He addressed the points raised as follows:
1. I can see no evidence of any sort in your research which supports the contention that some of these individuals came from West Wales rather than any other part of Palaeozoic Britain. Have I missed something?
Apparently you have. "Those with the highest values (>0.7110) point to a region with considerably older and more radiogenic lithologies, which would include parts of southwest England (Devon) and Wales (parsimony making locations further afield – including parts of Scotland, Ireland and continental Europe – less probable).”
“While strontium isotope ratios on their own cannot distinguish between places with similar values, this connection suggests that west Wales is the most likely origin of at least some of these individuals…”
So we fully acknowledge that the Sr isotope results on their own are not sufficient to make a specific link with west Wales, and that this relies on accepting that the archaeological connection implied by the bluestones being transported by humans, which obviously you don't accept. That is a separate issue.
2. Why have you simply accepted Mike PP's contention that there are bluestone quarries in West Wales without acknowledging that there is a major dispute about the reliability of his evidence?
We chose not to enter into this debate in this paper, since it has been discussed elsewhere, and the format of this kind of paper is by its nature very brief.
3. Why have you marked Craig Rhosyfelin on Figure 2 when it has no relevance whatsoever for the data shown on the map?
It is marked as one of the proposed sources for some of the bluestones. It is also the location for some of the plant samples taken for the Sr baseline for this part of west Wales. So it has relevance for both points.
4. I can see no evidential basis for the "geographical assignments" chosen in Figure 3. The individuals chosen could just as well have come from a multitude of other places.
No, they could not have. The assignments shown on the map for the left-hand figure are the only locations in Britain that are consistent with the Sr isotope result for that particular individual (and you’ll note that the locations are not limited to west Wales), to the specified degree of confidence. These are based on spatial statistics using the most complete Sr baseline map currently available for Britain.
5. I'm not convinced by the "local" and "far travelled" designations either. Is there really any significance in your "cut-off point" of 0.7090?
"The strontium isotope ratios for modern plants clearly distinguish the Ordovician and Silurian lithologies of west Wales (0.7095–0.7120) from the Cretaceous chalk of Wessex (0.7074–0.7090), which extends for at least 15 km around Stonehenge in all directions."
The use of a 0.709 upper cut-off for the Cretaceous Chalk is if anything rather conservative, as no values this high on plants have been reported. We can and do support its significance using spatial statistics as reported in the paper and in supplementary information. A comparable range has been used in other strontium isotope studies in the Stonehenge region.
6. The isotope ratios for modern plant materials from West Wales -- why are there apparently no controls from other sites as well? This is another example of a strong -- and very unfortunate -- bias in the research.
This is inaccurate. We used the most up to date Sr baseline map available for Britain, from Evans et al. 2010 with additions. This provides the characterisation (‘controls’) for the rest of Britain shown in Figure 2, with the right hand side showing the corresponding uncertainty, which takes into account the lower sampling resolution of many parts of Britain. We specifically sampled and measured additional plants from west Wales to be able to characterise that area more thoroughly and thus better understand the range of variation there. We also provide new values from the Berkshire Downs to the north, bordering the Vale of the White Horse, obtained as part of another project, but again supporting the cut-off value of 0.7090 for the Chalk.