THE BOOK
Some of the ideas discussed in this blog are published in my book called "The Bluestone Enigma" -- available by post and through good bookshops everywhere. Bad bookshops might not have it....
To order, click
HERE

Sunday, 31 March 2013

Those "periglacial" stripes -- solutional rills?


This is a still from the recent TV film which we have already discussed at length.  It's a somewhat fanciful artistic representation of the two famous "periglacial stripes" which, according to MPP,  led Stonehenge to be created here rather than somewhere else.  the trouble is that there are not just two of them.  Photos show that there are scores of them, quite close together, meandering slightly and with ridge crests often about 50cm above the trough bottoms. 

I have already shown this map of the contours around Stonehenge:


Unfortunately, it doesn't show the detailed contours (25 cm interval) for the key part of the Avenue, so all we have to go on are the comments from Charly and Mike that the "grooves" or stripes do not run directly downslope, but DIAGONALLY.  This seems to be confirmed on this LIDAR image which I recently came across, in the Field and Pearson Stonehenge Report from 2011.


If you look very carefully at the "grain" showing up on the image (click to enlarge) you'll see that the Avenue is aligned a few degrees away from the direct downslope orientation.

One would need to examine these troughs and ridges quite carefully to try and work out their origins (Simply to call them "periglacial stripes" is highly misleading, since it tells us nothing about the actual PROCESSES involved.)

My money is still on these stripes, which may cover a large part of the landscape beneath the regolith or soil layer, being solutional rills which owe their orientations partly to some structural control in the chalk bedrock.  It may be that the presence of a permafrost table might have played a part in this, by preventing the downward passage of surface water and concentrating flow close to the ground surface but maybe within the soil layer.  Much more work to be done -- but please can it be done by a geomorphologist rather than an archaeologist?

Source of image:

Research Report Series 105-2011
STONEHENGE WORLD HERITAGE SITE
LANDSCAPE PROJECT
STONEHENGE DOWN AND THE TRIANGLE
ARCHAEOLOGICAL SURVEY REPORT
David Field and Trevor Pearson



66 comments:

ND Wiseman said...

Hi Brian
--> Confused Person <--
Though I was a proponent of the "Ice Striations" long before they were elevated to their present trendy popularity, I have not seen them in any Geophys imagery or in the LiDAR.
I do see plough-marks, and lots of them.

Are these the marks to which you refer in the provided image?

I certainly agree that there are several more than 2 Striations, but they do tend to usher the Avenue through much of its straight run. So I'm not sure I understand what you mean about the knoll's downslope being slightly opposed to the Avenue.

I suspect that the upslope approach to Stonehenge was one reason that the Ice stopped, and that there are few, if any 'Radials', as suggested by some.

The under-table idea is a good one, and should be examined.
(Still not a fan of Glacial Erratics, though!)

Best wishes,
Neil

BRIAN JOHN said...

Yes, lots of plough marks to the W of Stonehenge. But elsewhere? I wish I knew what micro-morphology the LIDAR image is showing up.

We shouldn't use the term "ice striations" as that implies direct glacial erosion. I don't think that's what we are looking at here. Although I think the ice might well have reached Salisbury plain 450,000 years ago, I doubt that it had the strength to leave deep elongated gouges on the scale of these ridges and rilles. Too much speculation from all of us, I'm afraid -- has anybody ever made a proper map of these stripes or grooves, or whatever we want to call them? If so, can we see it please?

Constantinos Ragazas said...

Brian,

Wont the LIDAR images showing the Avenue stripes also have shown any other similar 'solutional rills' in the landscape? And if there are no other such solutional rills, wont that argue against your claim these Avenue stripes are such solutional rills? This being so regardless of whether or not the Avenue stripes “owe their orientations partly to some structural control in the chalk bedrock”.

Clearly, the process responsible for the formation of these 'solutional stripes' was also responsible for the straight diagonal orientation of these Avenue stripes AS WELL AS the nonexistence of other such features in the landscape.

After you have exhausted all improbable possibilities of how these Avenue stripes formed, perhaps then you (and others) may be ready to seriously consider my explanation of these.

Namely, the Avenue was a meltwater channel etched in an ice sheet cover and draining the retaining basin that Stonehenge once was!

Kostas

ND Wiseman said...

