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Saturday, 24 November 2012

Rhosyfelin -- is it a quarry site?




Below I have posted a short note written by Phil Morgan, in which he considers the question of whether Rhosyfelin really does have a man-made quarry there, or whether everything is natural...... I happen to disagree with many of the things that Phil says, but discussion is always good!

1.  I quite accept that where quarrying is contemplated, it makes more sense to take stones from sloping walls where things will slide down under some degree of control, rather than from overhangs where there is great danger.  So from that point of view the rock face at Rhosyfelin which looks down on the dig site is "suitable." This wall faces NW, as Phil says.

2.  I don't agree that there would have been less freeze-thaw activity under a periglacial climate regime on the NW face than on the SE face.  I think there may well have been more on that side, since with westerly winds predominating in this area, the SE face would have been relatively more protected by lee-side accumulations of snow, which inhibit freeze-thaw processes and frost shattering.

3.  Orientation of big blocks.  Phil mentions that there are 4 blocks lying at right-angles to the rock face -- I don't see that.  If you look at all my photos on this site, and at the Gigapan, what you see is a jumble of fallen and broken blocks and scree with no preferred orientations.  So I don't agree that this tells us anything at all about human involvement.  I agree it would be interesting to know how many of the blocks have fallen directly down from the higher parts of the rock face, and how much downslope movement there may have been -- ie movement broadly parallel with the rock face. A factor which Phil doesn't consider at all is the influence of ice and snow-banks in all of this -- scree slopes in high-latitude or periglacial environments are very complex indeed, with snow, ice and running water all playing roles and with rocks falling down onto ice or snow and then sliding or settling later on.  Believe me -- I have crawled about on such slopes many times in my wild youth!

4.  The large block and the rails.  Again, I don't agree with Phil.  It could perfectly well have fallen and slid on ice or snow into its present position.  No human agency needed -- and there are no rails either, as I have pointed out.  Has anybody suggested that the longish stones beneath the big "orthostat" are made of mudstone?  They look like perfectly ordinary local rhyolite to me.....

5.  Heather as an indicator of quarrying activity?  Sorry Phil, but there is heather all over the place in areas which have not been quarried. I don't believe a word of what you say here.

In short, I see nothing here or anywhere else to shift me from the view that this jumble of rocks, large and small, is entirely natural.



Rhosyfelin -- is it a quarry site?



Figure 1 – Stope


1). Quarry workers are concerned over where rocks fall, nature cares not.

Gold mining practice utilises ‘Stopes’, where large caverns are excavated to access the gold bearing veins. The ore veins seldom exist at a convenient angle for extraction, resulting in the sides of the stope forming steep angles with the ground, (Figure 1)

When mining operations form these steep angles the sides of the workings are named the ‘foot’ wall and the ‘hanging’ wall. The safer rock face to work is the foot wall side for the product slides down-slope to the floor, whereas when working the hanging wall there is always the danger of the side collapsing and falling vertically, which could cause injury.

The Neolithic stone gatherers would have disliked being struck by falling stones and they would have realised that working the Craig Rhos-Y-Felin outcrop from the ‘foot’ wall side, (north-west face), would be the safer option.


Figure 2 (below) – Craig Rhos-Y-Felin ‘Foot-wall’.






Figure 3 (below) – Craig Rhos-Y-Felin ‘hanging Wall’.






2). Considering the actions of ‘freeze-thaw’

The photo only shows the dig in the area of the north-west face of the outcrop, the face that would have been least exposed to the actions of freeze-thaw; whereas the ‘hanging’ wall, (south-east face), which would have been more susceptible does not appear to have the same smooth finish of the foot wall.

It may prove beneficial to place a small trench below the south-east face to examine any debris for similar large blocks of rock. If no such blocks are found then it would again support human activity.

3). Orientations of the larger stone blocks.

Gravity is unable to differentiate between human quarrying and natural quarrying; it is logical to think that the quarried material comes to rest in the same manner for both activities, and that the orientations would not favour either quarrying method.

However, it is unusual that there are four blocks lying at right angles to the rock face. I suggest that a search be made to see if the upper surface of each block correlates with the rock face immediately above it. If it does then it is more likely that it was wrenched from the solid with it rotating about its base as it fell, indicates human activity, (figure 4).





