A new paper sources Yorkshire's Devil's Arrows to Brimham Rocks, 18 km west. The zircon evidence for that is sound, but the stratigraphy behind it needs a correction, and the case against glacial transport is stronger than the paper itself makes it.
Clarke, Leary and Kirkland have a new paper in Proc. R. Soc. A (20260504). Peel samples were taken from the three standing stones at Boroughbridge, and roughly a kilogram of rock each from Brimham Rocks and Plumpton Rocks. Detrital zircon U–Pb ages from the Arrows match Brimham (Kolmogorov–Smirnov p = 0.77) and do not match Plumpton (p = 6.7 × 10–5). Historic England's long-standing attribution to Plumpton is the wrong outcrop.
That result stands. The stratigraphic framing around it does not. The paper describes Brimham and Plumpton as "both Upper Plumpton Grit outcrops... the same Namurian stratigraphic interval." The British Geological Survey's own lexicon says otherwise, and checking it against the 1:50k mapping changes what the zircon match is actually evidence for.
What they actually dated
The Devil's Arrows stand on Triassic Sherwood Sandstone and are not made of it — the paper establishes this cleanly, on both lithology and zircon spectrum, and it isn't in dispute. What they are made of is Kinderscoutian Millstone Grit, deposited around 318 Ma by the Pennine river system. The paper states that its two comparison outcrops, Brimham Rocks and Plumpton Rocks, "are both Upper Plumpton Grit outcrops... the same Namurian stratigraphic interval." Checked against the field literature for each site individually, that statement is wrong, and it's wrong for reasons independent of each other — the two outcrops aren't misidentified by the same error, they're simply two different units.
Brimham. BGS's own excursion guide to the site, describing the rock as sampled in the field rather than as read off a map, states that "the spectacular natural cliffs and tors of Brimham Rocks are carved out of a plateau of Lower Brimham Grit (mid-Namurian)." Soltan and Mountney's 2016 study of the outcrop's channel architecture — a paper Clarke, Leary and Kirkland themselves cite, for basin-scale heterogeneity — captions their own photograph of the site the same way: "Lower Brimham Grit succession exposed at Brimham Rocks." The BGS lexicon records Lower Brimham Grit under the alternative name Lower Plompton Grit (LPG), part of the Hebden Formation, sitting above the Ure Shell Bed and below the Eccup measures. Three independent descriptions, converging on the same unit: Brimham Rocks is the Lower leaf.
Plumpton. The BGS memoir for the Harrogate sheet (62) puts its cover photograph exactly where the dispute sits: Lover's Leap, Plumpton Rocks, captioned as "naturally sculptured crags of Upper Plompton Grit at its type locality." Plumpton Rocks isn't merely similar to the Upper leaf — it's the section BGS uses to define it. Cooper's Knaresborough Gorge excursion notes, and the Denys Smith memorial trip report covering the same ground, both describe the Lower Plompton Grit as exposed separately, a few kilometres away at Knaresborough Gorge, beneath the Upper leaf in the local succession, not at Plumpton Rocks itself.
So the two outcrops the paper compares are the lower and upper leaves of the Plompton Grit, divided by the Eccup Marine Band — not, as stated, the same stratigraphic interval. This isn't a map-reading disagreement over which of two adjacent colours a dot falls in; it's the paper's named comparison localities being described, independently and repeatedly, as different units in the literature it already draws on for other purposes. It also isn't an incidental distinction. The Hebden Formation's lower part is "a turbiditic facies... with laterally impersistent and locally thick, massive, coarse to very coarse-grained sandstones" — channelised, not a blanket sand — while the upper part is "sheet-like, laterally persistent." Individual channel bodies of that kind can carry genuinely distinct detrital zircon signatures, which is the mechanism the paper needs for Brimham and Plumpton to differ in the first place. Correcting the stratigraphy doesn't weaken the zircon result — Arrows vs Brimham, KS p = 0.77; Arrows vs Plumpton, p = 6.7 × 10–5 — it explains it.