Hi Brian - thanks for the quick response.
While you are certainly the Go-To Guy when it comes to these things, I was always given to understand that the Glaciation of 23/4,000 years ago was responsible for the rills, ergo: Ice Striations.

My sense is that the LiDAR doesn't penetrate the ground, but uses a very precise method to measure surface contours - so we wouldn't see the stripes in any case, buried under a foot or so of topsoil.

Ground penetrating radar has been used, indeed was done extensively during the Riverside Project, ordered by none other than your Nemesis, MPP.
He was sort of following up on Atkinson's observations.

I have heard many speculate that they are mostly run-off of rain and ground water, but this doesn't explain how they're so straight for such a long stretch.
I'm sticking to the Ice Explanation until something better comes along.

Even if it Was 450,000 years ago the features would probably still survive in that stable chalk.

Repeated speculation has a way of becoming truth, and this is amply illustrated with many SH questions.

Best from this chair,
Neil

BRIAN JOHN said...

Neil -- we are looking at terminology here. The term "ice striations" means -- to a geomorphologist -- gouges or striations caused by over-riding ice. It is highly unlikely that that is how these features were formed, so we need to use different words. They may be Devensian in age (formed in the period 50,000 - 20,000 yrs BP) when periglacial conditions prevailed -- and indeed when permafrost might well have been present for many thousands of years.

I'm not sure how straight or continuous these rills are. Is that speculation, or is it backed up by field observations?

Constantinos Ragazas said...

Neil/Brian,

A 'thought experiment': Imagine two straight parallel cement walls running diagonally down slope from Stonehenge to River Avon. Imagine a stream of water flowing over the exposed chalk bedrock between these cement embankments. Imagine this stream existing for a long period of time.

Question: Would 'solutional rills' have formed similar to the Avenue stripes? A Yes or No answer would be sufficient.

Kostas

BRIAN JOHN said...

Kostas -- I fear that such a wondrous experiment would be just as spectacular a failure as the famous job creation scheme in Ireland round about the time of the Irish Famine, when somebody decided that a canal across a landscape of Carboniferous Limestone would be a great idea. When they let the water in, it promptly disappeared, leaving the canal high and dry. You might just have the same problem on chalk!

Constantinos Ragazas said...

Brian,

I am learning something new about you every day! Interesting!

So the water stream running down slope in my thought experiment would just disappear over chalk. But your rain/snow-melt run off would flow to create your 'solutional rills'!

I just think you are avoiding answering my question. Or unwilling to face the truth!

Kostas

BRIAN JOHN said...

Kostas -- you are not keeping up with the discussion. Look up "permafrost table" on Google.....

Constantinos Ragazas said...

Brian,

If you like to include some permafrost conditions in my 'thought experiment' feel free to do so. But please don't throw more chairs and other obstructions in the path of my argument. And please answer the question. Would stripes similar to the Avenue stripes be formed under conditions of my thought experiment?

Kostas

ND Wiseman said...

Hi Brian,
Yes - semantics seem to be playing a role here! lol
Actually, it is precisely the Devensian Ice to which I refer, so 'Periglacial' may well be appropriate.

The stripes tend to be fairly straight through their Avenue run thru SH Bottom (with the expected wiggles within this average), then slowly hook N/NE before disappearing from the studies. I believe (from memory) that this work was done in the 2006 season by the Riverside people.

I had overlooked permafrost, but now that you mention it, I wonder what role it may have played.
Would a lengthy deep-freeze cause the chalk underbed to perform as we see it at present?

If so, maybe we don't need an ice sheet at all?

More grist for the Mill,
Neil

BRIAN JOHN said...

Kostas. No.

BRIAN JOHN said...

Neil -- remember that during the Devensian we probably had 50,000 years of permafrost conditions during which periglacial conditions could operate on Salisbury Plain.

Second,I am not convinced that these stripes are continuous over great distances. From the photos I have seen we seem to have a pattern rather like that of a braided stream, with lots of interconnected rills weaving back and forth.

Third, yes, if permafrost was present at a depth of 2m (for example) in the summer season, that would act as an impermeable layer and allow water flow to occur in the soil layer, as we see in the Arctic today. This layer is then called the "active layer".

TonyH said...

