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Monday, 10 October 2011

On elongated erratics

The gallery of glacial erratics pasted in above illustrates the fact that for the most part erratics are referred to as "boulders" since their length:width:depth ratios are not far removed from 1:1:1.  Sometimes the length of the boulder can be twice that of the width, but there are not many cases in the literature where the proportions go up to 3:1:1.  In other words, pillars or columns are rare.  The reason is that during glacial transport, even if a pillar is entrained by the ice,  the stresses placed upon it are so huge that breakage is almost inevitable -- except in rare cases where the debris falls onto the glacier and is transported along on or near the ice surface.  James Scourse goes so far as to argue that pillars the shape of the bluestone pillars at Stonehenge can not possibly have been transported by ice all the way from Pembrokeshire to Stonehenge without being broken down into chunks or boulders.  That is a reasonable argument, and I can see where James is coming from.

However, look at the photos in a bit more detail, and you can see that some erratics are fissured or bedded to such an extent that it is surprising that they have not been broken up into much smaller flattish slabs during entrainment, transport and dumping.  Look at the bedding in the third erratic from the top -- part of the Big Rocks erratic train in North America.  And the bottom two photos -- one from western Ireland and the other from Lofoten, in Norway, show that elongated erratics can be transported and dumped without being broken into small pieces.  Are those occurrences freaky or unusual?  Yes, to some degree they are -- but even if only 5% of erratics of this shape survive, at least we have a reminder that we should never use the word "impossible" in our discussions.

NOW HERE'S MY LATEST BIG IDEA.

What if a number of "giant erratics" were entrained by the Irish Sea Glacier as it crossed Pembrokeshire and were carried to Salisbury Plain during the Anglian Glaciation?  By "giant erratics" I mean room-sized erratics -- or even larger, weighing hundreds or even thousands of tonnes.  The Big Rocks erratic group at Okotoks is the classic example -- but there are plenty of others, some of which I have posted up before on this blog.  Look at these:


Notice that thebottom two erratics are fractured, foliated or bedded -- again it is surprising that they have travelled on or in ice without being broken up.  Maybe they were even bigger to start with.......

So here's my big idea -- several rather big slabs of rock were picked up by overriding ice in Pembrokeshire (for example from the Craig Rhosyfelin area, from Carn Goedog and maybe Carn Meini) and dumped at or near Stonehenge in a cluster.  The Neolithic builders of Stonehenge built the monument there because they had an easy source of raw materials conveniently to hand.  So they "quarried" their slabs and pillars there, on the spot -- not in the "bluestone quarries" in Pembrokeshire that have so obsessed the learned professors.  There might also have been other isolated erratics in the same general area, which were collected up and incorporated into the stone settings.  If there was a lot of stone working on the site, that might go some way to explaining the vast quantity of "debitage" and the abundant fragments in the Stonehenge layer -- and we might also explain the apparent use of rhyolite and "preselite" for the making of stone tools.  (Maybe these stone tools did not come from the destruction of bluestone orthostats, but from the waste materials left behind after the extraction of the "pillars" from the giant erratics.)  Many people have of course speculated about the "Stonehenge axe factory."

Just thinking out loud here -- but until somebody puts me off it, I think this is rather a nice theory........

10 comments:

Constantinos Ragazas said...

Brian you write,

“...during glacial transport, even if a pillar is entrained by the ice,  the stresses placed upon it are so huge that breakage is almost inevitable -- except in rare cases where the debris falls onto the glacier and is transported along on or near the ice surface.”


Yet another reason why my 'ice cover theory' is likely correct! Since from what you and others argue, the only way the Stonehenge stones could have been brought to Stonehenge by ice is on an ice surface and not in a glacier mass.

As for your 'big idea' of glaciers bringing the whole quarry to Stonehenge rather than the stones … makes 'human transport' sensible in comparison!

Kostas

BRIAN JOHN said...

Kostas -- you forgot to mention my "however" bit. The fact of the matter is that very rarely elongated or pillar-shaped erratics DO get entrained and transported. the circumstances are exceptional, admittedly, but the point I was making is that we should not use the word "impossible" in this context.

Bringing the whole quarry to Stonehenge? I know it sounds mad, but just think of the Big Rocks erratic group -- and here is another quore re erratics in Iowa:

"......geologist Charles Gwynne of Iowa State University described the fate of a large Black Hawk County erratic near Waterloo. It originally measured 30 feet long, by 20 feet wide, by 27 feet high and was broken up in 1891; the pieces were used to construct the Boulder Church which housed the congregation of the First Presbyterian Church in Waterloo. This building was used as late as 1961 by the Salvation Army. The 1916 Annual Report of the Iowa Geological Survey described a boulder in Floyd County, about three miles west of Nashua, as the largest erratic remaining in Iowa. Its dimensions then were 50 feet long by 40 feet wide by 11.5 feet above the ground, with a nearby fragment measuring 17 feet by 7 feet by 1.5 feet apparently broken from the larger rock. In 1961, this same erratic was listed as being 40 feet by 30 feet by 12 feet. Other large erratics that can still be seen are St. Peter's Rock four miles southeast of Alta Vista in Chickasaw County, a granite specimen five miles west of Cedar Falls in Grundy County, and a granite boulder in Grammer Grove Park in Marshall County."

