The Rhosyfelin Duckpond

Went over to Rhosyfelin today, to check it out for a university group which will shortly be visiting the site.  It looked rather sad, what with all that shredded black plastic after the winter gales.  And the bottom part of the dig is now a duckpond -- well, it is excavated to beneath the seasonal water table, so that's only to be expected......

Some interesting new discoveries, of which more anon.

When is a boulder sufficiently erratic to be an erratic?

I got an interesting query from Andy Burnham on the Megalithic Portal on the subject of the Bowder Stone in Borrowdale near Derwentwater in the Lake District.  It's balanced, apparently very precariously, on one corner.  Somebody had asked whether it could be a glacial erratic (a very big one!) brought down on a glacier from Scotland.  In the  literature there does seem to be some disagreement -- some authorities refer to the massive boulder as local in origin, and others say it is from far away.  Wikipedia says: "The Bowder Stone is a large glacial erratic in Borrowdale. Cumbria, England at grid reference NY25401639. It is estimated to weigh around 2000 tons and is about 9m high, 15m across and 27m in circumference. There is a staircase allowing visitors to climb to the top, and has been since at least 1890."

I have also seen the stone referred to as "the largest standing stone in England" -- but that is nonsense, for it is clearly not an "orthostat" or pillar and it has no archaeological significance.

 I did a bit of digging about, and this was my reply to Andy:

In the Anglian Glaciation, ice from the Southern Uplands must have flowed right across the Lake District, so the transport of large glacial erratics would have been possible. However, it's more uncertain what happened in the Devensian (last) glaciation. Probably there was an ice dome over the Lake District, with radial flow. That having been said, it sounds to me as if the Bowder Stone is made of local volcanic rocks that are found in the vicinity. I found this: "An alternative theory to the Bowder Stone is that it was deposited as a result of a rock fall from nearby crags. There are no abrasions on the rock which would be expected if it were to have been carried by a glacier and the rock is the same rock type as that found at the Hells Wall area of Bouder Crag nearby. The Bowder Stone is a fine grained, Andesite lava rock which was created during the Ordovician period. This has been concluded from its composition of between 65-50 % silica. It is therefore c. 4 million years old and is probably part of the Borrowdale volcanic rock group." The rockfall idea seems reasonable to me! Remember that at the end of a glacial episode one gets a lot of "pressure release" on mountainsides, and it would not be unusual at a time of ice melting for big rockfalls and even landslides to occur in places like this.

Below is a rather sensible description from the Geocaching web site:

Erratic ?

Debate has focused on the geological reasons for its location. Two possible origins have been considered: that it was transported by ice and it is a glacial erratic boulder, OR it fell from the crags above. However the theory that it is a glacial erratic cannot be proven or disproven, there is no evidence that ice from Scotland ever penetrated the Lake District and the stone itself is a piece of Lake District volcanic rock, possibly from nearby Bowder Crag. Ice travelling down Borrowdale from the high fells could have brought the boulder but the Bowder Stone shows no signs of abrasion typical of glacial transport. Also, it is located in the Jaws of Borrowdale, where the valley narrows. Glacier movement speeds up in constricted areas and under such conditions glaciers are more likely to transport boulders rather than deposit them. [BSJ comment:  that's only partially true.  Yes, ice speeds up and erodes more deeply in trough constrictions, but that has no bearing on what is left behind.  When a glacier dies, it dies, and whatever it is carrying will be dumped, close to where it was in the glacier at the time of death!]

Rock fall ?

There is strong evidence that the Stone came to be at its present location because of a massive rock fall. The rock of the Stone and the material in the Hells Wall section of Bowder Crag are identical and its diamond cross-section reflects the pattern of joints in the rocks of Bowder Crag. Also, the rocks on part of Hells Wall have cleavage structures that mirror those on the two large standing stones, which at some time broke away from the Bowder Stone and now lie on its western side. The Stone is just one of many boulders lying on the slope below Bowder Crag and its position at the bottom of this slope is exactly where you would expect to find the largest boulder from a rock fall.
However there is no record of a massive rockfall occurring in historic times. The debris left by it is now completely stable and is today surrounded by dense scrubby woodland. The fall is thought to have occurred at the end of the last period of glaciation in the valley, between 13,500 and 10,000 years ago, when Bowder Crag, weakened by ice action, was subject to constant freeze thaw activity, we do know for definite that the stone is formed of Andesite lava.  [BSJ comment:  That's all very convincing.  I would just add that pressure release and "rock bursting" is a more likely explanation for massive rockfalls than freeze-thaw processes.]