If the underside of each block correlates with the solid rock then it is more likely to have become detached by natural means and slid down the rock face, (Figure 5).

It is normal, and best, practice when removing rock from the solid, to work to a free face, which in this case would be to work from the top of the outcrop vertically downwards. Therefore, the above correlation test should initially be applied to the upper portions of the outcrop.

The method used to separate the blocks is unknown but the use of water to expand wooden wedges inserted in the natural joints of the rock would work, especially if combined with the use of levers and ropes.

4). The large block lying parallel to the rock face.

It is thought that this slab is too far from the rock face to have come to rest after falling by human or natural means. Therefore, it is reasonable to say that it has been moved.

Mention has been made of this stone resting on ‘rails’, however this could be purely by accident. It is suggested that the ‘rails’ be examined to verify whether they are made of the same rhyolite as the igneous outcrop, or of some foreign stone, particularly mudstone.

Mudstone becomes slippery when wet, especially when under load. The pressure breaks down the rock surface which forms a lubricating interface.

Craig Rhos-Y-Felin is situated in the Fishguard Volcanic Group of rocks, however, the mudstones of the Aber Mawr Formations are reasonably close and southwards, upstream of the Afon Brynberian.

If the rails are formed from mudstone this would again support the human activity principle.

5). Heather as an indicator of human quarrying activity.

A study has been made of the use of heather as an indicator that quarrying has been conducted by humans. Craig Rhos-Y-Felin formed a part of this study and proved to be an ideal candidate for human quarrying.

Briefly the study has shown that heather, which has an affinity for acidic soils, flourishes on man-made, acidic, scree slopes, while refusing to grow on identical, and adjacent, natural scree.

It seems the reason for this abnormal activity is that, generally, natural scree slopes have been formed by freeze-thaw during past ice ages, when no plant life could survive. However, all human quarrying activity has to have taken place after the last Ice Age when plant life could survive.

The heather at Craig Rhos-Y-Felin grows only on the igneous outcrop, (figure 6).

Figure 6 – Heather and gorse growth at Craig Rhos-Y-Felin.







It is thought that the combination of orientations of the four rock slabs, the changed direction of the fifth slab, the use of ‘rails’ possibly made of imported mudstone combined with the presence of heather indicates that this area has been quarried by human hand.

Phil Morgan, Inc. Eng.
18th September 2012

61 comments:

Anonymous said...

Brian,

Is Phil's argument for 'human quarrying' at Rhosyfelin the sum total of all the evidence for 'human quarrying' at Rhosyfelin? What evidence does MPP use? There was no mention for the faint vertical parallel lines marking the “orthostat” at Rhosyfelin.

Phil's “cartoon reasoning” in your post is ludicrous. A little like using a painting of the resurrection of Christ as evidence for the resurrection of Christ!

Kostas

BRIAN JOHN said...

Well, there are rumours of hammerstones -- but the evidence (if it is evidence) is being kept under wraps........

Anonymous said...

Brian,

Shouldn't the evidence for “human quarrying” at Rhosyfelin precede the verdict? And isn't this 'backward causation' akin to tainting the jury pool before the trial even begins?

Kostas

BRIAN JOHN said...

Of course you are quite right, Kostas. My impression is that MPP and his colleagues had decided this was a bluestone quarry connected to Stonehenge even before they had looked at it. That's why I was so appalled by the presentation given in Newport last year after the 2011 dig -- I still think of that as one of the worst (ie most unscientific) presentations I have ever heard.

Dave Maynard said...

Figure 2 looks interesting. I'd say that the north face is 'modified'. Was this taken before the excavation?

BRIAN JOHN said...

On what basis do you say that, Dave? Doesn't look modified to me...... I suspect the photo was taken after clearance of the bushes along the face, and before the commencement of excavations. But maybe Phil will confirm?

chris johnson said...

I did see and hold two hammerstones at Bryberian and MPP explained to me plausibly why he is confident they were used as hammerstones. A bit more than a rumour.

BRIAN JOHN said...

What was MPP's reasoning here? Were there clear percussion fractures and damage that might indicate that these are USED pebbles or cobbles rather than just rounded stones found in their natural positions?

Jon Morris said...

Were any ultrasound tests considered Dave? A more recent surface might have a lack of mid-depth rebound caused by deep cracking.

