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

Monday, 23 January 2012

On Glacial Cycles


This looks a bit daunting (from Patton et al, 2011) but it's really not that difficult.  It shows the main glacial cycles -- known from work all over the world -- over the past million years or so.  The interglacial phases (highlighted by nice yellow sunshine) are labelled I 1-11 and the glacials (marked with blue ice!) are numbered G 1-10.

The Devensian Glaciation is the most recent glacial episode, lasting from c 73,000 years ago to 14,000 years ago.  The Anglian Glaciation -- which I have assumed to be the one responsible for the transport of the Stonehenge bluestones -- was around 450,000 years ago.  But notice that there are several other big glaciations -- and we have very little idea what effects these episodes might have had in western Britain (in Eastern Britain things are a bit clearer).  Phases G2 and G7 were particularly large glaciations, and the ice of the Irish Sea Glacier might well have been almost as extensive in those phases as it was during the Anglian.

One of the great implications of this pattern is that any erratics that we might find in the landscape have probably had multiple trips and zig-zag courses....

Source:
Modelling the dynamic instabilities of palaeo ice-sheets
Henry Patton, Alun Hubbard, Neil Glasser ,Tom Bradwell, Nicholas Golledge
IGES Presentation 2011

30 comments:

chris johnson said...

Thanks Brian for another wonderful post. I am having trouble keeping pace.

I think the rocks in question (I deliberately avoid the word Bluestone) are some 450 million years old. Correct?

So they could have been moved to the Stonehenge area by glaciers on many occasions.

In my short acquaintance with this subject I am thinking that glaciation is by far the most likely transportation theory - at least for the longer distance. I am now puzzling how the stones were shaped. Could it be that they arrived at some period in a meltwater river valley and were smoothed somewhat by natural forces?

You make the point several times that these stone are not particular sympathetic to working by hand and liable to fracture. It seems then that doing the final shaping by hand at Stonehenge would have been a particularly frustrating endeavor.

All the more wondrous that they are standing now where they are.

BRIAN JOHN said...

Chris -- yes, the bluestones are for the most part from the Ordovician -- as you say, around 450 million years old. And yes, they could have been moved in any one of several glacial episodes in the Quaternary. the elongated shape of some of the bluestones is a difficult problem -- I have discussed this earlier. Long thin stones are very liable to fracture, however they are transported! I don't think there is any evidence for transport in a meltwater valley -- but we know that some of the stones were worked by hand, probably at Stonehenge -- cf the mortise and tenon and tongue and groove features......

My instinct at present is that the stone (or stones) that came from Craig Rhosyfelin was a big rough lump that was more of a nuisance than anything else, so it was simply broken up to get rid of it. Hence all that debitage....

There is no evidence that it was elongated or of any use at all as an orthostat or standing stone. That is all pure speculation.

Anonymous said...

Brian,

“My instinct at present is that the stone (or stones) that came from Craig Rhosyfelin was a big rough lump that was more of a nuisance than anything else, so it was simply broken up to get rid of it. Hence all that debitage....”


Really???

Why not move the broken nuisance lumps by rolling them down the hill?

chris johnson said...

Interesting. Perhaps you are right about the Rhos-y-felin stones and they were indeed broken up over the centuries in-situ to prepare pork chops or whatever. But the main puzzle remains: the "bluestones" set as jewels in the two rings. These are substantial orthostats and well shaped.

When we accept that they too were transported by glaciers it raises the interest puzzle of where they were divided into the "polished" orthostats we see today and how it might have been done.

Had it been a giant erratic (my favorite), how might it have been possible to divide such a stone into many roughly equal parts? So many questions, sorry for that. One day I might have some answers.

BRIAN JOHN said...

Anon -- lumps of rhyolite suitable for rolling down the hill? What a nice idea -- maybe you should go and look for them in Stonehenge Bottom.

BRIAN JOHN said...

Chris -- the idea of a single super-erratic doesn't hold up because there are so many different rock types in the bluestone assemblage. My own preference if for a mottley collection of stones, of all sorts of shapes and sizes some of which were elongated enough to be used as orthostats, and others which were more like slabs or boulders. Some of the elongated ones were worked on the site (or maybe nearby?) for use in stone settings which changed frequnrly. the most inconvenient boulders were just broken up -- maybe some were used for making implements? Some others were put into stone settings and later removed or broken up -- the bluestone stumps may represent some of them.