So should we refer to this splendid boulder as an erratic or super-erratic? Yes, I think so.  It's clearly moved a kilometre or so from its place of origin on the cliffs above, and erratics can be emplaced by a wide range of different processes.  We cannot dismiss the possibility that the rockfall that carried the boulder downslope actually dumped it and a lot of other debris onto the surface of a wasting glacier.  That might be possible to elucidate with a bit of field work in the neighbourhood........

The Archaeological Artifice

I have touched on the matter of the "archaeological artifice" before -- and have been thinking about this again today.  It all came back into my mind when I was sorting out some photos to do with Rhosyfelin.

http://brian-mountainman.blogspot.co.uk/2014/09/how-to-manufacture-neolithic-quarry.html

How many ordinary people are aware that when archaeologists, with infinite care, use their little trowels to scrape away fine sediments and leave behind the big bits, they are creating something which can become a pretty vast distortion of reality?  I hope the archaeologists are themselves aware of this danger.........

When you look at the above photo, it's easy for a gullible member of the public to think:  "My goodness!  That looks just like a quarry -- look at the quarried face and all those bits that the quarrymen have removed, just lying there in a big pile, waiting to be sorted out and taken away....."

Actually there never was a natural rock face that looked like this, and this scene never existed in the real world.  When the site was first excavated, there were trees and shrubs everywhere, and a proper mess that the archaeologists, in their wisdom, decided to "tidy up."  This is what it all actually looked like when some of the shrubs had been removed to give access to the accumulated material:

One has to admire the meticulous and fastidious fashion in which the "rubbish" has been removed, leaving only the "significant" stones to be photographed and mapped using the best techniques available.  But the assumption seems to be that the debris is inconvenient and has to be got rid of, and that the bigger stones are important enough to remain in place so as to be examined.  To the right of the top photo, off the picture, there is a huge mound made of all the excavated material........ out of sight and out of mind.

Is there an assumption that the big and convenient stones got there first, as a result of quarrying activities, and that the finer "inconvenient" material then somehow came along later on, covering it all over and filling in all the gaps?

I have also been worried by the "surfaces" which have been spoken of at various stages of the Rhosyfelin dig.  Now in a sequence of sediments surfaces can and do exist, where a soft black layer for example gives way to a hard red layer.  Archaeologists often stop scraping when they get down to a junction, and by stripping away everything above it, they can reveal what might at one time have been the ground surface.  But there is also a great danger that a surface can be invented or created, with archaeologists saying "Ah, in our wisdom we deem there to be some sort of change going on here in the sediment sequence, and we therefore deem it to be a surface."  In the real world, extensive surfaces do not all get covered by newer deposits simultaneously -- bits and pieces may be covered by sedimentation today, leaving other bits exposed until they are covered by some rockfall or other event in maybe hundreds or thousands of years' time.

Sorry guys, but the sequence of events in the real world are much more complex than you like to imagine.  There have been natural slope processes, rockfalls, accumulation events, degradation events, and interference from vegetation here on this site for maybe 20,000 years, and nice photos of a "manufactured quarry", and meticulously drawn plans and diagrams (which we will no doubt soon see in print) do not alter that fact.

The Flat Holm pebble hunt

For the record, this account was written for the Winter Newsletter of the Flat Holm Society, and is now published.
---------------------------

On September 29th 2014 I had a very jolly day on Flat Holm in the company of geologists Sid Howells and Chris Lee, and the Flat Holm tour guides, hunting for erratics and other traces of glaciation. We were blessed with perfect weather and a lack of gulls, so we were able to examine the island quite carefully. The island is important to Quaternary (Ice Age) studies because of its location at the junction between the Bristol Channel and the Severn Estuary, and because there is still great uncertainty about the location and timing of ice limits in this area. We know from studies of glacial deposits that the Irish Sea Glacier has extended at least once well into Somerset. I am a geomorphologist, and I hoped in the company of two geologists we might be able to sort a few things out, and so it proved.

