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Friday, 13 February 2015

Understanding the Bluestone Circle



  
Stones 34 (above) and 37 (below) of the Bluestone Circle at Stonehenge.  Both stones are made of spotted dolerite.  The one above is best described as a rounded boulder set on end, and the lower stone is best described as an irregular slab; we are looking at the flattest face in the photo.  No self-respecting Neolithic orthostat collector would give these stones a second glance, let alone go all the way to West Wales to collect them.  They are heavily worn glacial erratics, carried a long way by ice and probably collected from the Stonehenge landscape by the builders of the monument. 
(Photos from the Stones of Stonehenge web site.)

Work in progress.........

There are nineteen visible stones in the Bluestone Circle and also assorted buried stumps.  Here is an attempt at itemising the full list, with reference to stone shapes, surface characteristics and petrology:

31 -- damaged and heavily worn slab.  Standing.  Recent damage close to ground level.  Spotted dolerite with few spots.
32 -- heavily worn slightly elongated boulder.  Fallen -- resting on stone 150.  Spotted dolerite with pinkish spots -- like stones 150, 34, 35A, 35B (one stone), 39 (?), 47, 49, 64, 67, 69, 70
32c -- altered volcanic ash.  Like 33d.  Foliated rhyolite related to Rhosyfelin debitage?
32d -- another foliated rhyolite stump?  Related to Rhosyfelin material?
32e -- Dolerite stump -- characteristics unknown
33 -- well worn short and stumpy pillar.  Standing.  Signs of shaping -- meant as a lintel?  Spotted dolerite with whitish spots.
33e -- altered volcanic ash (stump).  Like 32c
33f -- altered volcanic ash (stump).  Laminated -- like 40c and 41d
34 -- well rounded small boulder, placed on end.  Spotted dolerite with pinkish spots -- like 32?
35 a and 35 b -- irregular and well worn boulder, embedded in the ground and only just visible.  Spotted dolerite with pinkish spots -- like 32?
36 -- an irregular and heavily worn boulder, slightly elongated.  Modern damage on one edge.  Recumbent
37 -- smallish well-rounded boulder, slightly slab-shaped and set on end.  Spotted dolerite with moderate spots.
38 --  smallish irregular boulder, well worn, fallen and under another stone.  Rhyolite, ignimbrite. Dacitic ash-flow tuff.
39 -- another smallish boulder, well worn, slightly slab-shaped, with some later damage.  Leaning, almost recumbent.  Spotted dolerite with pinkish spots -- like 32?
40 -- Rhyolite, ignimbrite. Dacitic ash-flow tuff. Stump beneath ground? Laminated --  like 33f and 41d?
40c -- stump. Laminated calcareous ash
40g -- below ground stump -- irregular shape. Micaceous andstone. Lower Palaeozoic?
41 --  recumbent elongated boulder with heavy wear -- very well rounded edges
41d -- stump.  Altered volcanic ash.  Laminated -- like 33f and 40c
42 -- recumbent wedge-shaped stone with heavy wear on edges.  Densely spotted dolerite?
42c -- stump.  Sandstone (micaceous).  Lower Palaeozoic?
43 -- recumbent slightly flattened boulder with heavy wear on edges.  Densely spotted dolerite?
44 -- heavily worn boulder just visible in the turf -- recumbent.  Spotted dolerite?  Similar to Boles Barrow dolerite?
45 -- recumbent elongated boulder with heavy wear on edges.  Unspotted dolerite? Different from 44.
46 -- slightly slab-shaped boulder set on edge.  Flaky -- considerable recent surface damage.  Rhyolitic ash-flow tuff like stone 48? Or is it a lava?
47 -- slab with heavy wear on edges -- set on end.  Spotted dolerite with pinkish spots -- like 32?
48 -- small recumbent boulder with heavy wear --  just projecting through the turf.  Rhyolitic ash-flow tuff (flinty blue) but not like stone 46?
49 -- small irregular slab with quite sharp edges.  Upright.  Signs of dressing? Intended as a lintel?  Spotted dolerite with pinkish spots -- like 32?