Myris of Alexandria said...

Kostas
Phil is a highly experienced, respected/regarded mining engineer so his kindness in explaining to non-mining laymen what should be expected is of value.
Whilst St Thomas should ever be our patron saint and guide, nothing that Phil has written is ludicrous (pace the heather - that is an herb too far for me).
He suggestions as to determining what is the 'top and bottom of the quasi-proto-orthostats are germane.
M

chris johnson said...

Brian,
These hammerstones had damage that might reasonably be assumed to have been caused by impact with other hard objects. When and why is a legitimate subject for speculation, but that they are the result of deliberate and repeated human action seems most likely. I cannot imagine that the damage resulted from any natural process.

So we have round boulders of 20-30kg (estimated) which are easy to hold on the smooth side and with fractures on the bottom side. Seems to me that they were used to smash into something hard and fractured as a result. Given the weight and my strength, this hammering was not subtle.

@ Myris. Could not have said it better myself!

BRIAN JOHN said...

It would be good to examine those stones -- if they are 20-30 kg in weight they would be quite heavy for bashing things with. If the evidence id strong that some stone working went on here, I have no problem with that. If we really do have a hearth of some sort, and a pit that might have held a standing stone at some stage, people must have been doing things here. The question is this -- were they "doing things" for strictly local purposes (utilitarian or "ritual") -- or were they working in a quarry from which large quantities of stone were transported all the way ton Stonehenge? Although MPP and his colleagues seem to be accepting the latter option, that seems to me to be an act of faith rather than anything based on hard facts.

Anonymous said...

Myris my friend,

I can always count on you (and Brian) to point out my bad manners! My apologies to Phil.

My 'ludicrous' comment concerned the “cartoon reasoning” used to persuade (not prove) the non-mindful layman. Since other scenarios can be just as likely, showing something opposite to his conviction. His “cartoon reasoning” (for me) was nothing more than testimony of his faith. Thus the analogy!

Kostas

Anonymous said...

Brian,

There may be many explanations for these hammerstones. Let me offer another possibility to contemplate.

Could these be rounded stones found along rushing stream banks that also polished the smooth face of the outcrop at Rhosyfelin? Than latter pummeled by falling spree from the outcrop face?

Kostas

chris johnson said...

Brian, they are heavy. I was immediately reminded of the lesson of using hammers - let the weight of the head and gravity do the work.

The theory at Rhosyfelin from MPP and the team seemed to be that the stones were erected locally and subsequently moved to Stonehenge - so no direct link with the "quarry".

@Kostas. Stones in the streams look quite different - nice try.

Jon Morris said...

Apologies for getting Phil and Dave's names mixed up. Some interesting ideas brought up by the thread.

BRIAN JOHN said...

Chris -- stones in streams (even very well rounded ones) do break up at times, and they do also get percussion marks on them if they are struck by rolling boulders at times of flood. They can also shear off fragments or slices if there are inherent weaknesses in the stone or pebble. This is not a simple matter.....

TonyH said...

The place to see hammerstones in profusion is Salisbury Museum, close to the Cathedral, but used in the building of Stonehenge. These are on display for all to see. We could do with the World Specialist Expert producing a Paper, with photographs for comparison purposes, of the hammerstones of Stonehenge and those claimed for Rhosyfelin. Then a geomorphologist could also be invited to look at both sets of hammerstones, from Wales and England, and he could submit his own report based upon HIS specialist knowledge. There is obviously little doubt about the useage of the hammerstones found at Britain's premier megalithic monument. Presumably, they could be, or have been, examined meticulously and this could be taken further, just as the laser examinations of the Stonehenge orthostats have revealed amazing new detailings.

Phil morgan said...

Hello all,
The First Part,

1). Thanks to Myris and Chris for your support,the cheques are in the post :-).
The heather project is ongoing, I may yet convince Myris of its value.

2). Dave, the photo labelled Figure 2 was taken on the 9th January 2012; between the first and second excavations.

3). Jon, no need to apologise, I easily confuse myself.
Perhaps Myris knows of any ultrasound scans being carried out.

4). Clarification is required for some of Brians comments.

