Saturday, 18 May 2013
The stones we are currently interested in, as a means of sorting out this Rhosyfelin business, are 32c and 32d. both of whiuch are invisible in the photo on the left because they are beneath the turf. The little bluestone we can see, behind the trilithon at top left, is stone 33. There are three buried stumps in the vicinity, approx on the circumference of the bluestone circle (if there ever was such a thing). As indicated in previous posts, 32e (the one closest to stone 33) is probably a dolerite, but the other two look from the old Atkinson photos as if they are flaky and friable, and we need to know if one or both of them happen to be made of the same type of rhyolite as that represented in lots of fragments in the Stonehenge layer. If they are, we may assume that the debris or debitage has come from the destruction of one or two stones that were previously prominent standing stones. If they are NOT the same, when examined by the geologists, all sorts of other interesting possibilities open up.......
It's good to know that a number of senior archaeologists are now quite attracted by the idea of a small "keyhole surgery" operation designed to take samples adequate for the making and analysis of thin section slides. Why doesn't EH take the initiative and instigate this work? In my view this should be the current number one priority at Stonehenge. So please, EH, if you are listening, go for it! The damage to the monument would be minimal, and the work would take less than a day. We know exactly where the stumps are. I think it would be a mistake to wait for this work to be done in the context of "the next Stonehenge dig" -- whenever that might be. Big digs take a long time to fund and organize; the consent process is convoluted; and what is a very simple research objective might get caught up and even obscured in some larger project designed to answer other unrelated archaeological questions.
So forget about the archaeology. This is a simple piece of geology we are talking about. Go for it, EH! No doubt Messrs Ixer and Bevins are waiting for your call.......
Thursday, 9 May 2013
NASA satellite image of the fjord country of NE Greenland. Click to enlarge.
There is extraordinary clarity -- just a few wisps of cloud, and remarkably little ice in the fjords as well. This must be late summer -- maybe early September -- before the autumn snows start and before the sea ice moves back in to block off access into the fjords.
When I was working here in 1962 we had long spells of extraordinary hot weather -- this area is often called "The Arctic Riviera" because it is bounded by the ice sheet to the west and the pack-ice belt to the east -- both of which have the effect of blocking off frontal weather conditions. The only time in my life that I have suffered from heat stroke was in East Greenland in 1962...... and a couple of my colleagues also went down with the effects of poisoning from accumulated mosquito bites.
Above: Bedd yr Afanc passage grave (what's left of it)
Below: the fortified "settlement platform" at Carn Alw
Castell Mawr hillfort / enclosure. An Iron Age settlement site with origins in the Neolithic?
Bedd yr Afanc passage grave
Castell Llwyd promontory fort (Iron Age?) on a spur above the Nevern river
Small unnamed fort on a spur above the river near Felin y Gigfran (Penybenglog group)
Castell Henllys Iron Age "village" (National Park visitor site)
Waun Mawn standing stones -- Bronze Age?
Carn Alw complex settlement traces -- Bronze Age and Iron Age
Carn Goedog -- traces of Bronze Age (and Neolithic?) settlements on the slope beneath the crags
Pentre Ifan cromlech -- Neolithic
Tycanol Wood -- assumed Iron Age fortified site
Foel Drygarn Bronze Age cairns inside an Iron Age fortified site
Carn Ingli Iron Age hillfort and abundant traces of Bronze Age / Iron Age settlement on the common
Nevern Castle -- Iron Age and maybe earlier traces beneath the medieval fortifications
Assorted standing stones -- assumed Bronze Age
Carreg Coetan cromlech, Newport. Neolithic.
Eglwyswrw motte and bailey -- on an Iron Age site?
Settlement near Cwmgloyne -- Iron Age?
Caer, Bayvil -- Iron Age fortified site?
Trafael cup-marked stone -- Neolithic cromlech?
Crugiau Cemaes barrow cemetery -- Bronze Age
There is more info about some of these sites here:
and much, much more in Neil Figgis's excellent guide called "Prehistoric Preseli".
What we see across this landscape is a long history of continuous settlement, with many sites modified from one archaeological era and into the next. Some sites have been used off and on for maybe 5,000 years, and they show that the landscape and its resources were capable of maintaining a small population which had some unique characteristics (for example, there is much debate about the "Nevern Valley" group of chambered tombs and their cultural associations....)