Note that there are at least a dozen dolerites in this collection -- so not all of the available dolerites were placed into the Bluestone Horseshoe.  The dolerite slabs and boulders of assorted shapes and sizes were used in the Bluestone Circle, and the more elongated dolerites (the pillars) were used in the Horseshoe.  So it can NOT be argued that the builders of Stonehenge were intent on collecting dolerite PILLARS from Preseli to the exclusion of all other dolerite shapes.  Here they have used a weird assortment of dolerites of all shapes and sizes.  As suggested in earlier posts, the presence of slabs, roughly rectangular blocks and boulders -- for the most part with rounded-off edges and corners and with an overall shape we will refer to as "sub-rounded" -- is highly suggestive of long-distance glacier transport.  It is logical to assume that these stones (we won't call them "orthostats") are not simply glacial erratics but glacial erratics that have travelled a long way.  In other words, they have in all probability been collected from Salisbury Plain or somewhere near it.

The OU team (which involved Olwen Williams-Thorpe and Rob Ixer) had consent from EH to sample 11 of the dolerite orthostats in the Bluestone Horseshoe and 4 of the "rhyolite" orthostats in the Bluestone Circle.  that means that cores were taken.  Were there any measurements and analyses of the weathering crusts revealed in these cores?

17 comments:

Constantinos Ragazas said...

Brian,

You write, "No self-respecting Neolithic orthostat collector would give these stones a second glance, let alone go all the way to West Wales to collect them. "

What self-respecting Neolithic orthostat builder would have given these stones a second glance, let alone go all out to erect them?

There lies the inherent self-contradiction with your reasoning here, Brian.

Kostas

BRIAN JOHN said...

No contradiction, Kostas. It's all to do with costs and benefits. An orthostat BUILDER (part of your friendly neighbourhood business community) might well use little stumpy stones if he was building a stone circle for you and your budget was tight. he would use whatever was at hand. There are stone settings like this all over the UK and the rest of Europe -- so insignificant in terms of overall landscape impact that you often miss them. In Pembrokeshire there are several (like Gors Fawr and Bedd Arthur) where hardy any of the stones project more than a metre above the ground surface. If, on the other hand, you were working to a much larger budget and were sent off to Wales to find magnificent pillars -- in order to make some grand architectural statement at Stonehenge -- why would you bother with small boulders, slabs and blocks if you found them lying about on the ground? And yet, here they are at Stonehenge. They used them because they were available (at very modest cost!) from Bert's Rock Depot in Amesbury and because there was nothing else to be had at the time. There was a big demand for rocks at the time, and those people over at Avebury had grabbed most of the interesting ones......

Constantinos Ragazas said...

Brian,

Playing the devil's advocate here, why can't it be argued the bluestones at Stonehenge once looked like the Rhosyfelin "proto-orthostat" and the rounding and shaping of these was intentional? And not due to glacial transport?

We may not like it or understand it, but the Neolithic ancestors did!

Kostas

Constantinos Ragazas said...

Brian,

Playing the devil's advocate here, why can't it be argued the bluestones at Stonehenge once looked like the Rhosyfelin "proto-orthostat" and the rounding and shaping of these was intentional? And not due to glacial transport?

We may not like it or understand it, but the Neolithic ancestors did!

Kostas

Alex Gee said...

Brian
Probably one of the best points you've made.

Why the rates of erosion of rocks of an identical lithology, should
prove to be higher on Salisbury Plain, than in mountainous terrain, is a very good question!

Given the vast body of geological research into denudation, it could well cause the proponents of quarrying serious difficulties!

Congratulations for bringing quantative measurement into the debate!

BRIAN JOHN said...

Alex -- the interesting thing is that the degree of rounding and scale of abrasion on the stones in the bluestone circle seem to be higher overall than the degree of rounding and abrasion on megalithic structures in Pembrokeshire. Let's assume that almost all of the stones used in megalithic structures in Wales are glacial erratics used more or less where they were found. They seem to me to be moderately abraded -- ie not transported very far. That does indeed seem to be the case when you look at the lithologies involved -- they are mostly rather local. In contrast, the bluestone circle stones look really FAR-TRAVELLED, with heavily abraded edges and corners.

None of this is very quantitative -- I'd like to do some proper quantification to see if this stands up......

The only other thing that might have influenced the rounding on the bluestone circle stones is VERY LONG EXPOSURE and HEAVY WEATHERING -- as we see on many of the boulders in the granite areas of Brittany, for example, where there has (so far as we know) been no Pleistocene glaciation. Hundreds of thousands of years exposed to the elements can cause the rounding off of edges and corners.....