Brian,

I commented on a previous Post on this same "periglacial stripes" topic, a while ago, that some of the archaeologists discussing this part of Salisbury Plain near Amesbury/ Durrington, had, also included in the collective authors, a geomorphologist from Southampton University. I suggested at the time he would be a good person to comment on our discussion and to get involved in our debate, as he is virtually on The Avenue's "doorstep", so to speak. His name came up in the last 2 years, I think. Stonehenge Riverside Project archaeologist,
Joshua Pollard, is also at Southampton Uni these days, and the Stonehenge Riverside Projects's Kate Welham is adjacent at Bournemouth University.
My own computer is currently out of action so I am checking the Blog in the public library when I can.

ND Wiseman said...

Hi again Brian,
Thanks for taking the time to discuss this with me. As you have no doubt accurately guessed, my Geology is woefully inadequate, and though I'm considered to be fairly bright in other areas, this one's obviously not my strong suit.
Therefore I only have logic to work with.

So then, as a 'fer instance' ...
A glacier comes along and scours the chalk. It sits there for a while just being ice before it begins to seasonally advance & retreat, yet leaves the permafrost beneath.
Local summer melt occurs and water flows along these channels, creating others. Eventually the ice goes away and we're left with all these rills and gouges.

Could the requisite compression & relaxation of the chalk also play a role in this process? (Not unlike squeezing and releasing a wet sponge?)

Your 'Braids' is a much better word than my 'Wiggles' - though in this case I was trying to convey the same idea.

Overall, the known courses are pretty straight, unlike many bona fide Ice Striations I have seen in the Canadian Arctic, where entire formations appear to wind left and right across the landscape over relatively short distances.

Best,
Neil

Constantinos Ragazas said...

Brian,

Yes, that was easy! But that will be hard to defend. Since nothing in my 'thought experiment' is different from what you argue formed these 'solutional rills'. Except for “some structural control in the chalk bedrock” and 'permafrost tables' confining these stripes diagonally down slope.

You argue for 'chalk bedrock' and 'permafrost tables' while I argue for 'ice embankments' controlling the water flow diagonally down slope. But, as Neil has pointed out, how does chalk bedrock and even permafrost tables account for these stripes running straight (more or less) confined to the Avenue for such long distance? My 'ice embankments' can! And how does your 'chalk bedrock and permafrost table' confine these stripes to the Avenue and nowhere else in the surrounding landscape? My 'ice embankments' explanation can!

I know you are annoyed. But in the spirit of reasoned honest debate I submit these thoughts to you and others interested in the truth.

Kostas

ND Wiseman said...

Hi all -
Just a bit of clarification here ...

It seems that our 'Rill & Gouge' discussion is veering into the similar vein of 'Assumptive Fact' which often labors other SH conversation.

The gouge-marks under the soil aren't just along the Avenue. They are throughout this entire local area, North, East & West.
The 90-foot wide Avenue merely glides along the most efficient run of these marks, due to the Henge's NE alignment Axis - but the Processional could easily have been placed anywhere within a reasonable distance to either side.

They do appear to cease mere yards before the Ditch & Bank and this has been my rationale for them to have placed Stonehenge more or less where it is.

Further, another factor with regard to this specific placement is that they very carefully incorporated the pre-existing, double-ringed North Barrow into the Henge Structure.
While the premise of its build will probably never be known, its special inclusion into the SH infrastructure suggests that it was originally placed there for many of the same reasons that the big, far more sophisticated Henge was, later on.

The 'Stripes' no doubt played an important role in that.

Best Wishes,
Neil

Constantinos Ragazas said...

Neil,

You write, “The gouge-marks under the soil aren't just along the Avenue. They are throughout this entire local area, North, East & West.”

I assume by the gouge-marks you mean the Avenue stripes. We all have seen pictures of these Avenue stripes from excavation reports done by MPP and others. We all know what these features look like. I myself wont characterize them as gouge-marks. But be that as it may.

What evidence is there of there being other such-like 'solutional stripes' in the chalk bedrock at the Stonehenge landscape? I have not seen any other similar pictures of such. And I have asked for such evidence often before. So you understand my keen interest in your claim there are such stripes in the chalk bedrock elsewhere at Stonehenge. Can you provide us with such evidence? Photos of these would be great!

Welcome to our debate!

Kostas

ND Wiseman said...

Hi Kostas,
(I was actually the one who commented on this thread first, so welcome to the debate - though I also realize that Brian & yourself have 'locked horns' in the past)

I am trying to access the Geophys Imaging Report locked somewhere in my Archives. This will be forthcoming.

