Not From Northeast Scotland At All

A bold claim buried inside a methods dispute — and what happens when you check whether the follow-up paper answered it

Ciborowski and Nash's reply to Pearce et al. (2026) is, on its face, a defence of an arithmetic similarity method against a comment paper — the subject of the previous post. But in the course of that defence, almost as a side point in their Altar Stone discussion, the authors make one of the more consequential claims to appear anywhere in this literature. Discussing the U–Pb zircon evidence behind Clarke et al. (2024)'s Scottish attribution, they write:

"...the more valid conclusion that may be drawn from the U-Pb zircon data in Clarke et al. (2024) is that, even with five comparator analyses, none of the individual 'Altar Stone' samples look anything like the Orcadian Basin in terms of U-Pb zircon geochronology. This observation alone suggests that the Altar Stone is not from northeast Scotland.

That is the least hedged sentence in the entire reply. Everywhere else, Ciborowski and Nash are careful to say their arithmetic method makes no provenance determinations of its own. Here, discussing someone else's data, they drop that caveat and state a direct conclusion: on their reading, the Altar Stone may not be from the Orcadian Basin, or northeast Scotland, at all.

The argument

Clarke et al. (2024)'s Scottish attribution rests on comparing a U–Pb zircon age signature for "the Altar Stone" against a signature for "the Orcadian Basin." Both are aggregates. The Altar Stone signature is a pooled dataset built from three separate debitage samples — 2010K.240, FN593 and MS3. The Orcadian Basin signature is a pooled dataset built from five separate Old Red Sandstone samples (Strachan et al. 2021's RS-ORS-14 to RS-ORS-18), drawn from different formations spanning thousands of metres of stratigraphy across hundreds of square kilometres.

Ciborowski and Nash break both pools back into their constituent samples. Their finding: the three individual "Altar Stone" samples show different age-distribution shapes from each other, and the five individual "Orcadian Basin" samples likewise disagree with each other. If a pooled Altar Stone signature only resembles a pooled Orcadian Basin signature because averaging together internally inconsistent groups smooths out their disagreements, the resemblance between the two pooled signatures may not indicate a shared origin at all — it may simply be an artefact of aggregation.

Does the newer paper answer this?

The obvious question is whether Clarke et al.'s more recent paper — Clarke et al. (2026), "From Highlands to Henge," which refines the search to individual candidate outcrops within the Orcadian Basin and reports Sarclet as the strongest statistical match (p = 0.96) — addresses this aggregation problem. It does not. Checking the paper directly, its Methods section states:

"We use the reported Altar Stone zircon U–Pb concordia dates from Clarke et al. (2024), which are compiled from three thin sections: MS3, 2010k.240 and FN593."

The refinement in the 2026 paper is entirely on the source side of the comparison: instead of testing one basin-level "Orcadian Basin" aggregate, it tests five individual outcrop samples (Sarclet, Braemore, Kirtomy, Portskerra, New Aberdour) separately against the Altar Stone. But the Altar Stone side of every one of those five comparisons is still the same pooled, three-sample aggregate from 2024 — the exact aggregate Ciborowski and Nash's reply argues conceals internal disagreement. The celebrated Sarclet result (p = 0.96) is a match between one individual outcrop and an unexamined pool of three debitage samples, not a match against any single physical fragment of the Altar Stone.

This is not a case of Clarke et al. considering the aggregation critique and rejecting it. The timeline rules that out: "From Highlands to Henge" was accepted for publication on 2 May 2026, while the Ciborowski and Nash reply was not accepted until 11 August 2026. The critique postdates the paper it would apply to. As things stand, it is simply unanswered.

What this means for the East Caithness screening work

The Ba/Rb stream-sediment screen published on this blog cites the Sarclet zircon match as independent corroboration: two methods sharing no data, assumptions, or statistical framework converging within about 10 km of one another. That convergence claim is unaffected in its own terms — the stream-sediment screen does not depend on the zircon data being sound. But the corroborating value of the zircon match itself now rests on a result that a live, unaddressed critique says may be a statistical artefact of pooling three internally disagreeing samples. Section 3.5 of the screening paper should be caveated accordingly: the Sarclet convergence is worth noting, but it leans on a comparison whose Altar Stone side has not yet been tested sample-by-sample against Sarclet or any other candidate outcrop.