The short note was a response to the following request from a member of the Rhos-Y-Felin excavation team:

"Dear Phil
This is the 'quarry' site
What do you make of the orientations of ALL the blocks. Would all or any fall that way naturally??
This is a very hush hush photo but I want the opinion of a mining engineer/massive rock person

cheers."

The request was received prior to any photos being being made public, consequently, my observations were made on the basis of the single photo provided.

Brian, in his response has, understandably, used a photo from his own collection, for neither of us has permission to use the photo supplied in the request.
Brian states:

"Orientation of big blocks.

Phil mentions that there are 4 blocks lying at right-angles to the rock face -- I don't see that. If you look at all my photos on this site, and at the Gigapan, what you see is a jumble of fallen and broken blocks and scree with no preferred orientations. So I don't agree that this tells us anything at all about human involvement."

The current photo provided by Brian for illustration, shows the view from the south-west, whereas the photo provided for my opinion, showed the view from the north-east.
The photo I received, i.e. from the north-east, clearly shows four blocks lying at right angles to the face.
A close approximation to the image sent to me, was taken by Brian and posted on this blog on the 19th September 2012.
It is a photo of the whole 2012 dig, and it clearly shows the four slabs resting at right angles to the rock face; together with the single 'rotated' large slab.

Phil Morgan,

Part two to follow


Phil M. said...

The Second Part.

Regarding 'Freeze-Thaw'
The publication:

'CRAIG RHOS-Y-FELIN, PONT SAESON IS THE DOMINANT SOURCE OF THE STONEHENGE RHYOLITIC ‘DEBITAGE’
Rob Ixer1 and Richard Bevins2'

provides a satellite image of the sampling sites labelled as follows:

'Figure 1. Aerial photograph of Pont Saeson and the prominent northeast-southwest oriented Craig Rhos-y-felin showing the
2010 collecting sites (Localities 1 – 12).Grid squares are 20m x 20m. Locality 8 is at the extreme northeastern end of the
crag.'

I agree that when the site in question,i.e. locality 8, was covered in snow, it would have been insulated from the actions of frost.
However, when the snow, which inhibits freeze-thaw processes and frost shattering, retreats, the location, which is due north, would not have experienced warming by the Sun during the day, and then rapid cooling at night. This would reduce the chances of the rock shattering and the effects of 'freeze-thaw'.
Is this not the same as warming with fire, and then cooling with water, a recognised method of breaking rock in ancient times.

Brian also says:
"A factor which Phil doesn't consider at all is the influence of ice and snow-banks in all of this -- scree slopes in high-latitude or periglacial environments are very complex indeed, with snow, ice and running water all playing roles and with rocks falling down onto ice or snow and then sliding or settling later on."

Brian is correct when he says that I did not take ice and snow banks into consideration. I was simply asked for my opinion on the orientation of the blocks, and would they have fallen that way naturally. I provided a test that could be readily applied to the material in the excavation; there was no need to involve snow and ice.
Incidentally, in the diagrams comparing the two methods of rocks falling, I included branches and earth beneath the 'human' rock to soften the blow as the rock lands. For some reason these have been erased before posting on the blog.

And finally, Brian says:

"The large block and the rails. Again, I don't agree with Phil. It could perfectly well have fallen and slid on ice or snow into its present position. No human agency needed -- and there are no rails either, as I have pointed out. Has anybody suggested that the longish stones beneath the big "orthostat" are made of mudstone? They look like perfectly ordinary local rhyolite to me....."


In my defence I never suggested that the rails existed, or were made of mudstone.
I proposed that the ‘rails’ be examined to verify whether they were made of the same rhyolite as the igneous outcrop, or of some foreign stone, particularly mudstone.
If there were rails, and if they were formed from mudstone, then these facts would support human activity.

Phil Morgan

BRIAN JOHN said...

Am I being accused of dastardly deeds here, in doctoring Phil's diagrams? I absolutely refute that -- the diagrams were scanned and reproduced exactly as received from Phil.

Constantinos Ragazas said...

“it is unusual that there are four blocks lying at right angles to the rock face. I suggest that a search be made to see if the upper surface of each block correlates with the rock face immediately above it. If it does then it is more likely that it was wrenched from the solid with it rotating about its base as it fell, indicates human activity, (figure 4).”

