The wooded slopes of Gallt Yr Ancr, west of Meifod, contain shell-rich Ordovician sandstone associated with old quarries. Brachiopod moulds and occasional trilobite fragments reveal a marine fauna in the rocks beside the Glyndwr’s Way walking route.
FIND FREQUENCY: ♦♦♦ – Historically, suitable shell-rich sandstone yielded numerous brachiopod moulds; many other blocks are unproductive.
CHILDREN – The woodland route has roots, uneven slopes and old quarry edges; supervise children closely.
ACCESS – Use signed public routes. A short woodland approach does not establish access to adjoining quarry ground.
TYPE – Late Ordovician sandstone blocks and old quarry exposures on the northern wooded flank of Gallt Yr Ancr.
DIRECTIONS
♦ Approach the wooded northern flank of Gallt Yr Ancr west of Meifod using the signed Glyndwr’s Way route. The original guide describes a small layby near the woodland entrance; check current signs and stop only where lawful, without blocking access.
♦ The original route reaches a gate after roughly 100 m, with a rising side path beyond it. Follow the waymarked public route rather than treating every side path or nearby slope as open access.
♦ Original approach reference: 52.70895, -3.26565. This is a historical guide reference, not a newly surveyed parking point or the precise location of the scientific quarry specimens.
FOSSIL HUNTING
The most promising sandstone has concentrations of shell moulds along bedding surfaces. On a naturally broken edge these may appear as curved hollows arranged in a narrow band; a weathered bedding plane can reveal a much more recognisable assemblage of ribbed brachiopods. Many blocks lack such shell concentrations, so inspecting visible surfaces is more useful than treating every sandstone fragment as fossiliferous.
Brachiopods dominate the original guide’s finds. Their shells may have dissolved, leaving external moulds of the ornament or internal moulds recording the shell interior. Both are useful, and the two sides of a split preserve different information. A hollow is not necessarily an incomplete specimen: it may retain a detailed impression of a shell that is no longer present.
A historical exposure near Dyffryn yielded material described in 1959 as Paucicrura sowerbii, alongside Dalmanella horderleyensis and Broeggerolithus. These are published historical identifications from a particular quarry exposure, not names to apply automatically to every loose block beside the present path. The older brachiopod nomenclature has subsequently changed, and unlabelled photographs should remain identified at the level the specimen supports.
Occasional trilobite pieces occur amongst the shells. Look for a curved, regularly segmented or ridged surface rather than assuming any angular fragment is a trilobite. Complete animals are not an ordinary expectation here. Similarly, crinoid records from historical collections do not justify promising complete crinoid crowns in path-side debris.
Photograph a fossil-bearing surface with a scale and record its actual location, rock type and whether the block is loose or in place. Do not assume quarry rubble can be freely removed or split because it lies near a public path. Any authorised specimen should retain both matching halves and enough matrix to preserve its context.
Significant discoveries, geological research and conservation milestones at Gallt Yr Ancr.
1959 – Local brachiopods clarify a confused historical species
Cave and Dean used specimens from the exposure near Dyffryn in their study of material historically named Paucicrura sowerbii. The figured dorsal and ventral moulds provide a precise published record for the locality, rather than a date of first discovery.
2008 – District geology places the shell beds in context
The modern district account distinguished the fossiliferous Gaer Fawr sandstones from younger black shale and clarified the regional succession used to interpret the hillside’s older fossil records.
2025 – Montgomery Group framework introduced
A revised stratigraphical synthesis included the Gaer Fawr Formation in the Montgomery Group, providing a modern framework for the shell-bearing sandstone without changing the provenance of the historical specimens.
GEOLOGY
The fossiliferous sandstones belong to the Gaer Fawr Formation. Their historical fauna was assigned to the Lower Longvillian part of the Caradoc regional succession, within the Late Ordovician. The shell beds pre-date the substantially younger Hirnantian episode.
The regional succession records a shallowing marine shelf in which silt and sand became increasingly important. Shell-rich and locally calcareous beds preserve marine organisms that were concentrated and reworked by storms. This explains why fossils can be abundant on a particular bedding surface yet scarce in another block of apparently similar sandstone.
The 2025 framework places the Gaer Fawr Formation in the Montgomery Group. Older accounts describe its relationship to underlying Pwll-y-glo strata and younger regional units, but the short woodland walk does not expose a demonstrated complete vertical succession. The regional formation thickness of 200–360 m cannot be read as the thickness visible on this hillside.
Nod Glas is a younger black mudstone or shale unit, not a younger sandstone formation. Its regional presence does not establish a safely accessible exposure on the guide’s path. The geology chart therefore centres on the documented fossil-bearing sandstone and its shell horizons, without adding neighbouring quarries or a speculative stack of regional formations.
The shell-bearing Gaer Fawr sandstones, historical fossil evidence and locality limits at Gallt Yr Ancr.
MONTGOMERY GROUP
The 2025 framework includes the Welshpool area’s Pwll-y-glo and Gaer Fawr formations in the Montgomery Group, reflecting late Soudleyan–Longvillian progradation. This is the framework used here; the Eryri Group is not transferred across the regional fault boundary into this locality.