I don't want to get into a catalogue of "giant erratics" -- but take it from me that there are plenty of them, sheared off the glacier bed by overriding ice.

Geo Cur said...

Sometimes they get marked .I found this one about 5 years ago .
http://www.themodernantiquarian.com/site/8456/gleann_da_eig.html

Constantinos Ragazas said...

Brian,

I am not questioning the existence of monstrous erratics carried by glaciers. The pictures speak well for themselves. But imagining prehistoric men cutting pillar stones out of these using stone axes just seems a little (a lot) improbable to me. If they had such capabilities and intent, why wont they quarry the stones in a more regular shape? Why work on the stones while errect rather than when quarried? Why leave such imperfections in a monument significant to their lives and believes?

Also, monstrous erratics carried such long distances would of course become very rounded and so very unsuitable for quarrying 'pillar stones' using stone axes! And what happened to what remained unused? Wont such be found nearby Stonehenge? And if one monstrous erratic was brought to Salisbury from Preseli, wont you expect maybe another one or two or three to be carried and deposited also?

One possibility could be that while entrained and carried by glacier mass, the monstrous erratics broke up along natural seams to create the kind of pillar stones we see at Preseli and at Stonehenge!

The explanation becomes more complicated, if the explanation is not the right one. Truth, like love, lights the way!

Kostas

G. Peterson said...

As a non-academic visitor to this site, it would be appreciated if Dr. John, or anyone else, could explain in simple terms, why the bluestones could not have been transported from the Preseli area to Stonehenge, by people?

Many thanks,

George Peterson

BRIAN JOHN said...

George -- many things are possible, including glacial transport of the stones, human transport of the stones, and a combination of the one and the other. What is PROBABLE is another matter. I have argued consistently that the theory of the human transport of the stones is inherently improbable, because the bluestones have come from so many sources, in difficult terrain, and because all the other evidence we have from this country indicates that Neolithic megalith builders always used whatever building materials were readily to hand. We have no evidence to support the human transport theory, in spite of what the archaeologists may tell you -- all they have is speculation.

Secondly, using the principle of Occam's Razor, we do not actually need a highly complex and imaginative theory if we have a simple one that will do. The human transport theory is not needed. The glacial transport theory has a good deal of evidence to support it, as we have discussed on many occasions on this blog. It is perfectly "fit for purpose" -- and that's good enough for me.

George said...

Brian,
Thanks for the guidance.

Two other things that you may be able to help with.

I understand that, at some time, you took part in transporting the Millenium Stone.
The photos I've seen show a small army of people pulling it, along a roadway on a sled.

Could you please tell me how many people had to be used to move the stone, and did it travel over other types of surface?

Constantinos Ragazas said...

George,

I appreciate your earnest question. Let me give you my earnest answer.

In order for the bluestones to have been transported by prehistoric people over 250 km distance through rugged land and sea, advanced technical knowledge and skills would have been necessary.

The people had to be well organized with social and economic development and a belief system in order to bring the masses to a single-minded purpose that had no practical utility.

Such cultural development would have left ample other evidence of it existing. Like written records, public buildings, carved symbols, images and names of gods or rulers, and evidence of commerce. And all this some 1000 years BEFORE the earliest known civilizations. No such records exist! No mention of such people exist by people existing at the time.

Furthermore, scientific estimates of the population size of the UK at the time Stonehenge is said to have been built is just a few tens of thousands of people. If you consider that only a fraction of the population could have been able to participate in such physically difficult tasks (excluding children and the sick and old people and women, etc.) and the short life span of prehistoric people, it just does not seem possible or reasonable for prehistoric people to had the resources or intent to engage in such improbable tasks. That would have taken them away from the daily struggle for survival in very harsh and difficult living conditions.

Many people believe Stonehenge was built by people since 'how else' could it have been built, they argue. In my article, “The un-Henging of Stonehenge” (google the title) and in this blog I argue that Nature may had a greater role in the construction of Stonehenge. With prehistoric people contributing commensurate with their known capabilities.

Nothing is settled about Stonehenge! But arriving at the truth will require an open mind free of dogma and idolatry.

Kostas

BRIAN JOHN said...

George -- the full history of the Millennium Stone pull is in my book called "The Bluestone Enigma" -- and if you put in "Millennium Stone" into the search box on this blog, you will find much more. I won't repeat all of that again -- except to say that the whole exercise was a shambles that demonstrated to all of us that the human transport of 82 stones from here to there would have been attended by so many huge problems as to have made it virtually impossible. (I won't say "totally impossible" -- that would perhaps be going too far!)

George Peterson said...

Brian and Kostas,
My thanks to you both, I shall ponder on your replies.

George