Erratic cluster or Neolithic cemetery? I went over to the Llan, near the old primary school in Lampeter Velfrey, yesterday, and found the site rather interesting. One ruined burial chamber, or several? The whole site is so comprehensively destroyed that it's difficult to work out what has been going on -- and the archaeologists are in disagreement about whether there were one, two or three burial chambers here. My money is on three, because there are three large recumbent stones that look large enough to have been capstones.
All of the stones are clearly glacial erratics -- they are heavily abraded and weathered, and have highly irregular shapes. They have clearly just been used because they were lying around in the neighbourhood. The burial chambers must have been very crude. In the assortment of ten stones there are three spotted dolerites (maybe from different sources) and -- lost in the brambles in a mayflower thicket -- three very coarse blue-grey quartz conglomerates. Where have these come from? I'm no expert, but the only extensive conglomerate supposedly found within ten km of this site is the Early Devonian Ridgeway Conglomerate which often has a dark red (ORS) colouring. And that is only exposed to the south of the Ritec Fault. More research needed......
The dark grey conglomerate, packed with quartz pebbles. Something of a mystery....... Ordovician, Silurian, or Devonian?
Re the conglomerate boulders at Llan, there is an outcrop of Cambrian basal quartz conglomerate near St Nons "Follow the footpath from the ruins of St
ReplyDeleteNon’s chapel to the coast path where
you should first look for small outcrops of
Precambrian Halleflinta..It is overlain unconformably
by the steeply dipping Cambrian Caerfai
Group. This comprises a basal quartz
conglomerate which forms a prominent
ridge across the hillside.. http://swga.org.uk/wp-content/uploads/2020/11/Pembrokeshire-Geology-3.pdf
I have seen the ORS conglomerate on the ridgeway near St Florence and it is nothing like the Llan boulders. It's a long time since I saw the St Non's (and Strumble?) material but I recall it as having more similarities. The map of ice movements at the end of this section might suggest that St Davids and/or Strumble head could be a source of the conglomerate erratics at Llan?
Thanks Olwyn -- yes, this one is intriguing. I don't think the conglomerate in these three boulders is anything like the Cambrian basal conglomerate at St Nons. That's seriously colourful -- when I first saw it I thought it was a practical joke or some ornamental concrete created by a mad artist........... these boulders are bluish grey and are very dull by comparison!
ReplyDeleteOh OK! My memory isn't what it was - so many rocks, so many years! I've got a picture of the Llan material, and will keep pondering. I'm sure I've seen something similar somewhere.
ReplyDeleteUnlikely but not impossible source for the conglomerate at Llan? Unlikely but not impossible? http://earthwise.bgs.ac.uk/index.php/File:P006879.jpg
ReplyDeleteIt's possible -- but the illustration does not seem to match the Llan conglomerate boulders -- they seem to have rounded quartz pebbles almost exclusively......
ReplyDeleteNearest match I could find via a Google image search. And the 'Marsett Formation' is to the north and in a glaciated area, near the coast, so in the right direction to potentially be carried down this way by the Irish Sea ice sheet. I do agree it's not identical but there are certainly quartz pebbles in there. I'll shut up now :)
ReplyDelete