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Saturday, 19 May 2018

Blanket peat on Waun Mawn

Exposure in the side of one of the drainage channels on Waun Mawn, on a gentle south-facing slope.  Here we see about 30 cm of iron-stained / gleyed regolith made of broken meta-mudstone debris with signs of cryoturbation.  Above that there is a thin layer with streaks of organic material, and above that about 10 cm of "blanket peat" containing a network of roots from the present-day turf layer at the surface, which is only 5 cm thick.  This is quite typical of the moorland hereabouts.  There is no sign of Devensian till at this location.

I have been taking another look at the "progress report" written by Prof MPP for the Rust Family Foundation:

In the section on Waun Mawn some stress is placed on "the date of peat formation" as a guide to the age of the sockets and the speculations surrounding stone removal.

As far as the biggest recumbent stone in the putative "proto-Stonehenge" circle is concerned, MPP says this: Its former stone socket is lined with many packing stones, and the peat fills of this socket indicate that the stone fell after the onset of peat growth."

On the other hand, "The smaller recumbent stone excavated in 2017 is on the east end of the arc and is just under 1m long (fig.4). The fill of the stone socket contains only brown loam and no peat, indicating that it filled before the growth of peat. Thus this stone came down before peat growth."

Then again:  "Emptied stone sockets with stone packing (but no surviving monolith) were identified beyond both ends of the arc of monoliths. The socket on the west side was a circular pit (0.85 m- diameter and 0.3 m-deep) containing large packing stones set vertically. The emptied socket had filled with brown soil before any peat formation. Deformation of the edge of the pit showed that its former standing stone had been removed towards the north."
"We discovered two empty stone sockets on each end of the arc, suggesting that these stones may well be the remains of a dismantled stone circle (figs.5,6). Megaliths were removed from these sockets before the onset of peat growth on this site, indicating that the stone
circle was dismantled in the distant past."

Tying things up and seeking to demonstrate (even at this very early stage) that there WAS indeed a stone circle here, on the basis of very scanty evidence, MPP concludes:  "It can be assumed that the lack of peat in three of the stone sockets indicates that their standing stones were removed before the growth of blanket bog. This is likely to have started growing around 3,000 years ago, which would indicate that the stones came down in the Neolithic or earlier Bronze Age."

This is all seriously confusing.  MPP suggests that blanket peat formation here did not start until 3,000 years ago, which would place it in the Sub-Atlantic climate phase (pollen zone VIII), well after the elm decline and 3,000 years later that the date normally assumed for blanket peat development in the uplands of Wales.  In most of the texts and in Gallego-Sala et al (2015) it is suggested that in upland Wales blanket peat development probably started early -- maybe as early as 7,000 years ago --  during the Atlantic "climatic optimum" when it was warm and wet.  It's also suggested that around 3,000 years ago, at a time of lower rainfall totals, and an increase in ash and birch cover, blanket peat development might actually have slowed.  After 3,000 years ago, blanket peat initiation occurred only in a smallish number of "less favoured" locations. 

In the Preseli uplands, we can reasonably assume that blanket peat development will have started at the same time as in the other uplands of Wales where there were acid soils and high precipitation rates.

Nothing seems to fit.  So we have a problem........

Could it be that the things being called "stone sockets" are not stone sockets at all, but are simply surface depressions or irregularities that have nothing whatsoever to do with standing stones?


Gallego­-Sala, A. V., Charman, D. J., Harrison, S. P., Li, G. and Prentice, I. C. (2015) Climate­-driven expansion of blanket bogs in Britain during the Holocene. Climate of the Past Discussions, 11 (5). pp. 4811­-4832.
ISSN 1814­9359 
Available at

PS.  The only detailed work on the development of vegetation in the Preseli - North Pembrokeshire area is a thesis by Philip Seymour, completed in 1985.  It can be seen here:

It's essentially a pollen analysis study based on a variety of upland and lowland suites, recording changes in pollen frequencies in sediment sequences.  It makes the point that the development of blanket peat bogs was never very great in this area, partly because of the lack of extensive plateau surfaces where waterlogging could occur.  So drainage -- mostly on gentle slopes -- was generally sufficient to prevent blanket peat development.  This is borne out by the generally thin peat layers which we find across most of the landscape -- 10 cm is a rather typical thickness.  Did all of the peat start to develop at about the same time?  And was that time associated with the Neolithic / Bronze Age increase in land clearance associated with forest burning and increased grazing activity?  Seymour suggests that this was the case, and that peat development before the Neolithic was not very marked, especially on fairly well-drained slopes.  He takes a rather anthropogenic approach, suggesting that peat and soil development was very much influenced by settlement and land use practices.  But there is a danger of circular reasoning -- was the environment causing man to make certain land-use decisions, or were cultural decisions shaping the environment?  Walker and McCarroll (in the QRA Field Guide for West Wales, 2001) take a more nuanced approach, agreeing that periods of peat development are associated with periods of increased rainfall, leaching, iron pan creation and waterlogging  -- while admitting that there is such a wide range of dates for the "onset of peat development" in West Wales that land use practices and settlement pressure must have some role to play.

It will be interesting to see what turns up when Waun Mawn is examined in greater detail.....

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