I also have (what I assume everyone else has) the aerials by both Hamish Fenton and the other Kite Guy whose name escapes me at the moment, taken during the excavation by MPP. These illustrate the Rills very clearly, but the dig didn't exceed the boundaries of the Avenue.

Otherwise, the daring among us might wade into the maddening morass of the online EH Archive and review the Geophys from either 2006 or -07 for those reports.

Neil

BRIAN JOHN said...

Thanks Neil -- some more evidence would be very welcome here. If you can give URLs to any key info available on the web, I'll check it out and provide it for consideration on another post.

ND Wiseman said...

Hi Brian,
I've been sifting and scratching here to supply the evidence, then I look at your latest page-post and see that you've actually provided it yourself, after a fashion.

Over a very long time, ice was everywhere and there's rills, gouges and authentic Periglacial Striations all over the place.

The area around Stonehenge is no different.

The whole point of this conversation really is that the only curious quality of the stripes in that area is that they coincidentally align with the Solstice.

Without those stripes, this is a stupid, boring location far more effectively serving a Neolithic Community with farm land.
With the stripes we can all share a 'Eureka Moment' and understand why these environs were considered Sacred for arguably as long ago as 10,000 years.

Best,
Neil

BRIAN JOHN said...

Neil -- I have another post to come. Re the coincidence of the stripes just coinciding with the summer solstice sunrise, and providing the raison d'etre for Stonehenge being built here rather than anywhere else, I'm afraid I don't buy that. For a start, the subsurface rills and gullies were probably no more visible 5,000 years ago than they are today -- so it;'s far from certain that our Neolithic ancestors would have known about these "stripes" anyway. Secondly, that would be a pretty feeble reason for such a big building project. I still think that the stone monument was built here (rather than on the site of any other henge or circular earthwork) simply because there were a lot of very convenient stones lying about.....

TonyH said...

Hi Neil, Brian, Kostas et al,

Mike |Parker Pearson has certainly exploited (no cynicism intended) the SRP's "discovery" of the peri - glacial stripes [or whatever we should call them with the assistance of Brian, the glaciologist/ geomorphologist]. He has emblazoned the back cover of his "Stonehenge", 2012, with a description of how these stripes were 'found' by his SRP team, and that he concludes that Neolithic folk there may have regarded the Stonehenge site as an "ompholos", or centre of the world/ universe.

Cheers
Tony

geocur said...

The reason for choosing the site was clearly not because of the availability of stone . Why wait 500 years before taking advantage of the reason for choosing the site .

Constantinos Ragazas said...

Neil et al,

As Brian shows in his latest post (“Chalk Surface Grooves Everywhere”) and you have also argued, grooves/'solutional rills' can and do exist anywhere on the chalk surface.

But what we have here with the Avenue Stripes are natural 'solutional rills' that defy gravity! Running more or less diagonally straight between the Avenue Banks for some 500 m. And then mysteriously disappearing at the “elbow” along with the Avenue.

MPP may like to claim this natural feature to explain the erection of Stonehenge. But MPP cannot explain how these Avenue Stripes naturally formed with these features.

What seems evident to me is the water flow responsible for these 'solutional rills' had to be structurally controlled on the SURFACE of the chalk. And be so controlled diagonally for a stretch straight for some 500 m.

Brian's subterranean bedding explanation just does not explain this.

Kostas

Constantinos Ragazas said...

Brian,

If you understand Geo's last comment please explain it to me!

Kostas

Myris of Alexandria said...

There is only one true ompholos. That of Sublime Apollo in Delphi.
Very very very sad news of Iain M. Banks.
His last novel is called The Quarry.
I know that GCU.In two minds is mindful of the cosmic irony.
M

BRIAN JOHN said...

Geo -- what is clear to you is not clear to me. They started using stone when it suited them, or when some wacky individual with gigantic aspirations came along.....

geocur said...

Brian , I said that it was clearly not the reason for choosing the site . Why defer the reason for that choice for 500 years .

BRIAN JOHN said...

Depends whose chronology you believe, Geo. As I understand it, MPP et al now think that the stones were used right from the beginning -- and that the ditch and bank were built at about the same time as stones were put into the Aubrey holes. Whose chronology are you faithful to?

geocur said...