Gaer Fawr Formation
The formation comprises increasingly thick sand and silt beds, locally calcareous and rich in shells. It succeeds Pwll-y-glo strata regionally and records a shallowing shelf with storm reworking. The published regional thickness is approximately 200–360 m, not a measured section along the woodland path. No formal member or numbered local-bed succession is securely established for this guide’s accessible exposures.
Shell-rich sandstone horizons. Brachiopod concentrations are preserved as moulds on bedding surfaces and as shell sections or hollows on broken block edges. The original guide records occasional trilobite pieces with the brachiopods. These observations concern local sandstone blocks and old quarry debris; they do not demonstrate that each loose block can be tied to a named bed.
The historical exposure near Dyffryn. Cave and Dean described a large exposure approximately 440 yards just north of west of Dyffryn, about half a mile south-west of Meifod Church. They recorded Paucicrura sowerbii, Dalmanella horderleyensis and Broeggerolithus, assigning the fauna to the Lower Longvillian. Their exact scientific exposure must not be equated automatically with every modern path-side block or used as a replacement visitor entrance.
Figured specimens and historical nomenclature. The 1959 study figured exact-site paratypes BB24885, a dorsal internal mould, and BB24886, a ventral internal mould. Plate 53 figure 8 shows the former; figures 9 and 11 are two views of the latter, not two separate specimens. The historical name Paucicrura sowerbii is retained here as the name used in that publication, without asserting that it is the current accepted combination.
Broader Meifod material kept separate. The historical holotype GSM Geol. Soc. Coll. 6852 was labelled only ‘Myfod’; its association with other fossils does not establish a Gallt Yr Ancr occurrence. The 1839 ventral illustration was composite and the original ventral specimen was not certainly located. Plate 53 figure 10 in the 1959 paper is Shropshire material, while figures 1–6 concern other localities. These specimens are therefore not additions to the hill’s exact fauna.
Regional younger rocks and excluded comparisons. Nod Glas is black mudstone or shale, not sandstone, and its accessible occurrence on the short path has not been confirmed. The regional Guilsfield, Middle House and Pwll-y-glo thicknesses, basal phosphorite, Dolhir/Graig-wen strata and younger Hirnantian episode are not a measured local stack here. The Lower Longvillian shell-bearing sandstone pre-dates the regional Hirnantian episode.
Limits of the bed-level reconstruction. A later account refers to King’s bed C2 in discussing historical crinoid material, but the complete 1928 original section and the published taxonomic revision have not been verified together. The connection between the historical bed reference, crinoid collection and precise hillside exposure remains uncertain. The historical evidence supports fossiliferous sandstone horizons more securely than a detailed numbered vertical succession.
References. Cave, R. and Dean, W. T. (1959), Palaeontology 1(4), pp. 292–297, plate 53; Cave, R. (2008), Geology of the Welshpool district, BGS Sheet 151 explanation; Davies (2025), BGS OR/25/018, section 2.2.2, pp. 85–87.
SAFETY
Wear footwear with good grip on muddy, root-covered paths. Steep wooded slopes, old quarry edges and loose blocks are more significant hazards than the short distance from the road might suggest. Stay away from faces, undercut slopes and any woodland operations.
Tell someone your route and expected return time, and carry a charged phone. Do not split blocks on a shared trail or where fragments could strike walkers. Children require close supervision around slopes and quarry remains.
EQUIPMENT
A hand lens, camera, scale and notebook are sufficient for examining exposed moulds. Carry suitable clothing and walking footwear. Do not take heavy tools as a substitute for permission; any authorised work should be confined to the exact material and methods agreed with the landowner.
CLEANING AND TREATING
Weathered sandstone moulds can lose fine ribs and internal features through brushing or washing. Begin with a gentle dry brush on a sound surface and stop if grains detach. Wrap legally obtained specimens individually and keep the part and counterpart together.
Avoid acids, oils, vigorous scrubbing and indiscriminate glue or varnish. Further splitting should be controlled and should follow existing bedding rather than the fossil surface. Seek specialist advice before preparing unusual articulated material or potentially important specimens.
IDENTIFY YOUR FINDS
Need help identifying a fossil? Share clear photos, where you found it and its size with the community.
FURTHER READING
BGS: Geology of the Welshpool district
Cave and Dean’s 1959 study of the brachiopod material
BGS: revised Lower Palaeozoic stratigraphical framework
Glyndwr’s Way: Llanwddyn to Welshpool route information
ACCESS RIGHTS
Follow Glyndwr’s Way and current route notices. A public footpath permits passage along its route; it does not itself grant permission to enter adjoining woodland, visit old quarry faces, remove loose blocks or split rocks.
Ask the relevant landowner or manager before collecting or leaving the permitted route to examine material. Current collecting conditions and rights along the side paths have not been established. The former suggestion that blocks a few metres from the path could be taken or worked should not be treated as permission. Where collecting has not been agreed, leave specimens in place and photograph them.
It is important to follow our ‘Code of Conduct’ when collecting fossils or visiting any site. Please also read our ‘Terms and Conditions‘
Joe Shimmin. Last inspected 2008, Updated 2017, Edited by Jon Trevelyan 2016
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