Where has it come from? The best bet is that it has come from somewhere in central Ireland, and limestones rich in braciopods seem to be especially common in the Burren area on the west coast. Here is an example:
However, from what we know of past iceflow directions, a source somewhere near Dublin seems more likely:
Geological map opf Ireland -- the light blue tint shows the area of Carboniferous Limestone outcrops.
If the erratic really did come from Ireland, there must have been much more mixing of ice streams and erratic material in the Cardigan Bay -- St Georges Channel area than has been previously recognized............
We also have to consider Anglesey and the North Wales coast as source areas, although the outcrops there are of very limited extent. This is from the GeoMon Global Geopark web site:
An Anglesey origin for the erratic is, on balance, most likely since this accords most closely with the ice flow pattern shown on the map above.
An interesting dilemma.........
11 comments:
At last, an accurate scaling system. Tell archaeologists!
I don't claim any great virtue on this, Tom. More often than not, I forget to bring my tape measure when I am out in the field, or simply forget to use it........
Trust I will eventually 👍 confirm rumours of a 6 inch (15 cms) piece of bluestone found somewhere on Salisbury Plain......
Time Team's Phil Harding has confirmed he saw the piece of bluestone mentioned in my previous comment. I continue to try to find out where it is now.
Looking at your bottom map, showing the south west of England and Wales, and in particular the area approaching Bath and Wiltshire, reminds me of the Blog Post "The Avon Ice Lobe", 19th August 2014. This has a photograph of the ( now destroyed) Hampton Rocks which were at approx NGR 779666. It was where the Bath - Swindon - London rail line separates from the Bath - Bradford on Avon - Warminster - Southampton line. (continued).
Hi Brian. My Dad suggests Angelsey or Isle of Mann as possible sources?
That photograph of Hampton Rocks is very old and is also unsurprisingly captioned " Bath in Time". The GCR volume map names this feature "Hampton Rocks Cutting". There was discussion as to which direction the glaciation has come from on that Blog Post. I live not far away, and notice that this Post, also that dated 18th December 2009, refer to the Newton St Loe glaciation feature too. We regularly proceed towards Bristol past Newton St Loe. Thus, these two areas of glaciation are noteworthy for overall consideration: Stonehenge is less than 30 miles away.I wonder whether Mike Parker Pearson realises? Is his ruling hypothesis on shaky ground?
Yes Martin -- distinctly possible.
Well, MPP's ruling hypothesis has always been on shaky ground. The Hampton Rocks site has been much disputed, but Kellaway was very convinced of the evidence for an ancient glaciation.
Haven't the Bathampton Down glacial features confirmed glaciation occurred that may have then proceeded towards Salisbury Plain?
They too are very subtle and very degraded. Suggestive of very ancient glacial deposits largely destyroyed by thr passage of time.....
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