First the shape of the island: it looks like a classic roche moutonnée shaped by overriding ice, with a gentle up-glacier slope on its western flank, and steeper slopes down-glacier to the east. We have to be rather careful about this, because the dipping Carboniferous Limestone strata have obviously played a role, but other evidence also supports the idea that ice has overwhelmed the island, travelling more or less from the west towards the east.

Next, the big erratics: the famous pink erratic at the north end of West Beach is spectacular and easy to spot because of its colour. We have sampled it, but we still do not know where it has come from. Could it have come from Lundy Island? That’s a possibility, but there are a number of other sources of pink granite erratic in the UK, some in Wales and some in Ireland, but the main possible source is in northern England where the Shap granite outcrops. Currently the best professional opinion is that the erratic has come from the Late Pre-Cambrian Coedana Granite outcrop on Anglesey. We cannot tell as yet whether the Flat Holm pink erratic comes from the same source as another famous pink erratic at Saunton in Devon. Chris spotted another large erratic, about 14” across on the north west foreshore. It is a brownish conglomerate, and again we have no idea where it came from. There may well be other erratic boulders with greyish colouring and fine textures, but because of the coincidence with the colouring of local bedrock boulders they are difficult to spot. A more time-consuming survey is clearly needed in the future.

Since there appear to be no identifiable glacial deposits on the island, the real treasures lie on the pebble beaches between the tide marks. From our brief examinations we can say there are literally thousands of erratic pebbles, some derived from destroyed glacial deposits, and some from old river gravels on the floor of the estuary near the island, laid down at times of lower sea levels. Sid took away with him a very heavy load of pebbles including many collected by Linda and other society members, and these are still being identified.

There appear to be two groups of pebbles: relatively local, and far-travelled. The former include limestone, flints, dolomites, purple-brown quarzitic sandstones and shales – the latter are highly variable in lithology. Some, like vein quartz and quartzites, might have come from northern England, for example Carrock Fell. There are also many pebbles made of feldspar porphyry, feldspar-rich lava and silicified welded crystal lithic tuff. In hand samples, Sid already thinks some of these pebbles have come from north west Pembrokeshire, and it might even be possible to identify provenances on Ramsey island. Before we get too excited, thin section work has to be done. But all three of us looking at the pebbles agreed we have not yet seen anything which can be traced with confidence to the eastern part of Preseli, where spitted dolerites and rhyolitic "bluestones" demonstrate a strong link with the bluestone settings at Stonehenge. So a preliminary conclusion might be that the ice stream which crossed Flat Holm might have travelled via western rather than eastern Pembrokeshire.

With reference to our recent discussion, note that the orange band shown on this map more or less coincides with the "eastern Preseli erratic route" which crosses Kenn, Stanton Drew, Heytesbury and Stonehenge.........

When the pebble analysis is complete we will report back, but in the meantime we can say the following. The island has been glaciated at least once by ice travelling from the west rather than from the north. The ice of the Devensian Glaciation (20,000 years ago) probably did not affect the island, although the ice front of Welsh ice was not very far away. It may be that the last glaciation of the island was by the huge Irish Sea Glacier in the Anglian Glaciation, about 450,000 years ago.

I hope to return to do some more work, but in the meantime, thank you for your very kind hospitality and a grand day out.


Brian John

Is Hautville's Quoit a glacial erratic?

I'm happy to open this up for discussion again.  Hautville's Quoit is really a rather interesting boulder.  Only the upper pitted surface is visible today, but when the site was excavated the stone was revealed as a rather irregular boulder made of thin-bedded limestone.  Not sarsen.  There are traces of bivalves in the rock, and this suggested to me that it might be a Jurassic limestone, but I note that Vince thought it might be much older -- namely a Palaeozoic limestone from somewhere further west or north.  Have the bivalves now been identified?

Vince Simmonds's blog site contains a vast amount of useful information.  Greatly recommended:
http://www.sourcingthestones.mendipgeoarch.net/#home

From the photos I have seen, I'm not really all that convinced that there are glacial striations on this stone -- but its shape and overall appearance makes it look to me like a glacial erratic.