Brian, how unusual is it for four among hundreds of stones to lie at right angles to the rock face? In both scenarios depicted in Phil's figures 4 and 5 the fallen blocks would lie at right angles to the rock face! And though Phil likes to “suggest that a search be made to see if the upper surface of each block correlates with the rock face immediately above it” I like to suggest this proves nothing! Since the block in Phil's figure 5 could also have flipped over (same as in figure 4) if it were to fall upon some fallen stones and debris pile at the base of the outcrop rock face.

Kostas

Jon Morris said...

"Perhaps Myris knows of any ultrasound scans being carried out."

Thanks Phil. Assuming the original surface is not the result of glacial activity (that is, it remained periglacial in the last ice age), it might have relatively deep cracking?

Must be difficult to know whether or not to spend resources on this sort of thing. On the one hand, a negative result wouldn't particularly prove much one way or the other. However, a positive result (a lack of mid-depth rebound relative to other areas) could be a strong indicator for human activity.

Myris of Alexandria said...

Dear All
No I do not know of any ultrasound activity.
I have to say that I worry about the paucity of mauls.
At BA mining sites throughout the B.Isles they occur in their hundreds/thousands and are often the first indications of mining/quarrying.
Dear Kostas you are forgiven. I am sure zeal is to be encouraged but as the pan-European folk tale Reynadine the Fox tells us 'Be brave, be brave, be very brave, BUT don'tbe too brave. (I heard the very great Louis Killen tell that story -the night of my wedding.He was so right.
News flash Site 8 can represent the WHOLE of the 'quarry' face. So think of it as John The Baptist prefiguring the True Presence.
M

BRIAN JOHN said...

Ah, that's interesting, Myris. So that means that the Jovian fabric of the rhyolite debris at Stonehenge cannot necessarily be tied to one point on the face -- which is apparently what Richard and Mike were discussing on that photo of the experts hard at work......

If this means that it is difficult to distinguish between the fabric on one part of the rock face from that on another part, it will also be difficult to determine exactly where the broken and fallen stones have come from, or which way up they are, or how far they have moved.....

So back to Square One -- some of the debris at Stonehenge has come from somewhere at Craig Rhosyfelin.

Myris of Alexandria said...

No it is more subtle than that, in some orientations the EXACT location is known but in others it is broadened out.
I makes the Jovian discovery all the more remarkable! Trust me!!! the Gods were with us that afternoon.
Shall not say more yet.
It should still be possible, in theory, to match fallen blocks to their original position on the face.
M

chris johnson said...

My feeling is that the quarry folk were expecting to find more evidence. As Myris implies the lack of mauls leads prophets to conclude that working was done elsewhere.

To repeat myself, one of the hammerstones (mauls) was thought to be a spotted dolerite, thus increasing the mist. I wonder whether this is resolved in the meantime, Myris?

m said...

news to me!!
I have not heard that at all or I would have demanded, Thomas-like, to see it.
I have not seen any mauls real or in photos. I have not heard of any other rock type at Cryf but have not asked.
M

BRIAN JOHN said...

Spotted dolerite, or unspotted? I wouldn't be at all surprised to see boulders and cobbles of dolerite at Rhosyfelin, but I might be a bit surprised to find a dolerite with large spots!

Constantinos Ragazas said...

“It should still be possible, in theory, to match fallen blocks to their original position on the face.”

The question however is whether matching “fallen blocks to their original position on the face” can determine 'human agency'. And as Brian has argued and I have argued in my previous post, following Phil's reasoning, it cannot.

What is the “orthostat” at Rhosyfelin doing so far up from “quarry site 8” where the 'Stonehenge connection' is made? And if there is no matching of Stonehenge orthostats to any other quarrying site at Rhosyfelin, what any of this has to do with Stonehenge?

More 'grasping for blocks' ?

Kostas

chris johnson said...

MPP was going to ask Richard Bevins for an expert opinion - he was there that evening.

To my untutored eye it looked spotted and a fine example too.

Constantinos Ragazas said...

Brian,

I am intrigued by the flat smooth polish of the N-W face at Rhosyfelin – with the slightly leaning vertical strata perpendicular to the face.

Could these have been cut and polished by meltwater torrents streaming down that side shaping the smooth N-W side but not the S-E side? And wont that explain all the fallen stones? As it would also explain the soil cover (just a meter? deep) that had them buried – as the stream volume and flow making such deposits eased over time.