The natural next test, if the underlying per-sample zircon age data from Clarke et al. (2024) are available, is to rerun the Sarclet comparison three times — MS3 alone, FN593 alone, 2010K.240 alone — rather than pooled. If any individual sample still matches Sarclet at a comparable significance level, the convergence claim would be substantially strengthened. If none does, or if the three samples point in different directions, the aggregation critique would carry through into the specific result this blog has relied on, and the independent-convergence argument in the screening paper would need to be withdrawn or significantly qualified.

The rest of the reply, briefly

The remainder of Ciborowski and Nash's reply is a narrower methods dispute, covered in more detail in the previous post. In short: they concede three points to Pearce et al. (2026) — that rounding has an outsized effect on ratios calculated from silcrete's very low trace element concentrations, that the Certified Reference Materials used in the original sarsen analyses (Nash et al. 2020) were not ideal, and that weighting element ratios by analytical precision would improve their method. They dispute the framing of the rest of the comment as a straw man, defend the use of trace element/Zr ratios against raw concentrations for silcrete provenancing, and argue that Pearce, Bevins and Ixer's own past work (assigning non-spotted dolerite debitage to the spotted dolerite source Carn Goedog using geochemistry alone) is inconsistent with their criticism of a similar inference in Ciborowski and Nash's own paper regarding Stone 62.

State of the debate

Year	Paper	Main development
2020	Nash et al., Science Advances	West Woods proposed as sarsen source.
2024	Clarke et al., Nature	Orcadian Basin proposed as Altar Stone source, via pooled zircon comparison.
Early 2026	Ciborowski & Nash	Arithmetic similarity method proposed.
June 2026	Pearce et al.	Comment disputing the arithmetic method.
June 2026 (accepted 2 May)	Clarke et al., J. Quaternary Sci.	Sarclet identified as strongest individual-outcrop zircon match (p = 0.96); Altar Stone side of comparison left pooled.
July 2026	Daw	East Caithness Ba/Rb screen; cites Sarclet zircon match as independent corroboration.
September 2026	Ciborowski & Nash	Reply: disputes the comment's framing, and separately argues the disaggregated zircon evidence may not support a northeast Scotland source at all.

References

• Ciborowski, T. J. R., Nash, D. J. 2026. "Arithmetic Methods for Exploring Archaeological Source Provenance Using Geochemistry – A Reply to Pearce et al." Journal of Archaeological Science: Reports 75: 106012.
• Clarke, A. J. I., Kirkland, C. L., Bevins, R. E., Pearce, N. J. G., Glorie, S., Ixer, R. A. 2024. "A Scottish Provenance for the Altar Stone of Stonehenge." Nature 632: 570–575.
• Clarke, A. J. I., Veness, R. L. J., Kirkland, C. L., Clark, C. D., Gandy, N., Emery, A., Bradley, S. L., Ely, J. C., Ádám, I. 2026. "From Highlands to Henge: Refining the Provenance and Transport Pathways of Stonehenge's Altar Stone." Journal of Quaternary Science, 1–8.
• Daw, T. 2026. "A Multi-Element Geochemical Screen, Verified Against Bedrock Geology, for the Source of the Stonehenge Altar Stone Within the Orcadian Basin." sarsen.org.
• Pearce, N. J. G., Bevins, R. E., Ixer, R. A., Pirrie, D. 2026. "Arithmetic Approaches Alone Are Inadequate in Defining Similarity: A Comment on Ciborowski and Nash 2026." Journal of Archaeological Science: Reports: 105874.
• Strachan, R. A., Olierook, H. K. H., Kirkland, C. L. 2021. "Evidence from the U-Pb-Hf Signatures of Detrital Zircons for a Baltican Provenance for Basal Old Red Sandstone Successions, Northern Scottish Caledonides." Journal of the Geological Society 178.