent arranged. Do not assume that permission to walk includes splitting loose stones, modifying a bank or clearing scree.
It is important to follow our ‘Code of Conduct’ when collecting fossils or visiting any site. Please also read our ‘Terms and Conditions‘
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