Brian, I'm more concerned with the evidence .34 of the 56 Aubrey holes have been excavated , none had evidence of bluestones fragments in their base ,similarly none found in the earliest phase of the nearby ditch . Hawley initially believed they had held stones as some had crushing at the side ,possibly consistent with the removal of a stone or post, then changed his mind . Basically there is no evidence for them ever having held bluestones .

ND Wiseman said...

Hi Gang …
We are straying perilously close to the discussion which I had hoped to avoid. That is: The Glacial Erratic case for Stone Erection.
I will qualify my following remarks by saying that I have enormous respect for Brian, his work, and for him as a person, but I do not subscribe to the notion.

OK ― that said, let me dance around the subject on one foot with a hand tied behind my back …

On discovering the Stripes.
During Mesolithic Times the Stonehenge Landscape was lightly forested. As the people settled in, they used the trees for the usual stuff, clearing the woods for farming and whatnot. The so-called ‘Car-Park Totems’ may well be from these woods.
Now let’s cut down all the trees for firewood and see what happens. Well, it rains and snows all over this disturbed, shallow topsoil for a while. On the slope to the Bottom, I have a feeling that the now-loose ground was partially slewed down the hill and revealed these curious, previously unseen contours.

No matter if they were caused by Ice, Water or the Finger of God, they are there, and they follow the Solstice Axis.

These folks, like just about everyone else up to and including the present day, were Sun Worshippers. So this must have been pretty big news, and is why, in a nutshell, the otherwise boring place was eventually considered the Center of the Universe.
The two Cursus’s are older than Stonehenge as is Robin Hood’s Ball. Vaspasian’s Camp is older. The Totems are older. Coneybury is almost certainly older. All kinds of local Ritual Builds are older. This was a Sacred Landscape.
My feeling is that they were compelled to build Stonehenge here ― not because there was a bunch of Bluestones conveniently lying about, but because this was clearly the place where Father Sun met his beautiful Earth Wife in June.

OK ― now… When they dug the Ditch for Stonehenge it is unlikely that they could envision the Sarsen Build of 350-odd years later. There probably were Bluestones. Whether these were inserted into all 56 Aubreys or just a few ― or even rotated between them periodically is not known, essentially because they haven’t all been excavated as yet. But Something was in these Holes from the earliest times.

Where did all these interesting rocks come from?
Well, we now know that most of the several varieties came from Wales.
How did they get there?
Maybe Ice brought them part of the way ― maybe not. Humans were certainly involved in at least the final stages.

We look at some great Gothic Cathedral, or the Empire State Building, or the Eiffel Tower…
Our initial, overwhelming impression is: How Grand!
Only later do we ask: How’d they do that? Or: Where’d those rocks or steel come from?
The wonder of Stonehenge does not come from its quarries or how the Stone was collected and delivered. It comes from the concerted effort of over 40 generations to construct an edifice, which on several levels, was the ultimate Neolithic Statement Monument.

I’m not sure what the roundhouse discussion is really about anymore. There are rills in the Avenue. They fortuitously point towards the Solstice. Guess how cool that discovery must have been?
Ultimately, who cares how the rocks got there.

Best,
Neil

TonyH said...

Geo and all

"The reason for choosing the [Stonehenge] site was clearly not the availability of stone".

But there may well have been far more sarsen stones (apart from BJ's case for there having been a glacial deposition of assorted "bluestones"). Colin Gibson was set the task of checking the O.S. maps by MPP & found plenty of evidence in the late 19th Century therein). See MPP'S latest book, index Bulford Stone.

TonyH said...

Re the recent debate between Brian & Geo about choosing the Stonehenge site because of the availability of stone (or not), it is worth looking at MPP's 2012 book where he mentions his Professorial colleague, Colin Gibson, going off to check the Victorian large - scale Ordnance Survey maps for the whereabout of substantial boulders, etc, and finding plenty. I think you'll find this via tne book's index by looking up " The Bulford Stone". MPP goes on to speculate that largish stones may have re-located around the wider Stonehenge landscape during prehistoric times, rather as seems to have occurred within the Inner Circle.

Myris of Alexandria. said...

The Aubrey Holes do have bluestone 'debitage' found within them. Many of them.
Are the weasel words 'in their base'?
That I do not know as I am unsure where in the Aubrey Holes the fragments occurred.
The original excavation reports should state that.
M
Aubrey Hole 7 even has a bit of SH48 knock-off (now who is being semantically correct).