Plumpton Rocks — the outcrop the paper samples and compares against — is consistently described in BGS excursion literature (Cooper and Burgess's 1993 Harrogate memoir, and the published Knaresborough Gorge excursion guides) as the Upper Plompton Grit. So the two sampled outcrops are not "the same Namurian interval": they are the lower and upper leaves of the Plompton Grit, separated by the Eccup Marine Band. The paper's own Kolmogorov–Smirnov numbers already say this — Arrows vs Brimham not significantly different, Arrows vs Plumpton clearly different — the caption just doesn't correctly name why.
The place is Plumpton Rocks, with a U, used throughout the paper and by Historic England. The adjacent park and houses are Plompton as is the geological unit Plompton Grit, with an O, Both the Lower and Upper leaves carry it: LPG and UPG. Reading "Plumpton Rocks" against "Plompton Grit" without noticing the two are spelled differently makes it easy to miss that the lexicon is also carrying two separate codes under that name, not one.
It also isn't an incidental distinction. The BGS lexicon's lithological description of the Hebden Formation splits it into a lower part — "a turbiditic facies... with laterally impersistent and locally thick, massive, coarse to very coarse-grained sandstones" — and an upper part of "sheet-like, laterally persistent" sandstone. The Lower Brimham/Plompton Grit is channelised, not a blanket sand. Individual channel bodies of that kind can carry genuinely distinct detrital zircon signatures, which is the mechanism the paper needs for Brimham and Plumpton to differ in the first place. Correcting the stratigraphy doesn't weaken the zircon result; it explains it.
Click to enlarge
BGS Geology 50k bedrock + superficial, © UKRI 2026. Frame BNG 415–445 E, 448–500 N km.
The map
The 50k sheet covering Brimham, Boroughbridge and Plumpton (dots are GetFeatureInfo point samples, not filled polygons) shows the Lower Brimham/Plompton Grit at outcrop in one cluster: the Brimham Moor tor field and the ground immediately west of it. The same leaf reappears elsewhere on the sheet, but under cover — beneath Devensian till north of Hack Fall, and beneath Vale of York Formation roughly 12 km west of the Arrows — rather than exposed. The Upper leaf is a separate storey above it.
A closer inset around Plumpton shows both leaves printed in the same yellow on the standard 50k colour scheme, distinguished only by lexicon code: Lover's Leap itself sits on Upper Plompton Grit (UPG), with a strip of Lower Plompton Grit (LPG) — the same unit as Brimham and the Arrows — running immediately to its west, separated by thin intervening measures. That strip was not sampled.
6 × 6 km, BNG 432–438 E, 450.5–456.5 N. Same WMS yellow, two lexicon codes.
What the air photos add
Brimham Moor is an open plateau of exposed stacks — individual joint blocks, already the size of pillars, visible from the path and from the air (Geograph squares SE2064 and SE2065). Plumpton, by contrast, is a lake set in woodland with a single crag along one shore — Lion's Den, Lover's Leap, Needle's Eye — roughly 10–12 m above the water, part natural and part quarried, matching Historic England's listing description. The fields west of the lake, where the 50k map places the Lower Plompton Grit at outcrop, are smooth pasture with no visible scatter of grit blocks.
| Place | What the air photo shows | Leaf | Plausible as a stone source |
|---|
| Brimham Moor | Open plateau of stacks | Lower (LOBM/LPG) | Yes — blocks already detached along natural joints |
| Plumpton lake crag | One wooded cliff, 10–12 m, part quarried | Upper (UPG) | Wrong leaf on the zircon evidence; already excluded |
| Fields west of the lake | Smooth farmland | Lower (LPG), per the map | Not visible as exposed rock from the air |
Brimham Rocks, "Idol Rock" — Penny Mayes, Geograph 1184, CC-BY-SA 2.0.