BRIAN JOHN said...

oops -- frequently....

chris johnson said...

It will be interesting to see when the road is broken up exactly how many stones have found their way into the hard core over the centuries.

BRIAN JOHN said...

Yes Chris -- or (as Rob has argued) how much hard core from the roadworks over the years has found its way into the soil and maybe even into the Stonehenge Layer, thereby causing great confusion.......

Geo Cur said...

“My instinct at present is that the stone (or stones) that came from Craig Rhosyfelin was a big rough lump that was more of a nuisance than anything else, so it was simply broken up to get rid of it. Hence all that debitage....”
Ignoring the inconvenient fact that there is no evidence for glaciation from Preseli to Salisbury Plain this suggestion is up there with the best of the post processualists at their most playful. The poor quality stuff manages to get transported to the site in a big lump , whilst the good stuff is in convenient blocks . I’m not quite sure if the suggestion is that the big block was actually the centrepiece of the monument/ debitage , in which case it would have been an obvious explanation for choosing the site in the first place or maybe it was just outside the area and brought into the centre of what was to become the debitage , either way it dawned on the punters that it had been a bad decision (either accepting this as the special spot or bringing this useless lump into the monument ) it became clear that it was a kind of GA/TD healing stone in reverse and now needed smashing up , couldn’t be simpler ,you can’t help wonder where the instinct came in .

BRIAN JOHN said...

Hang onto your hat, Geo -- just doing a bit of innocent speculating. I'm not THAT bothered, one way or another.

So what's YOUR explanation for all the foliated rhyolite debitage which does not match any of the known standing stones at Stonehenge? Come on now -- how about a bit of speculating to keep us entertained?

Geo Cur said...

Mere speculation . Destruction of what were orthostats starting in the Bell Beaker period and continuing until at least the medieval period .

BRIAN JOHN said...

Fair enough. Time will tell...

Confused said...

Brian,
Part 1
"My instinct at present is that the stone (or stones) that came from Craig Rhosyfelin was a big rough lump that was more of a nuisance than anything else, so it was simply broken up to get rid of it. Hence all that debitage...".

I've been trying to figure out what would be the nuisance value of a large lump of rock in Neolithic times, and I have had no success.
It would not have blocked a road for they could simply have treated it as a roundabout, (traffic-circle for our American bloggers); and there were no airports, factories or power stations to worry about; nevertheless, it would have provided a fine wind-break for animals and their owners, or even a place to make speeches from; but causing a nuisance I fail to see.

What do you see as its nuisance value, please?

Part 2.
"So what's YOUR explanation for all the foliated rhyolite debitage which does not match any of the known standing stones at Stonehenge? Come on now -- how about a bit of speculating to keep us entertained?"

In Ixer and Bevins 2011 - Craig Rhos-y-felin, Pont Saeson Is The Dominant Source Of The Stonehenge Rhyolitic 'Debitage', states that previous macroscopical examination of the debitage from the April 2008 excavation (and subsequent examinations of material from The Stonehenge Great Cursus, the Heel Stone area, the Stonehenge Avenue and from a number of Aubrey Holes)originally divided the rhyolitic rocks into thirty descriptive groups, which were subsequently simplified into three major and two very minor classes(RAI unpublished data) namely;

A. Dark/black, sharp,flinty rhyolite +/- joint planes. Rare, pale-coloured, flinty rhyolite is probably weathered dark rhyolite.

B. -----

C. -----

D. -----

If class 'A' above is flinty rhyolite then would this perhaps indicate it being imported for tool making purposes?

Confused again, naturally.

BRIAN JOHN said...

Nuisance value -- inconvenient rocks would have a great nuisance value if they were simply in the way of whatever was going on. If the builders of Stonehenge found an assemblage of stones in a small area and decided they would do something interesting with them, they would use the best stones in stone settings,and break up those that were not of much use. The essence of this bit of speculation is that the SITE of Stonehenge was determined simply by the availability of stone in some abundance. (I have suggested before that the Altar Stone, for example, may still be where they found it, and was used as a sort of focal point for the stone settings.....)

Was the flinty rhyolite imported? Well, Rob Ixer and Richard Bevins wisely stay clear of speculation on that, and simply make the point that the rhyolite debitage that they have been able to look at (and that is clearly not all of it) appears to have come from fewer sources rather than the many which they one assumed. As I have said before, a nice bit of geology -- not much help when it comes to the archaeology.