Jon Morris said...

Basically there is no evidence for them ever having held bluestones .

Apart from MPP's inspection of the chalk layer?

To get a compacted surface at the interface usually requires a significant weight above ground and through the surface layer: The above ground segment increases the effective bearing pressure considerably.

but it's difficult to comment: None of us have seen it.

BRIAN JOHN said...

Neil -- I fear that I have no sympathy at all for the thesis that the rills or stripes (or whatever you want to call them) that coincided with the sunrise on the midsummer solstice were so SPECIAL that the phenomenon led to the construction of Stonehenge. Some rills run this way, and some run that way. Some hill summits are aligned with this, and others with that. Some slopes face north and some slopes face south. No big deal, I am afraid, no matter how sacred the landscape may have been..

ND Wiseman said...

Hi Gang (again)
The following sentence of my previous post:
[i]The two Cursus’s are older than Stonehenge, as is Robin Hood’s Ball. Vaspasian’s Camp is older. The Totems are older. Coneybury is almost certainly older.[/i}

should have had added to it:

[i]... but none of these constructs included Stone. If they were lying around all over the place, why not use them from the very earliest moment?[/i]

Best,
Neil

geocur said...

Myris ,"in their base " is all important not "weasel words " .AH 7 had more than Bluestone debtage it also had a cremation ,pottery an axe fragment and sarsen flakes and mauls .Not only stratigraphically but contextually suggestive of the sarsen and bluestone erection phase ,not the earlier evidence free bluestone erection phase recently suggested to coincide with the bank and ditch construction .

BRIAN JOHN said...

I don't understand this argument about stones being used at the earliest opportunity if they happened to be lying around. Why use stones if nobody is particularly inclined to use them? Or if there is no cultural "fashion" involving the creation of megaliths? Big stones weren't used for making monuments in the Palaeolithic or Mesolithic either, as far as we are aware. Copper ore wasn't used until the time was right, either. Neither was iron ore until smelting techniques were sufficiently well developed. Neither was the wheel used, in spite of there being plenty of trees around. One could go on......

geocur said...

Tony , yes sarsen was likely to be around but I believe Brian was thinking along the lines of glacially transported bluestones .Whether they were there or not I don't believe the reason for choosing the site was due their presence .

geocur said...

Jon , Hawley had noted the compaction much earlier .It could have been due to the presence of posts as nearly everyone until very recently believed . There is no evidence for the Aubrey Holes having held bluestones .

BRIAN JOHN said...

Geo -- I have always argued that the "stone assemblage" was a mixture of abundant sarsens AND erratics from far away. We don't know that when the stones were first used there was a differentiation between sarsens and bluestones. I suspect there may have been an early grouping of stones according to size. It's quite possible that some of the sarsen lintels, for example, were used earlier as free-standing orthostats -- maybe even in the Aubrey Holes??!!

BRIAN JOHN said...

We are getting a bit off topic here, folks.......

geocur said...

Brain , you suggested that the reason for choosing the site was due to their presence ." I still think that the stone monument was built here (rather than on the site of any other henge or circular earthwork) simply because there were a lot of very convenient stones lying about....."
Why choose that spot because of the handy stones then not use them for half a millenium .Foresight ? "Someday or childrens ,childrens ,children (and son on for 20 generations ) will thank us for saving them the trouble ?

BRIAN JOHN said...

Geo -- see my earlier answer. Nothing to add...

Jon Morris said...

Jon , Hawley had noted the compaction much earlier .It could have been due to the presence of posts as nearly everyone until very recently believed . There is no evidence for the Aubrey Holes having held bluestones .

Brian's right: A bit off topic, but worth a final comment as this is also one of the tags I have in MPP's book (and Brian's input on this would be very welcome)

It's true that timber posts could compact the base of a hole. However the effective ground bearing pressure of a timber post say 2 metres high is in the order of one whole magnitude less than an equivalent bluestone (timber is much lighter than soil): The reason this is important is that the increase in overload with timber is only some 50-60% whereas the increase with an equivalent bluestone, it is in the region of 500%

50% might result in very light compaction. Timber posts can cause heavy compaction during the construction phase, but the signs of this should be noticeable to an expert.