More on this to come....

TonyH said...

Strikes me that the bluestones erected in the Stonehenge circle, found SOMEWHERE sufficiently close to the future Stonehenge having been deposited as erratics by an obliging glacier, were regarded as "Gifts From The Gods" by the Salisbury Plain and Beyond Prehistoric Folk. Now, you can put EITHER a very prosaic interpretation on what are "Gifts From The Gods": that they were merely conveniently located stones. OR, you may be more poetically or romantically inclined, and think that it was their unusual appearance, the exotic "otherness" of the stones' appearance, setting them apart from any they had encountered elsewhere in the future Wessex, that led to humans deciding to incorporate them into the prehistoric temple.

BRIAN JOHN said...

Nicely put, Tony. I think I would go along with that.

Constantinos Ragazas said...

Imagine, Tony, if the same bluestones were brought to Salisbury Plain by Walsh quarrymen! These "gifts from the gods" than would have gods bringing them there! And mobilized the people to build Stonehenge to worship them!

MPP is thrilled I am sure at such suggestions!

Kostas

BRIAN JOHN said...

Kostas -- this is no doubt what the archaeologists will say -- namely that the shape,size and appearance of the stones is quite immaterial, and that the bearers of stones were simply carrying them to Stonehenge because they were magic, and because they contained the spirits of the ancestors. So a stone picked up in Crymych, for example, carried with it the soul of Grandpa Dafydd who lived there long ago. This is more or less what MPP has said in some of his lectures..........

On the other hand Profs D and W would probably say these strange stones were carried because they were found adjacent to certain sacred springs in eastern Preseli, and were therefore also invested with magical or healing powers. In other words, they were transported not because they had HISTORICAL significance, but because they had MEDICAL significance.

Wonderful fantasies which you can never either prove or disprove -- such is the way with modern archaeology, where the story is everything.

Constantinos Ragazas said...

Brian

I agree with all that! So why add more fuel to the architypal fire? We must stick to facts and not fantasy, if the light of truth can ever shine on us!

Kostas

TonyH said...

Kostas, the "Gifts From The Gods" I described were delivered to Wessex courtesy of Geomorphological/ Glaciological processes. These are Global Wonders enough for me, without the need to summon up magical fantasies of Inter - Tribal Co - operation and Treking from Proto - West Wales to Proto - Wessex. I am singing from the BJ Hymnbook, as you well know. I thought you and I, as fellow - Seekers after Truth, were agreed upon that!

peter Style said...

To cut to the quick, whist I concur, from a layman's point of view, that many of the Stonehenge bluestones - on the face of it at least - appear to have the characteristics consistent with glacial erosion; how about devoting a blog post to the remaining bluestone erratics found in the Wessex region that were not collected by the builders of Stonehenge. That would surely produce a more convincing narrative.

Constantinos Ragazas said...

Tony,

We are agreed on that. I was playing devil's advocate to give Brian more opportunity to elaborate and make his case stronger.

I do question, however, any motivation we ascribe to Neolithic people for Stonehenge. That's what archies do. That's what we must not do! Nor need to do!

Kostas

BRIAN JOHN said...

Peter -- at various times I have tried to do that on this blog, listing "strange stones" which can, to all intents and purposes, be called bluestones since they are not sarsens. There are lots af anomalous stone fragments and other occurrences in the literature, but getting photos of them and analysing their characteristics is not easy.....

BRIAN JOHN said...

I made a start here in 2011 -- and there are assorted other mentions on "strange stones" on the blog too.

http://brian-mountainman.blogspot.com.es/2011/11/stray-stones-in-south-west-england.html

There is no doubt that the strange erratics on the coast near Croyde and Saunton share the same shape characteristics as the bluestones in the bluestone circle. A lot of wear and much rounding off of edges and corners.

TonyH said...

A while back I recall you had a series of Posts on "bluestones" photographed and described by accomplished photographer Pete Glastonbury in villages e.g. north of Salisbury Plain e.g. Edington. We speculated on how these stones had ended up in prominent roadside positions. I am sure Peter Style could find these Posts via this Blog's Search facility by putting in one or two keywords e.g Peter Glastonbury.