Do we really need freeze-thaw to explain the fallen Rhosyfelin blocks? And if we do not, wont this then date the Rhosyfelin “quarry” at a much latter period and perhaps well after Stonehenge? When these grounds were not inundated by a much larger river just further down this point. Otherwise, MPP's “quarry” at Rhosyfelin would have been worked by Neolithic frogmen wearing snorkels, Myris!

Kostas

BRIAN JOHN said...

You may be not far wide of the mark here, Kostas. I have been quite intrigued by the extent of smoothing on the edges of the clutter of boulders and stones (I won't call them orthostats since that encourages the archaeologists) -- I have put up an earlier post on this. Water smoothing is certainly an option -- either flowing water close to an ice edge or else wave action on an oscillating water surface. I am still working on glacial limits in this area, and have a lot of info not yet reported. Suffice to say, for the moment, that Glacial Lake Brynberian is a distinct possibility, round about 20,000 years ago.....

Constantinos Ragazas said...

Brian,

The tapered wear of the NW face – shorter downslope – also indicates to me meltwater torrents were mainly responsible for the polish. The river further down from that point also adds to this impression. So does the larger landscape view in one of your aerial photos. You could clearly make out the outlines of the banks of a larger wider river running through this site and shaping the Rhosyfelin outcrop. And from the looks of this, it doesn't seem to me this wider river existed all that long ago in the past. Possibly postdating Stonehenge. If so, how could Rhosyfelin conceivably be a 'human quarry' for Stonehenge stones? The presence of rhyolite fragments found at Stonehenge and traced to Rhosyfelin must have other more sensible explanations.

Kostas

chris johnson said...

The back of this crag has many rock outcrops which look precarious and anything but smooth - I sent Brian a photo I took some 40 metres from the site along today's river bank.

As a layman on all things geomorphological I have difficulty imagining how these outcrops were NOT demolished by a glacier or eroded by meltwater torrents.

I hope Brian can explain.

Constantinos Ragazas said...

Chris,

I'll let Brian address glaciers … but to your question why Rhosyfelin was not entirely eroded away by torrents, the answer is simple.

The meltwater torrents stopped before they could finish the job! Your observation concerning the SE side as compared to the very smooth and polished NW side confirms the torrents flowed along the NW side, leaving the SE side relatively unaffected.

My sense is this crag was much bigger and higher originally. Perhaps even as high as the top of Preseli. And got eroded down to its present size over time by glaciers or torrents or both. It is plausible MPP's "quarry" may have been under water at the time of the making of Stonehenge!

Kostas

BRIAN JOHN said...

Kostas -- I fear you are getting a bot carried away here -- not for the first time....

Please look at the map. Google will help you.

BRIAN JOHN said...

Sorry -- typing error. I meant "a bit carried away." On second thoughts, more than just a bit...

Constantinos Ragazas said...

Brian,

I don't mind being “a bit carried away” as long as I am moving in the right direction!

Which of my many presumptions are you disputing? Let me guess! The one about MPP's “quarry” being underwater! Did it remind you of Robert Langdon's biblical inundation? No wonder you reacted!

Kostas

chris johnson said...

Dear Kostas, thanks for answering my question.

The idea that the NW face could have been sheered by meltwater seems implausible - the valley does not run in the required direction and nor are there any signs of where it might have gone to after "polishing" the rock face.

Following the face away from the river you come to a big hill and I can imagine some of the scree you can see in the photo was deposited during normal erosion.

Your idea that the quarry site is susceptible to flooding seems more plausible. The land in front of the face is fairly flat and might well be submerged even today should the river be in flood.

I like the sound of Brian's Lake Brynberian. South of the site is a huge natural bowl of land. I suppose he is studying the contours to see where such a lake might have been bounded on the Northern side and where it might have been drained. My guess would be a few miles East where there is a very sharp river valley running towards the Teifi.

The Brynberian river does not look to me like it was shaped by catastrophic natural forces although it would be interesting to know how much water it carried in the recent flood.

I am interested to know which natural forces are most plausibly responsible for the sheer face on the NW - meltwater is unlikely imhau (in my humble amateur opinion).

Constantinos Ragazas said...