500%, an effective pressure of some 70kPa or so, is significantly less than chalk's bearing capacity. Nevertheless, it should be sufficient to result in heavy compaction combined with local remoulding.

In engineering, there are devices we use (I have several variants of this for different materials in the office) that can assess compaction. The type of remoulding and compaction should be easy for an expert to assess. Though none of us have actually seen it, local remoulding would be the tell-tale and I thought it was reasonable to rely on MPP's judgement?

GCU.intwominds said...

Weasel words, as here, are often the most significant.
Mike Pitts was the main AH 7 excavator.
Perhaps we should wait to see what the monograph says.
Myris.
Off topic is often more fun and instructive.

geocur said...

Brian , it doesn't matter what the assemblage of stone may have consisted of . It doesn't seem a likely reason for choosing the site then not making use of that reason for 500 years .The use of sarsen in the Aubrey Holes has been discounted because of the size of the holes .

geocur said...

Jon , until recently MPP and others involved in the Riverside project like others before them concluded that the impaction was due to posts . If you read his judgement from the book it is “If we were right that they (Aubrey Holes ) once held bluestones … “ hardly assured , this is later rationalised to “Aubrey Holes with bluestones in them . I suspect that a driving force behind the thinking is that wooden posts in the Aubrey Holes is anathema to the Durrington / Stonehenge binary opposition .

BRIAN JOHN said...

Geo -- I find your reasoning very convoluted. Henges and earthworks were built all over the place. Mostly they were not developed into something different. Here, at Stonehenge, they also built a stone monument within the earthwork. Why? Because there were lots of stones lying about, and somebody had the brilliant idea of using them. Your argument that they would have used the stones right from the earliest stage of work on the site just does not make sense. As I have said, history is full of resources being available but unused -- until a technology became available for using them, or unless there was a sudden cultural imperative to mimic something done elsewhere, or to initiate and do something quite exceptional. Do you have a problem with that?

BRIAN JOHN said...

Geo -- you say: "The use of sarsen in the Aubrey Holes has been discounted because of the size of the holes." By whom? And which sarsens are they talking about?

geocur said...

In the case of AH 7 , primary fill and secondary fill might be the weasel words but we know from Hawley's earlier and surely , main excavation , the significance of the bluestone and sarsen finds and they didn't suggets the AH had ever held a bluestone or for that matter a sarsen , can the monograph deny that ? Mike Pitts re-excavated AH 7 .

geocur said...

Brian , I find your thinking convoluted .
The builders of Stonehenge created a bank and ditched monument with the addition of burial deposits , the reason for choosing the site is very unlikely to have been based on the availability of stone as they didn't use any in the earliest phase of the monument . .When the megalithic monument began at Stonehenge is was almost certainly due to the presence of the earlier monument .The building of megalithic monuments on the site of earlier sites like enclosed cremation cemeteries , sites with depositions or timber monuments is common . Many stone circles are merely one of a series of monument types built at a site which had earlier consisted of timber monuments , burial deposits or even mesolithic middens .Most major megalithic sites have a history of development over time evolving from one type of monument to another . Not only is the stone availability idea unlikely there is no evidence for bluestones having been at the site prior to the earliest monument .

BRIAN JOHN said...

Geo -- this is getting absurd. I didn't say that they built the bank and ditch at Stonehenge because there were stones in the area. We don't know why they built the bank and ditch here -- neither do we know why they built banks and ditches elsewhere in some locations rather than in some other locations. All I am saying is that the STONE monument was probably built here because there were plenty of stones around -- and because a particular group of people had the bright idea of doing something interesting with them.

geocur said...

Brian,
More importantly , who has claimed the AH pits held sarsens ?
I can't think of anyone .
MPP has noted that there is no evidence of any sarsen dressing /fragments from the primary fills or ditch and it seems unlikely that undressed sarsens would fit into the relatively homogeneous sized pits .

geocur said...

Brian ,what I have been saying is that the stone monument was built at the site because of the presence of the earlier monument , not because of available stone . Sarsen may have been ubiquitous in the area and they could have chosen anywhere to build the megalithic monument ,they chose the site they did as in so many other similar cases because of the pre-existing monument .

GCU.intwominds said...

Yes you are correct. Mike Pitts reexcavated AH7.
I forget that not everyone follows the circus so closely as we.
Myris

BRIAN JOHN said...