Confused again said...

Brian,
To reiterate the quote ---
"My instinct at present is that the stone (or stones) that came from Craig Rhosyfelin was a big rough lump that was more of a nuisance than anything else, so it was simply broken up to get rid of it. Hence all that debitage....".

Plus quote 2
"Nuisance value -- inconvenient rocks would have a great nuisance value if they were simply in the way of whatever was going on."

Quote 1 implies that the big lump of rock ended up at either the Cursus site, the Heel Stone site, the Avenue site or in the area of the Aubrey Holes; that is, the areas from which the debitage was collected..

Quote 2 suggests that the big lump was interfering with construction at the above mentioned sites which implies that humans or glaciation had to transport the rock, but as has been pointed out before, we have evidence of human activity in the area but we are still waiting evidence to show that glaciation occurred at these places.

Quote 3
"(I have suggested before that the Altar Stone, for example, may still be where they found it, and was used as a sort of focal point for the stone settings.....)".

Would it not have been easier to have used the big rock as the centre-piece rather than the Altar Stone, unless of course the Altar Stone had some spiritual significance?

Still Confused

BRIAN JOHN said...

Actually we are probably all confused...... I have no idea how big the rock or rocks which provided the rhyolite debitage might have been. The only way to work that out would be to calculate weights and volumes of rhyolite fragments, but we clearly do not have enough data for that to be done. The occurrence of foliated rhyolites at the Cursus and elsewhere is intriguing to say the least -- and Ixer and Bevins have not sought to explain that. Neither has anybody else. Any suggestions? As a confused person, your suggestion is just as likely to be sensible as anybody else's...

One of the great imponderables in all of this is sampling bias. We do not know how widespread these foliated rhyolite fragments really are, and whether there are large areas where these particular fragments do NOT exist.

chris johnson said...

I suppose it is always safe in academia to flee towards more detail when you don't have a theory.

I would like to know what Brian's theory is. A "straw man" that can be shot at.

So were these miscellaneous stones picked up by a Welsh Icecap and dropped on an Irish Sea stream and transported conveniently to Stonehenge. If so, how, and is this convincing to other geologists or geomorphologists - it seems not?

Please Brian put an integrated theory forward. As a layman I can accept that glaciers can quarry and move stones, but this is very general. Simulations of the welsh ice raise more questions in my mind than they answer.

Why is it that several groups of stones were dropped conveniently in a similar place by possibly several different glaciations? Meantime the same glaciations seem to have left no indicators of their path?

On the one hand we are asked to believe that it is totally logical that Lampeter-Velfrey stones can be dropped where they are, while there is a missing link - no stones - on the way to Stonehenge.

Brian, please, tell me how you think it happened. Much more data and I will be back to believing in human transport.

BRIAN JOHN said...

God, I don't know if I can cope with all this pressure! An integrated theory to explain absolutely everything?

A few points. First, I have never suggested that several glaciations terminated in the same general area, around Stonehenge. That would be too much of a coincidence..... What I have suggested is that some of the erratics in the assemblage might have been picked up and dumped several times, thus following a zig-zag or erratic course. That would be perfectly normal. (For example, the Altar Stone must have been transported initially by Welsh ice coming down from the uplands before being incorporated into an Irish Sea Glacier ice stream. Maybe some of the eastern Preseli erratics have also been moved at some stage by Welsh Ice -- we have no way of knowing, at present.)

Second, there is nothing strange about the dolerite erratics at Lampeter Velfrey, as I have tried to explain to Geo. Strahan and the other old geologists found erratics all over the place in South Pembrokeshire -- and the directions of transport were broadly consistent.

Third, we do know a lot about ice movement directions up the Bristol Channel. I didn't invent the maps! Many other geologists and geomorphologists have done that, over the years, using the evidence of striae, till characteristics and erratic transport routes. Look at this post:
http://brian-mountainman.blogspot.com/2011/09/erratics-and-deposits-in-vale-of.html

Remember that if you want to hunt for a trail of erratics you will have to do it out in the middle of the Bristol Channel and the Severn Estuary. Not that you will necessarily expect a continuous trail anyway -- as I have explained, erratics are often transported and dumped in clusters.

My theory is in the book, Chris! I have not come across anything -- in spite of very intense scrutiny on this blog -- to dent my confidence in its essential reliability.

Geo Cur said...