I know most of these sites pretty well, and I am not aware of any site to which stones have been hauled from somewhere else. The stones used are ALWAYS local -- and while there is some doubt about the origin of the Trefael Stone, that is almost certainly an erratic picked up and used more or less where it was found. Nor is there any evidence of stone colour or texture mattering in the least -- I cannot see any evidence of some stones being preferred above others. The message is that the people who built all these monuments -- ranging across the Neolithic, Bronze Age and Iron Age -- were entirely disinterested in both the origins of the stones used, and the nature of those stones.
The second key point is that in a moderately well settled community such as that of the Nevern Valley and its tributaries, there must have been considerable seasonal movement between the woodlands in the valleys and the open pastures of the Preseli Hills and Mynydd Carningli -- and even the spurs of Carnedd Meibion Owen, Waun Mawn and Frenni Fawr. That means that people were travelling, hunting and camping -- and later on moving about with domesticated animals as well. Trade, raiding expeditions, and transhumance would all have played a part. In that context, it would not be at all surprising that traces of temporary encampments would have been found at Rhosyfelin -- it is a perfect sheltered location with a handy ford across the river, probably grazing for animals on the meadows of the flood plain, and maybe even hunting to be had in the wooded valley itself. Fish traps and animal traps might well have featured. I would hazard a guess that Rhosyfelin Camp -- and maybe scores of other river valley locations in the area -- were used from Mesolithic times right through to the Roman period.
So was Rhosyfelin an important place? I doubt it. Was it a site for a bluestone quarry, linked to Stonehenge? You must be joking.......
It is one of the extraordinary features of glacier ice that it can in some circumstances erode more or less vertically down into solid rock, and in other cases flow across a wide open landscape, cleaning it up and scouring the rock surface clear of debris.
These two pictures show the extremes. The top one is a new photo of Torres del Paine in South America, where streaming ice in a high mountain landscape has cut a series of vertical-sided troughs. Gradient and glacial bed conditions have something to do with it -- and if there is a very dynamic situation with high accumulation, rapid movement and evacuation, and high melting rates lower down, the resultant glaciated landscape will be spectacular indeed.
In other cases, as in the Vestfold Hills area of Antarctica (shown in the lower photo) very slow ice movement in a polar glacier context may just grind away the land surface inexorably over millions of years. There are a few patches of ancient till here, but the areally scoured rock surface is remarkably clean. There are many ancient freshwater lakes here -- most of them frozen solidly almost down to their beds because of the extremely low temperatures experienced in the locality. Look at the extraordinary patterns on the rock surface. These are basalt dykes -- hundreds of them......
Wednesday, 8 May 2013
Click to enlarge-- there is fantastic detail on the image.
You might think that this is a wonderful image of glaciated terrain. Think again. It's an image of an island in close proximity to the edge of the Greenland Ice Sheet, and indeed there are huge outlet glaciers draining into Wolstenholme Fjord -- but this island bears precious little evidence of glaciation. If you look carefully you can see that the snow cover is just a seasonal one-- much of it less than a metre thick. This is an ice-free island. If you want to see what it looks like in the summer, use Google Earth. Look too at the valleys -- these are fluvial valleys, with typical V-shaped cross profiles as distinct from the U-shaped cross profiles typical of glacial troughs. This is essentially a piece of an ancient river-eroded plateau bounded by steep coastal cliffs.
The feature in the foreground is a raised marine foreland at the NE tip of the island -- you can see the steps caused by intermittent isostatic uplift since the end of the Devensian glacial stage. I'm not sure how high the raised marine limit is in this area -- but it is probably well over 100m above present sea-level. Back in 1962 I studied similar features in a raised delta in Kjove Land, East Greenland. Happy days......
Sunday, 5 May 2013
This is an excellent photo of the top of the Stonehenge Layer and the section cut through it during the 2008 excavation by Profs Wainwright and Darvill (Photo credit: Tim Darvill).
For those who may not be familiar with the report on the 2008 excavations, here is a short extract. There is no reason to think that we are looking at anything other than a highly variable deposit laid down over a long period of time -- maybe as much as 5,000 years -- and containing much evidence of human interventions.