Geo -- you say: "it seems unlikely that undressed sarsens would fit into the relatively homogeneous sized pits." Since when were all sarsens too big? Do you suppose that they are all the same size? Sarsens come in all shapes and sizes, like bluestones. Some of them might have fitted into the holes, and some might not.

I don't care whether anybody else has ever suggested that some of the holes might have held small sarsens -- maybe some that were later used as lintels. If nobody has ever suggested it before, remember that you saw it here first.....

Constantinos Ragazas said...

Geo et al,

When in a conundrum, try questioning your assumptions.

What exactly dates the Ditch as built before the megalith erections? Deer antlers buried in the ditch?

Kostas

geocur said...

Brian ,as I mentioned I was quoting MPP . The dressed lintels are 1m wide . The undressed stone would presumably be wider . There are two Aubrey Holes with a diameter of of just over 1.6m and one at 1.8 the others are either below a metre or slightly over a metre . Hawley who excavated and saw the compaction in more Aubrey holes than anyone , and was later to change his mind about the presence of any type of stone in the AH 's , noted that “they once held small upright stones “ not even a suggestion of a bluestone never mind a lintel .And as noted earlier there is no evidence of any fragments of sarsen or bluestone from the primary fill of the holes .

geocur said...

For those of us who never use “ common sense “ “question our assumptions “ or bother with “ the truth “ but do read the literature ,some of the the reason that the ditch is believed to date before the the megalithic erections are 1) The ditch has no bluestone or sarsen fragments in it's primary fill . 2) Antler picks (11) found at ditch bottom produce a combined date of 3000 -2920 BC whilst antler picks (7)from packing around sarsen circle , sarsen trilithons and bluestone circle , produced dates of 2640-2485 BC ,2480-2340 BC etc .
3)The centre point of the AH circle and ditch and bank are almost identical and could not have been laid with any certainty if there were obstructions in the centre of the monument 4) A Pig tibia from the secondary fill dated 2450-2150 BC provides a terminus post quem for the secondary infilling of the ditch .
5) No bluestone or sarsen fragments in primary filling or secondary filling the first find of any bluestone fragments is when the ditch is filled to near the top of it's cut .

David Norcott said...

Hello gents - if you have any queries about the geoarchaeology of the area I'd be happy to help.

These features (often referred to by as periglacial stripes) are pretty much ubiquitous on the chalk where there hasn't been sufficient subsequent erosion to remove them. They are technically 'patterned ground', a phenomena caused by the sorting of material by frost-heaving. A link to a useful wiki page here: http://en.wikipedia.org/wiki/Patterned_ground.

They generally run more-or-less downslope, and are often discontinuous. When the slope is very shallow or flat, 'blobby' shapes can be produced instead of stripes - these features show much better on gravels, where well-defined linear features can be created on the slopes, and neat polygons on the flats. These are not features caused by flowing water.

I hope this is useful.

Regards

David Norcott
Senior Geoarchaeologist
Wessex Archaeology

BRIAN JOHN said...

Hi David

Welcome! Good to have your comments. You may not have seen the many other posts on this topic -- type in "periglacial stripes" into the search box, and you will probably find 20 or more posts! As I have explained in a number of posts, I am not entirely convinced by the patterned ground thesis, especially where the stripes do not run directly downslope, but are diagonal -- as Charly French suggests.

If these stripes are ubiquitous, presumably you have
no time at all for the MPP thesis that it was the orientation of 2 stripes that led to Stonehenge being built where it is?

Have you seen polygons on Salisbury Plain? If so, info please!

David Norcott said...

Hi Brian
I haven't searched through the posts (am pressed for time at the moment), but it would be fair to say that I don't consider the stripes to have any bearing at all on any of the archaeology present - they are everywhere, and don't always run directly downslope.
Neat polygons don't form on chalk, you tend to get blobby irregular shapes instead. These are usually interpreted as tree-throws or solution hollows by field archaeologists.
Regards
Dave

David Norcott said...

As a follow-up, from what I remember of the programme (which in places I had to watch through my fingers), I had the impression that MPP was saying that there were pre-existing geological mounds or ridges beneath the avenue banks, in addition to the stripes. These raised areas were of course the result of the underlying chalk being protected from rainwater dissolution and ploughing, and were there because of the banks, not vice-versa.
Regards
Dave