The Flimston erratics — dumped by Devensian ice?

Not so long ago, I believed quite firmly that the erratic memorial stones in Flimston Churchyard (on the Castlemartin Peninsula, Pembs) had been introduced into the area during the Anglian Glaciation — since Devensian ice was assumed not to have affected the area.  Now I’m not so sure, following the discovery of apparently fresh till at numerous localities along the South Pembrokeshire coast.  My working assumption is that the Devensian ice came in from the west, pushing into Carmarthen Bay and probably covering Caldey Island.  At times it might have flowed ENE — indeed, this direction of movement is what seems to be indicated by the reddish (ORS) appearance of the Ballum’s Bay till, since the Devonian reddish sandstones are exposed on the southern part of the island, giving way to Carboniferous Limestone in the north.

My working assumption is that the rampart of cliffs was an efficient barrier to ice movement;  in places the ice overtopped the cliffs, and in places it did not.  South-facing cliffs were affected by ice, and east-facing cliffs may have been left ice-free.  The distribution of clifftop till seems to support this idea.  But.......

Might the Devensian ice have transgressed further inland?  There are abundant records of till and other deposits across the plateau landscape of the Castlemartin Peninsula.  I have always assumed that these are very old.  But if they are uncemented, I now think that they might be of Devensian age.

Back to the boulders.  From Adrian James’s description (below) we can see that the boulders were collected up for use as gravestones or memorial stones from locations up to 3.4 km from the chapel itself, in 1903.  But how heavily weathered are their surfaces?  Here we have a wonderful opportunity for cosmogenic dating.  Let’s assume that since emplacement these boulders have been exposed on the ground surface and not buried in other deposits or covered with vegetation — if they have been lying around since the Anglian glaciation there could be surface exposure ages of up to 450,000 years, but if they are Later Devensian erratics, abraded and modified during ice transport, there could be surface ages as young as 25,000 years BP.

Cosmogenic dating needed........

This map shows the putative Celtic Sea lobe of the Devensian Irish Sea Glacier or Ice Stream pushing eastwards into the Bristol Channel, flowing across Caldey and Lundy Islands and maybe almost reaching the coast of Gower.  Ice is shown just spilling over the cliffs of the South Pembrokeshire coast -- bud did it push much further inland?

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Flimston Chapel churchyard (SR92399558). There is a substantial collection of erratics in this churchyard. Some have been used as headstones for the graves of members of the Lambton Family who died in military service. Others have been left sitting in one corner of the enclosure. All of these stones arrived in the churchyard when the chapel was renovated and re-consecrated in 1903. There are 7 of them. A pamphlet, which describes the features and memorials in the yard, printed at the time of the opening of the chapel in about 1914, gives us these vague details:

No. 1 Boulder, at the head of Lady Victoria Lambton's grave was taken from just opposite Flimston Cottage. A 'brecciated spherulite, albite, trachyte or rhyolite.' Many occur in Pembrokeshire. This one 'seems to fit best with those of Romans' Castle in the character of its spherulites and groundmass.'
[Flimston Cottage stood at SR927955, about 0.3 km ESE of the chapel and just north of the old clay pits.]
No. 2 Boulder, from Pwllslaughter, which stands in the opposite North corner. [Bullslaughter, SR942944 - approximately 2.25 km SE]
No. 3 Boulder from Bulliber Farm [About 2.25 km WNW, at SR905968]
No. 4 Boulder from Merrion pond. [ About 2 km NE].
No. 5 Boulder from Lyserry Farm
No. 6 Boulder from Lyserry Farm.
No.7 Boulder from Lyserry Farm.
[Lyserry is about 3.4 km ENE of Flimston chapel, at SR9556967]