What other evidence of provenance or transport mechanisms do we have?  Some of our earlier debate, back in 2012, focussed on whether the pits on the surface might have been man-made.  Geo argued that they seem to be entirely natural, and I would agree with him on that.  The pitting of flat-lying exposed surfaces is something we have discussed with relation to granite in Brittany -- but the same processes of course operate on any flattish rock surface, and in the case of limestone we have an extra process -- solution -- which can crate micro-karstic features like those we see in the photo.

Geoffrey Kellaway

I'm sad -- and not a little ashamed -- to say that I had not realised that Geoffrey Kellaway had died, about 18 months ago.  Below I reproduce the Obituary published on the Geological Society web site. He was an extraordinary man and a great geologist; I suspect that there has never been another geologist with the same intimate knowledge of the country around Bristol and Bath.  I met him at various conferences and field trips, and he was always very helpful in the provision of offprints and hand-written letters providing the information requested.  When I was a research student in 1962-65 he was very approachable and supportive, especially when he realised that I was in the process of doing some damage to assorted very senior geologists for whom he had no great respect!  While he was a very erudite geologist, he was less skilled in matters relating to geomorphology and glaciology, and this led him to make some unfortunate proposals about landscape history which led him into serious trouble and attracted some ridicule.  But he stirred things up very nicely indeed when he published his 1971 paper in NATURE journal on "Glaciation and the Stones of Stonehenge".  I suspect that this paper is far and away his most widely-cited work, and it is full of accurate observations and interesting insights -- even though, as with all papers, there are defects.  It's interesting that in the Obituary below there is only a very brief mention of his contribution to the glacial transport / human transport debate, since it was this one paper which really made him famous and infamous!

He died at the age of 99.  May he rest in peace.

=================================

Geoffrey Arthur Kellaway 1914 - 2013

http://www.geolsoc.org.uk/About/History/Obituaries-2001-onwards/Obituaries-2013/Geoffrey-Arthur-Kellaway-1914--2013/Geoffrey-Arthur-Kellaway-1914--2013-long-version

Outstanding geologist who developed sources of clean hot water for the thermal spas of Bath, England.

Geoffrey (Geoff) Kellaway was born in Bristol, England in 1914 and died aged 99 years in Brighton, Sussex on 18 September 2013. He graduated in 1936 from the University of Bristol with the top first class degree of the Science Faculty. Geoff was a Fellow of the Geological Society for 74 years. He was awarded the Society’s Wollaston Fund in 1950. The excellence of his research was recognised by DSc degrees from the universities of both Bristol and of Bath.

Before he graduated Geoff had already published three papers in the Proceedings of the Bristol Naturalists’ Society, the first in 1932. This first paper is a detailed account of the geology of Bristol, which was then being developed - Geoff taking advantage of the many excavations. He acknowledged help from J W Tutcher (1858-1951), a distinguished Bristol amateur geologist. Tutcher had evidently taught Geoff much about the local geology and encouraged him to write the paper. After graduation, Geoff was awarded a six-month Churchill Scholarship to study geological aspects of the permafrost of Alaska.

Geoff joined the British Geological Survey in 1937. His first assignment was the revision of the Yeovil Sheet of the (then) One-Inch geological map. He moved to the Chepstow Sheet in 1939. In 1940 Geoff was posted to the Northampton Ironstone field, no doubt a result of the wartime concentration of Survey work in areas of economic importance. One result of this was that he was third author of an important paper, with S E Hollingworth and J H Taylor on superficial structures in the area (Quarterly Journal of the Geological Society, 1944, 100, 1-44).

He mapped on the Rutland and Northamptonshire sheets that were published between 1940 and 1946. Geoff moved back to the Bristol area in 1943 and for the next nine years he worked on the Six-Inch geological survey of the Bristol and Somerset Coalfields. He and F B A Welch authored the Bristol District Special One-Inch Sheet which covered the Bristol and Somerset Coalfields and was illustrated by a memoir (British Regional Geology: Bristol and Gloucester, Edition 2, 1948), a very readable and informative introduction to the complex geology of the region for a whole generation of amateur and professional geologists, and subsequently by the Bristol Memoir (Kellaway and Welch, 1993), completed six years after Welch had died and nineteen years after Geoff had retired.

