Following up on some points made by Peter Kokelaar in his new book "All our own Water" (unfortunate title!), I have been checking out the references to igneous erratics on the Bristol Channel coasts. There are quite a lot of them. Here are some of the localities:
Flimston Churchyard: seven erratic boulders in churchyard, and others nearby. A 'brecciated spherulite, albite, trachyte or rhyolite.' Other volcanic ashes, dolerite and gabbro, from NW Pembs. (Adrian James)
Lydstep, Pembs: gabbro (?) erratic on beach near fresh till outcrop. BSJ observation.
Loveston Farm: dolerite (?) erratic in farmyard, recorded by Adrian James.
Broughton Bay, Gower: green granophyre boulder from Pembs, and possible Leinster granite. (Campbell and Shakesby, QRA 2015)
Butterslade, Gower: non-granite igneous erratics from Pembrokeshire, contained in the Patella Beach deposits. (Jenkins et al, 1985)
Ram Grove Beach, Gower: volcanic and dolerite erratics. (Kokelaar, 2021.)
Hunts Bay, Gower: erratics of quartz dolerite, pink granite and fine grained andesite or basalt of "Irish Sea provenance". (George, 1933)
Reddenhill Farm, nr Pennard, Gower: a coarse-grained diorite erratic (from northern Britain?). Grid ref: SS 536 894. (Kokelaar, 2021)
Western Slade, Gower: several large igneous erratics including a volcanic conglomerate from Skomer Island (?). Grid ref: SS 484 855. (Kokelaar, 2021)
Eastern Slade, Gower: boulders of gabbro and volcanics, probably from Pembrokeshire. (Kokelaar, 2021)
Caswell Bay, Gower: a dolerite erratic 61m above sea-level, probably from Pembrokeshire. Grid ref: SS 595 878. (Kokelaar, 2021)
Cardiff, Ely valley: pyroxenic keratophyre possibly from New Inn, Pembs. (Griffiths, 1940)
Cowbridge, Vale of Glamorgan: 3 boulders of ignimbrite, possibly from Ramsey Island (Bevins and Donnelly, 1992). South of supposed Devensian ice limit. (Are these the same as the 3 blocks of rhyolitic tuff -- up to 30 cms in diameter- found by Briggs in a wall near the cattle market toilets?)
Pentre, near Llantrithyd: tuff from north Pembrokeshire. Vale of Glamorgan - south of Devensian limit (Strahan and Cantrill, 1904)
St Athan: quartz felsite -- north Pembrokeshire origin. Vale of Glamorgan - south of Devensian limit (Strahan and Cantrill, 1904)
Flat Holm: large pink granite erratic boulder and many smaller igneous erratics, including feldspar porphyry, feldspar-rich lava and silicified welded crystal lithic tuff. West Pembrokeshire sources? (John, 2015)
Steepholm: three glacial erratics identified as metamorphic amphibolites (Ixer, letter to Brit Arch 1999)
Lundy Island: erratics on island plateau, including rhyolite and "miscellaneous igneous erratics" (Rolfe et al, 2012).
Kenn, Court Hill and other sites as far east as Bath: basalt, other igneous and metamorphic rocks from the west. (Campbell et al, 1990)
The erratics (giant and otherwise) on the coasts of Devon and Cornwall have not been properly provenanced. Some of the dolerites and rhyolites may have come from Pembrokeshire, but they may also come from further afield -- and I am quite attracted to Kellaway's idea that to the south of the dolerite-bearing stream of the Irish Sea Glacier in Bristol Channel, there was another stream on its southern flank, carrying erratics from as far afield as Scotland.
Giant erratics on the coast of Devon and Cornwall. The Giant's Quoit at Porthleven (above) and the Freshwater Gut boulder near Croyde (below). Origins unknown...........