Brian , I never suggested that there was anything strange about erratics being found at Lampeter Valfrey , it was the fact that they were chemically identical to orthostats from Stonehenge and rarely mentioned was what I found noteworthy

Toatally confused said...

Brian,
Another quote ----- "(For example, the Altar Stone must have been transported initially by Welsh ice coming down from the uplands before being incorporated into an Irish Sea Glacier ice stream. ---"

What if the Altar Stone was transported eastwards from the Brecon area by humans, crossing the River Severn above Gloucester and on to Stonehenge?

The answer to the secret of the universe and everything else is 47.

Anonymous said...

Dear Brian,

It is now apparent you will not post any more of my contributions responding to relevant points you and others raise. I held on to hope and a false belief for an 'honest debate'. I am fed up with you and your censorship of my voice in a dishonest debate.

I will no longer contribute to your blog, after being one of your most loyal and consistent contributors for over two years. But I will continue to read your blog and monitor the evidence and direction of the arguments.

The field is now wide open for more myth-making. “Architect tombs” or “stone destruction”? Sound the same to me! You have lost your battle with the archeologists! But don't expect them to embrace you in their ranks!

A “heroic failure”? More like a character flaw and self-contradiction! Sorry it turned out this way!

Good luck!

Constantinos Ragazas

BRIAN JOHN said...

Well there are those who say that, including Prof MPP. I couldn't possibly comment.

Yes, the answer to everything is indeed 47. But there are only 43 bluestones at Stonehenge. Maybe there were 47 originally?

BRIAN JOHN said...

Farewell, Kostas! Your loyalty has been a mixed blessing. I'm sorry if I have a flawed character -- but I assure you that I strive for perfection.

I make no apologies for blocking many of your posts -- I hope you will set up your own blog and have a jolly time in the future discussing things with whichever readers may choose to follow it.....

As for whether I have lost my battle with the archaeologists, time will tell. I don't see it as a battle anyway -- we have a sharing of ideas, which will eventually lead to a convergence of evidence and some sort of consensus. That is the way with science.

chris johnson said...

Dear Brian,
the answer to everything is 42. Not sure where 47 comes from.

Goodbye kostas, it was fun knowing you!

chris johnson said...

Geo_cur, first I heard of Lampeter Velfrey is when you brought it up. First I thought of the real Lampeter which is where many of my family originate and which is in a completely different direction. Strange indeed it might have been!!

Now I know that Lampeter Velfrey is a different place, near Narbeth, and very plausible for transportation from the Welsh icecap - never mind Irish Sea streams. It might even be construed to be on the ice road to Stonehenge.

The close vicinity has been quarried for stone for a long period so one might easily imagine that any convenient stone was taken along. The Church was also present in a significant way and so pagan memorials might have suffered - there are vague rumors of a stone circle on the village green but no extant traces. Additionally Lampeter Velfrey was on a cart road for a couple of hundred years, so likely any handy stones would have been consumed for hardcore.

All in all I doubt Lampeter Velfrey is worth a visit, and any erratics still standing in the hedgerows can be logically understood. Chemical links between such stones and Prescelly and Stonehenge are easily explained.

Perhaps we can safely forget about Lampeter Velfrey, although it does lie in a beautiful location?

Geo Cur said...

Chris , I'm sure Lampeter Valfrey would be worth a visit .
Anything I have commented about the place and the erratics has been been perfectly clear i.e. the erratics known about since the early 20th C are now known to be be chemically identical to Carnmnenyn and Stonehenge orthostats , this I find interesting and also the fact that it has generally been ignored , no more no less .

Slightly Confused said...

Brian,
Take no notice of Chris, he's got it all wrong. The answer to everything is definitely 47 because that's the number of the house where I was born, whereas those living in 42 were clearly disturbed.

p.s. I'm not so confused since I've taken some tablets, tablets, tablets ---- who mentioned tablets?

BRIAN JOHN said...

As I have pointed out, the erratics were collected from the fields -- just some of them appear to come from the Carn Meini area, but others are from unknown sources.

Geo Cur said...

As I have pointed out the erratics I was talking about were the dolerites and not the others . see 16 /12 /2011 "erratic mysteries "
"They describe the erratics as being a varied assemblage ...spotted dolerite ,rhyolite (?) lavas and pyrocalstic rocks . A chemical study of the dolerites showed that the major and trace element compositions were identical to Preseli dolerites of the Carnmenyn/Carngyfrwy area ."