The Antiquaries Journal, 89, 2009, pp 1–19 r The Society of Antiquaries of London, 2009
doi:10.1017⁄s000358150900002x. First published online 21 April 2009
STONEHENGE EXCAVATIONS 2008
Timothy Darvill, VPSA, and Geoffrey Wainwright, PSA
Well, the Stonehenge Layer itself turned out to be quite a complicated set of deposits. It is a body of material that has accumulated over quite a long time. Looked at in section it is quite mixed, and we treated it, as I said, as a series of plano levels or spits that we could take apart. Work is still progressing on the analysis of that material, but patterns are already beginning
Looking at the geochemistry, for example, there are discrete concentrations across spit
1 of pH, magnetic susceptibility, copper, iron, phosphorous, magnesium and potassium,
all indicating various localized activities in that deposit. It implies quite small-scale and
discrete deposition of materials and events, even within the small area that we were
examining. Some of those things go right down through the Stonehenge Layer, and some
don’t. In the second spit, for example, we see that copper remains the same, while
magnetic susceptibility changes, and as we go down to the third level, again, some things
hold, some change. It thus seems that we have a whole series of overlapping and intercutting
events within the Stonehenge Layer.
We are still taking that soil apart, and there is a good deal more to do, but we have a
series of artefacts from the Stonehenge Layer – for example, a traditional late Neolithic
asymmetrical arrowhead, a flint hammer that has been used for breaking up stones, two
iron wedges, which have also been used for breaking up stones (they are quite small
wedges) and a human tooth from immediately below the turf.
So, in summary, the Stonehenge Layer is a heterogeneous deposit some 350mm thick.
It has multiple localized spreads of material, with soil stabilization and worm sorting
going on. There is a lot of mixing, and a lot of disturbance in there. There is bluestone
and sarsen in quite some quantity. The bluestone outnumbers the sarsen numerically.
Both types of stone were scattered right through the deposit, but there are several localized
concentrations of broken bluestone.
There is direct evidence of stone breaking in the Stonehenge Layer. The vast majority
of pieces constitute struck or deliberately detached flakes, rather than being simply
random bits of material. They accumulated, as far as we can tell, over a long period –
probably from prehistoric times onwards. Our provisional interpretation is that what we
are looking at is essentially stone robbing, the breaking up of the monument, over a long
period, rather than stone shaping before its construction. We will see as we go on with
further analysis of the material whether this interpretation holds up, but that seems to be
what we are seeing at the moment.
Time for a re-focus onto stumps 32c and 32d. These are the two stumps shown in the Atkinson excavation photos above (from the EH site) -- and which are now very much in the frame following the most recent geological work on the Stonehenge rhyolitic debitage. (Note: there have been various mistaken identifications of stump 32e as being made of rhyolite -- that's the stone closest to Atkinson's head in the lower photo. It doesn't look at all like a rhyolite, and it is almost certainly a dolerite -- either spotted or unspotted.......)
The lower photo shows that the stump (32d) at bottom left has a distinctly laminated, foliated and flaky appearance, and many of us have commented on the fact that it has a distinct visual resemblance to the stones revealed during the MPP excavations at Rhosyfelin. That appears to be a good candidate for having come from Rhosyfelin or somewhere in that neighbourhood.
In the top photo we can see that stump 32c looks very similar to stump 32d, but the definition in the photo isn't as clear as it might be.........
I have dealt with this topic in oprevious posts:
So this is the interesting question: HAS THE BULK OF THE RHYOLITIC DEBITAGE FOUND IN THE STONEHENGE ENVIRONS (AND IDENTIFIED BY BEVINS AND IXER AS HAVING A PROBABLE SOURCE AROUND RHOSYFELIN) COME FROM THE DESTRUCTION OF STONE 32C, 32D OR MAYBE BOTH OF THEM?
There is a reasonable chance that the answer to that question is "yes" -- but at the moment there are apparently no physical samples in existence which will allow a match to be made. So here is a plea to English heritage: in the interests of science, will you please allow the geologists to undertake a spot of "keyhole surgery" into the turf (the stumps are only just beneath the surface) and to take small samples of stumps 32c and 32d for analysis? That should be a very simple task, since the precise locations of the stumps are known -- and the research benefits would be out of all proportion to the amount of "damage" that might be done.