Not the least of Geoff’s contributions was the collection of a large number of detailed sections of mineshafts in the coalfield, some of which were published in Survey Memoirs and others are in the Survey Archives. For many geologists Geoff’s and Frank Welch’s outstanding contribution was the mapping of the Bristol-Somerset and adjacent coalfields. They produced remarkably detailed maps and geological cross sections for the whole of this the most structurally complex coalfield of the UK. This was only made possible by detailed field observations combined with an analysis of complex mine plans and geological logging of a huge number of boreholes and mine shafts and adits.

Desmond Donovan writes:
“I don’t remember when I first met Geoffrey but I think it was after I returned from Army Service in 1946 when he was working on the coalfield revision. He was helpful to a young geologist and we became friends with several interests in common. Later when I was working on the Jurassic boreholes for the Survey I visited the London (Exhibition Road) HQ regularly and if Geoffrey was in the office he would show me his latest ideas on the Bristol area with enthusiasm. He had a large number of maps and diagrams prepared by the Survey drawing office.”

Funded by the Royal Society, he spent a further study period on the permafrost of Alaska and Canada in 1954. His knowledge of periglacial environments was used later in joint papers with other authors on swallow holes in the Chalk, Pleistocene structures in the Cotswolds and landslides in Bath.

Geoff was promoted to District Geologist /Senior Principal Scientific Officer in 1962. He retired from the Geological Survey, by then a component body of the Natural Environment Research Council, in 1974.

In retirement, Geoff undertook a major task which proved to be of great public service. Since Roman times the City of Bath has been famous for its hot springs, which have been used for the alleviation of rheumatism and other medical conditions. The hot springs have been under the care of the Civic Authority since 1590. In 1977 the discovery of the pathogenic amoebae Naegleria fowleri resulted in the closure of the spa water bathing pools and of the pipeline of thermal water to the Royal Mineral Water Hospital, and for the first time since the Roman occupation the thermal springs were not in use by man.

The following outline of Geoff’s contribution to overcoming these problems is summarised from a tribute to him from the Chief Executive (Dr Jo Farrar) and the Leader (Mr Paul Crossley) of Bath and North-East Somerset Council.

“During the period 1977 to 2002 Geoff fulfilled the role of geological adviser to the Council. It is for his expertise, dedication and interest in the Bath Hot Springs that the Council and the people of Bath owe a huge debt of gratitude. During the period 1978 to 1987, Geoff led a multi-disciplinary investigation to find a source of clean water for use in the Pump Room and to enable the Council to realise its vision to restore Spa bathing to the City. The culmination of these efforts was the skilful drilling of an inclined borehole to intercept the flow of thermal water from the King’s Spring where it was proved to be a secure and hygienic source of thermal water.

He helped the Council to revise the Act of Parliament that protects the Bath Hot Springs from damage. His expertise was pivotal in helping the Council to ensure that increased quarrying operations on the Mendips could not have a detrimental impact upon the continued flow of the Hot Springs. Geoff promoted a symposium at the Royal Society to present the results of the multidisciplinary research and edited a definitive review of the research in “The Hot Springs of Bath”. His interest in the hot springs continued undiminished and, originating from the successful proposal to build a new “Millennium Spa” in Bath, he led a further multi-disciplinary investigation into their origin, between 1999 and 2002.

Bath and North-East Somerset Council have been incredibly fortunate to have found a scientist of Geoff’s eminence, energy and commitment to help it to ensure that it fulfils its responsibilities as custodian of the Bath Hot Springs. Without his efforts this historic city would not have a modern spa facility where people can bathe in the United Kingdom’s only Hot Springs.”