Chris,

I think you have listed some likely scenarios for the “polishing” of the NW side of Rhosyfelin. As Brian also has, with his supposition of glacial lake Brynberian. You both have the advantage of being there and seeing the landscape. I can only rely on Brian's photos and descriptions of the land. And what I know convinces me the “polish” was the result of water torrents. The river just off this site, and the immediate contour of the surrounding land (as more clearly seen in the aerial photo Brian posted) all point to this conclusion.

As for meltwater being the source for these torrents, I am only guessing. It may have been other sources of water. Like a glacier lake Bryberian draining with great force. Your observations about features of the landscape seem to suggest this. I would also add the very fragile nature of the rock at Rhosyfelin (as reported by Brian) would make erosion of this crag so much faster. So the idea I suggested Rhosyfelin was a much bigger and taller crag at some time in the past seems very plausible to me.

I realize the details in what I argue may sometimes be wrong; but not essential to my main reasoning. So I ask you consider the larger argument and not hold me to the not-so-relevant details.

Kostas

chris johnson said...

I see today that Brynberian has regular earthquakes - every 50 years at 5-6 on the Richter scale. Google points to a post by Jane Tomlinson about a major earthquake in this area but I could not find it - can anyone shed any light?

Anonymous said...

Chris,
I don't believe earthquakes can explain the NW “polish” of Rhosyfelin. Earthquakes will not sheer off a cliff with just one side. There would be a corresponding other side to that sheer.

Kostas

chris johnson said...

Kostas, I don't want to start a hare running without any support, but had the outcrop sheered in the earthquake way then the other side would be metres underground by now and covered by the eroding material coming down from the hill-side, the surface flattened by regular flooding of the Brynberian river.

Likely all very fanciful, but I am puzzled by the regularity of this rock face in the middle of an irregular environment.

Constantinos Ragazas said...

Chris,

True. The 'other side' of an earthquake sheer could be buried. But how do you explain the very rounded fallen blocks that even Brian expressed amazement and intrigue? I don't believe these could have formed in any other way than through torrents of water running along the NW side and “polishing” it.

Brian's listed possibilities, whether it be “frost-shattering”, “beneath the Devensian ice” or “plucking and entrainment” likewise can't explain such 'facts on the ground'.

So that leaves torrents and the possibility this occurred more recently than Brian believes. My sense is MPP's “quarry” was under water and his “quarry theory” is taking water and will sink!

Kostas

BRIAN JOHN said...

We can't rule out earthquakes as causing some rock face collapses -- they can occur at any time almost anywhere, but I would assume that their frequency would have been greater close to the end of the last glacial episode while unloading / isostatic readjustment was still going on. Whether the great pile of clutter beneath the Rhosyfelin rock face accumulated gradually or as a result of one large collapse is an interesting question. my guess is that there was a slow accumulation under a severe periglacial regime. But the rounding of rock edges on much of the clutter as we see it today is interesting, and is something MPP and his friends should be thinking about.

BRIAN JOHN said...

Re Chris's comment on how clean the rock face is (implying that if it was entirely natural it wouldn't be that clean) I'm not bothered by that at all. If you have a fracture or fault or a bedding plane in sedimentary rocks you can get clean flat faces a great deal more extensive than this one, simply because of the manner in which rocks shear off and fall away from the face of natural weakness. I am aware of similar flat faces all over the place, inland and on the Pembs coast.

m said...

Pity there are no slickensides on the rock face that would have answered that question.
Planar polished faces due to natural causes are Brian says are very very common and why restrict faulting to the last 5000 years we have 100s of million years.
Remember these rocks occur in volcaniclastics and what do we know about volcaniclastic piles??
exactly!in the literature.

BRIAN JOHN said...

That would be nice -- or even some striae......

Constantinos Ragazas said...

Brian et al,

I have also seen “clean flat faces” on rock cliffs that I would not attribute to torrents but to other natural causes. What makes the NW face of Rhosyfelin different and interesting for me, however, is the polished flat NW face is PERPENDICULAR to the vertical strata that make up this crag. I can think of no other natural process that can do this so cleanly and effectively than water torrents. The rounded rock edges of the fallen clutter that Brian speaks about and finds very intriguing also point to this conclusion. And MPP, as Brian strongly suggests, better take mind of this 'fact on the ground'.

Kostas

BRIAN JOHN said...