Against glacial transport
Late Devensian ice in the Vale of York moved NNW to SSE, down-valley — the wrong direction to have carried anything off the Pennine edge onto the Boroughbridge ridge, and no reconstruction maps a westerly conveyor off Brimham Moor at all. The excavated stone sockets — 1.5 m deep, flat-bottomed, and of matching dimensions at all three stones — already show the row was set by hand, not left in place by melting ice. Two further lines point the same way: the Arrows carry deep, weathering-fluted grooves and an elongate, naturally joint-bounded shape matching Brimham's own fracture pattern (fig. 6B), not the rounding expected of a boulder that has travelled inside moving ice; and all three stones share a single, statistically indistinguishable zircon population (table 1), closer to what one quarried outcrop produces than to the mixed assemblage typical of glacial till.
Once human erection is established — and the sockets establish it regardless of source — the question of transport is no longer whether people moved the stones, only how far. A group that can lever a pillar off a joint face and walk it into a socket a hundred metres away has already demonstrated the method; eighteen kilometres from Brimham is a longer version of the same task, not a different one. Glaciation, by contrast, still needs an ice path the reconstructions don't map, and still leaves the fluting, the jointing and the single-source signature unexplained. What the ice-flow reconstructions cannot do, and the paper's own discussion concedes, is resolve or exclude a specific 18 km path between Brimham and Boroughbridge at the resolution the abstract implies — but by that point glaciation has already lost the argument on capability, and an unresolved ice model doesn't reopen it.
What still needs checking
Three things follow directly from the mapping and are not addressed in the paper:
- The Lower Plompton Grit strip immediately west of Lover's Leap — the same unit as the Arrows on the 50k map, closer to Boroughbridge than Brimham, and neither dated nor visibly exposed as a tor field from the air.
- Whatever Carboniferous sandstone actually lies at or near surface roughly 12 km west of the monument, under the Vale of York Formation.
- A second storey at Brimham itself — Soltan and Mountney (2016) already log two distinct channel systems within the tor field, which the single 1 kg sample cannot distinguish between.
Until those are checked, Brimham is the best-supported source among the outcrops that have actually been dated, not a uniquely identified quarry. The zircon evidence is good enough to rule out Plumpton and rule out the local Sherwood Sandstone; it is not yet enough, on its own, to rule out the other exposures of the same facies belt that lie closer to the monument and were never sampled.
References
- Clarke, A.J., Leary, J. & Kirkland, C.L. 2026. Deliberate prehistoric sourcing of the Devil's Arrows, Britain's tallest stone row. Proc. R. Soc. A 482, 20260504. doi.org/10.1098/rspa.2026.0504
- BGS Lexicon of Named Rock Units: Hebden Formation (HEBD); Millstone Grit Group (MG).
- BGS Lexicon: Lower Brimham Grit (LOBM) / Lower Plompton Grit (LPG).
- BGS Earthwise. Carboniferous rocks of upper Nidderdale — an excursion, Locality 1, Brimham [SE 212 670].
- Cooper, A.H. 2008. Permian and Carboniferous, Knaresborough — excursion notes. Denys Smith Memorial Trip, BGS Open Report OR/08/044.
- Soltan, R. & Mountney, N.P. 2016. Interpreting complex fluvial channel and barform architecture: Carboniferous Central Pennine Province, northern England. Sedimentology 63, 207–252.
- Cooper, A.H. & Burgess, I.C. 1993. Geology of the country around Harrogate. Memoir, sheet 62.
- Wilson, A.A. & Thompson, A.T. 1965. The Carboniferous succession in the Kirkby Malzeard area. Proc. Yorkshire Geol. Soc. 35, 203–227.
- Bateman, M.D. et al. 2015. Last glacial dynamics of the Vale of York and North Sea lobes.
- Clark, C.D. et al. 2022. The BRITICE-CHRONO reconstruction. Boreas.
- Historic England NHLE 1014705, Devil's Arrows.
- Historic England NHLE 1000535, Plumpton Rocks.
Contains British Geological Survey materials © UKRI 2026. Geograph photographs CC-BY-SA as credited on source pages.
