Could the Ramson Cliff erratic have come from Rosslare in SE Ireland?

In the discussion by Daw et al (2026) on the possible origins of the Ramson Cliff Boulder, there is a brief consideration of possible Welsh or Scottish sources, but no mention at all of the possibility that the erratic might have come from the coast of SE Ireland -- more specifically, near Wexford or Rosslare. That is a very peculiar omission, given that the petrological match between the boulder and the 'Rosslare Complex' appears to be far more convincing than the match between the boulder and the Cornubian Batholith rocks.

https://gsi.geodata.gov.ie/downloads/Bedrock/Books/Understanding_Earth_Processes_Rocks_and_Geology_Ireland/Chapter_02.pdf

THE ROSSLARE COMPLEX

The Rosslare Complex is divided into two major units; a group of grey gneisses, coarsely crystalline metamorphic rocks that are well exposed at Kilmore Quay, and a group of dark-green metamorphosed igneous rocks called amphibolites that are seen around Rosslare Harbour and Greenore Point.

(Note: the modern term "amphibolite" is applied to the rocks that are otherwise known as "epidiorite")

The gneisses typically have a banded appearance, in which pale-grey bands of the minerals quartz and feldspar are separated by darker bands rich in mica. These rocks are interpreted as originating as sediments, deposited as a succession of greywacke sandstones and interbedded mudstones. Several periods of metamorphism, under high temperature and pressure conditions deep in the crust, produced the present-day gneisses. In places, thin sheets of granitic composition were injected parallel to the banding in the gneisses. These suggest that particularly high temperatures caused partial melting of the sediments and re-injection of the melted rock as granite.

The metamorphosed igneous rocks are rich in a dark-green mineral called amphibole. They are the metamorphosed equivalents of gabbro and diorite. Although the relationship is not clear, these igneous rocks probably intruded the sedimentary rocks that later became gneisses.

Deformation and metamorphism of the Rosslare Complex were caused by the Cadomian Orogeny of Late Precambrian age, which also affected rocks in southern Britain and northern France. New minerals that grew in the rocks during metamorphism have been dated as 620 million years old, but the gneisses and amphibolites were both already in existence before this time and so were produced by an even earlier metamorphism.

A literature search throws up the point that there are significant greenstone and altered basic complexes in the Wicklow or Wexford areas that align with the path of the Irish Sea Glacier.  Other suggested possibilities are the St David’s area or part of the Gwaun Valley, both of which have basic igneous bodies, though their specific petrography would need to be matched to the erratic. The Bristol Channel Floor has known submerged outcrops of older Variscan basement which might also provide a match, though these are harder to sample.  But for the moment, let's go with Ireland..........

The unconsidered Rosslare case (~600 Ma): The Rosslare Complex (Wexford) is dominated by Cadomian/Avalonian zircon ages, with major peaks around 600–620 Ma. These zircons frequently show metamorphic "resets" or rims from the Ordovician (~480 Ma), reflecting the complex tectonic "squeezing" this region underwent.

The preferred Cornubian case (~290 Ma): Local greenstones associated with the Cornubian Batholith were formed or heavily influenced by the Variscan Orogeny. Their zircon populations are dominated by Early Permian ages.

The petrological match between the Wexford (Rosslare Complex) rocks and the Ramson Cliff erratic is much superior to the Cornubian match because it provides a complete explanation for the rock's ancient, stressed, and complex history—features that are largely absent or localized in the Devon greenstones.
While Daw et al  (2026) favour a local source to support a human-transport theory, the following four petrological reasons demonstrate rather convincingly why Wexford should be considered as a likely provenance:

1. High-Grade Metamorphic Fabric
The Ramson Cliff erratic is a foliated epidiorite/amphibolite, indicating a rock that has been completely structurally reorganized.  In Wexford, the Rosslare Complex is defined by its high-grade, ancient metamorphic rocks. Units like the Greenore Point Group (very close to Rosslare Harbour) consist of strongly foliated amphibolites that were "squeezed" during multiple major mountain-building events. This explains the deep-seated gneissose texture of the rock.  In Cornubia, most Devon "greenstones" are lower-grade greenschists. They are typically massive (lacking a strong fabric) or only weakly sheared. Finding a highly foliated amphibolite in Devon requires searching for very narrow, specific contact zones.

2. The Polyphase Tectonic Story
The erratic shows signs of multiple metamorphic events, with relict minerals overprinted by secondary ones. In Wexford, the Rosslare Complex shows a "polyphase" evolution. It underwent high-grade metamorphism in the Precambrian (~620 Ma), was overprinted in the Ordovician (~480 Ma), and was stressed again in the Variscan. This "messy" internal mineralogy seems to give a match for the erratic’s apparently complex history.  In Cornubia, the Devon greenstones generally show a single, clear Variscan metamorphic event related to the intrusion of the granites. They lack the "deep time" complexity and multiple layers of history found in the Irish basement.