Clive McCann writes:
” In 1998 Geoff asked my brother, David, and me to advise on the design of a geophysical investigation of the structure of the Carboniferous Limestone thermal aquifer in and around Bath. With Andrew Mann we supervised a new seismic reflection survey of the urban area of Bath, the reprocessing of existing seismic data of the Radstock basin and the interpretation of gravity and magnetic data. Geoff took a keen interest in the results, leading to excellent and vigorous discussions on the conclusions which could be drawn from the combined data about the origin and routes of the thermal waters to the springs in Bath and Bristol. We were able to publish two papers based on the geophysical data and drawing on the ideas and models which Geoff had previously published.
(McCann, C., Mann, A.C., McCann, D. M. and Kellaway, G.A., 2002, Geological Society Special Publications, 193, 41-52. & McCann, C., Mann, A.C., McCann, D. M. and Kellaway, G.A., 2013, Quarterly Journal of Engineering Geology and Hydrogeology, 46, 267-279.)”

Ramues Gallois writes:
“For those who knew him but did not work with him, Geoff is best remembered as a free thinker whose geological imagination frequently took him down paths that might or might not lead to useful conclusions. He spoke enthusiastically and persuasively about his current ideas, but few made it into print. For those who worked with Geoff the abiding memory will be of his enthusiasm, intellect and his encyclopaedic memory of the rocks and sections that he had worked on. A good example of this last was his recognition of over 1000 errors in the page-proofs of the Bristol Special Memoir, a large number of which were mistakes in the descriptions of borehole/colliery sections.”


Geoff was happy to hold his own in a geological controversy. His 1971 Nature paper on “Glaciation and the Stones of Stonehenge” challenged the idea of human transportation of the stones in favour of a glacial origin and led to a “lively” public debate, particularly with Professor Glyn Daniel (Cambridge University)!

In 1953 Geoff wrote a play “Only a question of time” to be performed at that year’s Geologists’ Dinner using papier-mâché puppets. The text of the play, and the puppets, survive in the archives of the British Geological Survey!

Geoff married Bronwyn in 1939, who died aged 84 years in 1999. He is survived by his two daughters, three grandchildren and two great-grandchildren.


The following websites give a partial list of Dr. Kellaway’s publications.

    • http://envirolib.nerc.ac.uk/olibcgi?infile=authk.glue&style=authk&nh=20calling_page=hitlist.glu&key=81825
    • http://envirolib.nerc.ac.uk/olibcgi?infile=authk.glue&style=authk&nh=20calling_page=hitlist.glu&key=81825
    • BGS archive web pages at: http://www.bgs.ac.uk/services/ngdc/records/archive.html

Other publications not listed on the websites are:

    • Kellaway, G.A. 1996, Discovery of the Avon-Solent Fracture Zone and its relationship to the Bath Hot Springs. Environmental Geology, 28, 34-39.
    • Kellaway, G. A., 2001, Geoffrey of Monmouth’s Historia – A geologists’ view. The Survey of Bath and District, 15, 21-29.
    • McCann, C., Mann, A.C., McCann, D. M. and Kellaway, G.A., 2002, Geophysical investigations of the thermal springs of Bath, England. In: Hiscock, K.M, Rivett, M.O. and Davison, R.M. (eds). Sustainable groundwater Development. Geological Society Special Publications, 193, 41-52.
    • McCann, C., Mann, A.C., McCann, D. M. and Kellaway, G.A., 2013. Insights into the origin of the thermal springs of Bath and Bristol, England from geophysical data. Quarterly Journal of Engineering Geology and Hydrogeology, 46, 267-279.

By Clive McCann, with contributions from Andrew Morrison (Archivist of the British Geological Survey), Geoff’s daughters (Zoe and Ros), Jo Farrar, Paul Crossley, Mark Williams, Desmond Donovan, Ramues Gallois, David McCann and Ted Nield.

Stonehenge's Stone 38

I have been looking over some of the images on the excellent "Stones of Stonehenge" web site, and have realised what a very strange little stone number 38 actually is!  It's the small stone bedded in the ground in the centre of the photo, with a larger sarsen (number 14) lying on top of it.

http://www.stonesofstonehenge.org.uk/search/label/Stone%20038

This stone has been described petrographically in the following paper:

IXER, R.A., BEVINS, R.E. 2011. The detailed petrography of six orthostats from the Bluestone Circle, Stonehenge. WANHM, 104, 1-14.

In shape, it's rather elongated, but no way is it a pillar, or a slab, or a rounded boulder. But it looks natural (with smoothed or abraded edges) rather than "shaped" by human hand. Does anybody have further info on this stone?