Kostas -- there are no strata here. This is an igeneous rock, not a sedimentary one. There are fractures and maybe faults -- and one such is the plane away from which the blocks and debris have fallen.

Constantinos Ragazas said...

Brian,

By 'strata' I mean the sections of rock (igneous or any other) between successive fault lines. These 'strata' are clearly visible in all the photos I have seen of Crag Rhosyfelin. Including the photo Chris made of the SE 'hang face'. We also see such 'strata' in all of your photos of the Preseli 'bluestones' overhangs.

At Rhosyfelin, these vertical 'strata' are indeed PERPENDICULAR to the NW “polished” face.

You can fault my use of this word, but you can't fault my logic.

Kostas

Myris of Alexandria said...

I despair Kostas.
Nomenclature is precisely used so that long elaborate explanations are not needed and everyone knows what is being said. DO NOT misuse it. Science is not some new age, charm-swinging, pot smoking, mix and match past time. (not for me anyway, not anymore, done it and still have the stained tee-shirts with burn holes)
Google jointing and foliation.
The planar face is a major foliation plane the other planes are jointing. It is all in Ixer and Bevins 2012 the Arch in Wales paper. Also to the trained eye it is in the aerial photo of Craig etc.
Sorry to pour cold water on your guesses but nothing wet is needed just well-orientated rock samples and a compass-clinometer.
M

Constantinos Ragazas said...

Myris my friend,

I never had the need to have “stained tee-shirts with burn holes”. And though words are important, ideas are more so. An amateur like me can, does, misuse nomenclature. But the essential question here is: can an amateur sometimes see something others (even experts, like your past Ptolemaic rulers) may have missed because of blind spots in their theories?

If “nothing wet is needed” how do you explain the rounded rock edges of the fallen clutter that intrigues Brian? “well-orientated rock samples and a compass-clinometer.” provide no answers here.

Kostas

Constantinos Ragazas said...

Myris, Brian et al,

Consider the photo, http://www.flickr.com/photos/sjorgs/6046643147/ .

For such face to have the same “polish” as the NW face of Rhosyfelin, most likely water torrents would be needed.

Kostas

Anonymous said...

So those who suggest that Rhosyfelin Crags were a quarry for the bluestones, are now reduced to using the "argument from authority". Namely the archeos have asked a professional mining engineer to give his opinion of the site based solely on one e:mailed photograph; being a generous sort he has done so.

I respect Phil's opinion ( I suspect that he has unexpectedly found himself caught in the middle of an argument he didn't ask for)and there is no problem with this per se, but there is when it is presented as scientific evidence to support a hypothesis.

The point I wish to make is as follows. My chums and I have found and explored many kilometers of limestone cave passage within the UK. The exploration of most of these passages has involved the excavation of a considerable quantity of boulders (hundreds of tons).

From experience we have found that it is possible to move boulders of >1 ton in weight using little more than a crow bar and a couple of rock rails consisting of the rock we're digging through.

When you're excavating hard volcanic rocks and have the debitage to hand, the idea that you'd import soft mudstones as rails is "utter bollocks!".

Alex Gee

Myris of Alexandria said...

I am unaware that anyone who is an ardent cryf quarryman has contributed to Brians site ever. Indeed I know they will not and many do not read the site.
Equally I am unaware what Phil's views on the site are but I do think that his suggestions on what data to collect from the face and fallen blocks are important.
I fail to appreciate the import of limestone cave scrambling with or without crowbars has to this debate.
Bye the bye The new paper in Antiquity rather throws a big spanner in the works.
M

Geocur said...

Myris , I never noticed any evidence based spanners relating to transportation glaciation or even a mention of Rhosyfelin , just some relatively minor changes to the sequence . There was however one comment "stones were probably present at the site from it's inception "

BRIAN JOHN said...

Agree with Geo here -- on having a quick glance at the paper I don't see any spanner in the works, let alone a big one......

Anonymous said...

The relevance is yet again why import different rock types to make rails when you have sufficient quantities of rock already present to complete the task in hand???

Myris of Alexandria said...

I cannot now think what the spanner was -it was not a bluestone transport spanner I think it was more temporal than spatial. It was a response to some comment in one of the threads.
Cannot have been of importance.
I quite like the paper and await the time that we know the full Roman remodelling of the Stonehenge Landscape.
M