The great passage grave hunt

Passage graves?   Photos:  courtesy Emyr Jones

Following a mention in one of the local archaeology newsletters, there has been a flurry of activity here in North Pembrokeshire as people of all ages and levels of expertise go off hunting for passage graves on Brynberian Moor.  I was alerted to this by Emyr Jones, who has stimulated a lot of discussion on social media.

The approx grid references for the features found by Emyr and his friends are SN 095338 and SN 087332.  One of the features is near a prominent hawthorn tree on the moor, and the other is not far from the edge of a recently burnt area.

This is a part of the moor which is not visited very often, lying on the flank of the great moraine which I have described in earlier posts in the vicinity of Tafarn y Bwlch.  On the OS map the area is referred to as Banc Llwydlos.

I shall go and take a look, and report back......

Above is a Google earth image of the Banc Llwydlos area -- a big and boggy wilderness area of several sq km with extensive tracts of gorse, bracken and wetland.  Needle in haystack territory -- but this is the best time of year to go searching, before the bracken gets high.

On the image above Tafarn y Bwlch is on the extreme left, and the big farm is Penanty-isaf.  The stream catchment is that of the Afon Pennant, which flows down towards Brynberian vallage and the Brynberian river gorge.

The creation of the Straits of Dover

 https://www.researchgate.net/blog/post/britain-would-still-be-attached-to-europe-had-this-ridge-remained-intact


This is an interesting article -- I have not yet managed to read the original in "Nature Communications".  The idea of the Ice Age megaflood draining a pro-glacial lake in the southern North Sea is an old one, and Gupta and his colleagues have been reporting on the essentials of this work for more than 10 years now.  What is new is the linking of the megaflood event with the gigantic depressions (up to 100m deep) close to the position of the old chalk ridge that ran across from one side to the other.  They are now interpreted as plunge pools created by enormous volumes of meltwater cascading over the low points in the ridge.

On the illustration above, note the herd of rhinos..... nice touch!

It looks as if the original breach of this chalk ridge is now assumed to have occurred at the end of the Anglian Glaciation, around 500,000 years ago.   We have talked rather a lot about that particular glaciation on this blog.......

It's always good to see some serious glacial geomorphology given some publicity by the BBC and other media -- but calling the "megaflood event" an Ice Age Brexit really is taking things a bit far.  Has the whole world gone bonkers?  Well, yes........

Foel Drygarn fortified settlement

Here is another fabulous image from the Bing satellite coverage.  It shows the Foel Drygarn hillfort / fortified settlement at the eastern end off the Mynydd Preseli upland ridge.

You can see very clearly the three Bronze age burial mounds, the main Iron Age (?) fortified site enclosed by an embankment (with the pitted surface showing where the huts were located), the subsidiary embanked area to the north (with more hut circles), and the animal enclosure (?) on the NW flank of the inhabited area. 

"Foel Drygarn" means "the bare hill with three cairns".

The edge of the Preseli Ice Cap?

Wizard wheeze for today.  New theory for us to mull over.

For some time I have been intrigued by what has gone on in the past in the southern foothills of Mynydd Preseli, in the zone that includes Rosebush, Maenclochog, Llandilo, Llangolman, Efailwen and Llanfyrnach.  There is a line in the landscape -- irregular, but quite distinct.   The thing that puzzles me in particular is the fact that to the north of this line there are no deeply cut valleys or gorges, but to the south of it we see a string of deeply cut winding valleys with some interesting features including connecting valleys and blunt-headed small tributaries. I cannot see any geological or structural reason for this contrast.  Could it be that the line connecting these "valley heads" represents a stillstand along the edge of a small Preseli ice cap?  We know that there are meltwater gravels at Rosebush and Llangolman -- I shall check out whether there are any others........  watch this space.

The valleys do not seem to be similar to those of the Gwaun - Jordanston meltwater channel system, which displays two features indicative of subglacial meltwater flow: an anastomosing pattern and humped long profiles.  The channels between Rosebush and Efailwen appear to be subaerial ones, which carried large torrents of meltwater southwards into the Eastern Cleddau catchment.

The satellite image, by the way, is from the Bing satellite coverage, with a slightly distorted "landscape"view.  It shows up the river gorges very well.

Postscript:

Here is a superficial geology map of the area, from the Geology of Britain Viewer.  It shows the occurrence of patches of sands and gravels mostly inside the line drawn on the image above.  Significant, or not?  We shall see......

POSTSCRIPT

Adding here the model by Henry Patton and his colleagues showing the theoretical extent of the Preseli Ice Cap at 23,850 yrs BP -- at the time of its proposed maximum extent.  The southern margin is very similar indeed to that which I am now proposing on geomorphological grounds.  What will be much more difficult to work out is the relationship between this little ice cap and the powerful Irish Sea Glacier which came in from the N and NW.  When did the two ice masses make contact, and what happened in the contact zone?  Did that contact zone oscillate over space and time?

Carn Meini and the Stone River

I'm more and more impressed with the quality of the satellite imagery on Bing.  Take a look here:
https://www.bing.com/maps/

This is a wonderful image of the Carn Meini (Carn Menyn) area showing the tors and the nearby "Stone River" (to the left) which some people insist on interpreting as an ancient trackway, without ever going to check out what it looks like............

I interpret it as a stone stream -- partly a periglacial feature, also used as a stream bed -- with much of the finer material washed out, leaving a "boulder bed" behind.

The quality of these Bing images is amazing -- and the small details in the landscape are enhanced by the low sun, giving rise to long shadows.

Earthfast Neolithic tomb, St David's Head

The famous cromlech near the tip of St David's Head, found in close proximity to an Iron Age fortified settlement site.  Strictly, this should be referred to as an earthfast tomb, since one end of the capstone has been levered up and then propped, but the other end still rests on the ground.  As usual, the guiding principle seems to have been economy of effort -- this big flattish stone was simply used where it was found.

St David's Head -- ice-moulded terrain

Ice moulded terrain near the outer tip of St David's Head.  The moulding may not all be due to the effects of the Devensian Irish Sea Glacier moving in from the NW, but the "cleaning up" of the surface almost certainly is.......

More ice-moulded surfaces on the north coast near St David's Head, looking towards Carn Llidi

Ice-moulded surface (glaciated slabs) near Carn Llidi

More ice moulding, on the summit of Carn Llidi 

The above images are all from the Google Streetview coverage of the Pembrokeshire Coast Path  -- the definition is a bit fuzzy, but the main features of the landscape are pretty well portrayed.