3. Zircon Age Heritage
Petrological identification includes the age and condition of the mineral grains. In Wexford the Rosslare rocks provide a Precambrian (~600–620 Ma) signature. These zircons are often rounded and pitted, matching the "battered" appearance of the crystals in the erratic.   In Cornubia the rocks in question are primarily Variscan (~290 Ma). Even when they contain older cores, their primary "internal clock" is significantly younger.   The degree of recrystallization in the erratic appears more consistent with a rock that has survived 600 million years of history.

4. Geochemical Deep Fingerprints.

Trace element plots are used to identify the original tectonic setting of the parent magma.  In Wexford, the geochemistry of Rosslare's dark gneisses shows tholeiitic signatures consistent with ancient rifting or back-arc basins. This provides a distinct "DNA" that matches the erratic's trace element ratios.  In Cornubia, in contrast, while also tholeiitic in part, the Devon greenstones  show a stronger "continental arc" or "within-plate" alkaline influence, which creates a subtly different slope on
discrimination diagrams.

But, I hear you say, what about the lack of epidote in the Ramson Cliff Boulder, which Daw et al use as a key part of their analysis?  They say that if the boulder had epidote then a western British source would be feasible, but because it is apparently lacking in the one thin section analysed, then the Cornubian source is the only realistic alternative.

=================

Quote from Daw et al, p 15-16:  Other than possible very fine-grained clinozoisite epidote group minerals are absent as are other distinctive secondary minerals including quartz, serpentine minerals, analcime and calcite. Their absence eliminates many altered basic rocks that crop out in western Britain.

.................The alteration of this rock,  notably the lack of epidote, is incompatible with it coming from South Wales (including the Preseli Hills altered dolerites), hence it cannot be a South Welsh 
glacial erratic. Similarly, the absence of analcime and  calcite eliminates other more northern Welsh localities. 

In addition, the petrography and metamorphic grade eliminate it from having a Scottish origin within the British Tertiary Igneous Province despite glacial erratics from that province (but only from the nearby Lundy Granite) being present on nearby Devon beaches. The known Scottish erratics found in  more southern English sites are all petrographically highly distinctive rocks (hence their recognition) 
with characteristic primary and secondary mineral assemblages not recognised in the boulder.

=================

This is all very technical, and I am checking it out with Irish geologists.  Ixer (who wrote the petrographic description) seems to claim that epidote is always found in the altered basic rocks of South Wales, and that if the erratic hade come from North Wales it would have contained analcime and calcite.  He says that "petrography and metamorphic grade" rule out a Scottich origin -- but that is a very vague statement unsupported by hard evidence. If there is evidence, it should have been cited.   Also, I gather from Prof Peter Kokelaar that epidode is NOT ubiquitous in Caledonian Palaeozoic meta-basic rocks -- so to rule out Scotland as a possible source area on that particulat line of evidence would be unwise.  We are told by Ixer that the known Scottish erratics found in southern England are all "petrographically highly distinctive" -- but we are given no information to back up that claim.  The jury is still out.

But from the point of view of glacial geomorphology, a SE Ireland origin for the Ramson Cliff erratic makes perfectly good sense.  I know of only one other positively identified Irish erratic in the Bristol Channel arena -- namely the very hard 'white limestone' boulder found in glacial deposits at Court Hill which is widely assumed to have come from the Ulster White Limestone of County Antrim in Northern Ireland (Gilbertson and Hawkins 1978).  That provenance is entirey reasonable, given what we know about the ice movement directions of the Irish Sea Ice Stream during several glacial episodes.

Could ice have carried Irish erratics from the Rosslare coast out into St George's Channel for incorporation in the Irish Sea Ice Stream, and for transport up the Bristol Channel and onto the Devon coast?  The answer is YES.  That would not involve any provenancing gymnastics -- and is a much more likely scenario than that proposed in the latest article by Daw, Ixer and Madgett.

A provenancing link between the Baggy Point area and Northern Ireland would of course be supported by the biological content and geochemistry of the Fremington Clays and till exposures.  As reported by Gilbertson and Hawkins, Kidson, Stephens and many others, there are strong biological, geochemical and petrological 'markers' in the Fremington clay and till series that indicate that the deposits are not locally originated or derived, but are made of sediments brought in from the N, NW and W -- pointing to one or more incursions of Irish Sea glacier ice.  

Here are some of the maps with reconstructed ice directions in the Celtic Sea arena and the Bristol Channel.  Needless to say, the details are still being worked out -- not just for the older glaciations (Anglian and Wolstonian) but for the LGM as well.

One of my very old maps.  I have been playing with the idea of the Celtic Sea Piedmont Glacier for 60 years or more, and I still think it might explain a few features........

One of my more recent attempts to define the limits of the LGM in this area and the likely directions of ice movement at the time of  'peak glaciation'

One of the BRITICE maps, showing that at one LGM stage (or, more probably. during many stages) ice from the Irish Ice Cap flowed across Wexford and into the St George's Channel.  (Note that this map shows an ice-free corridor over most of Pembrokeshire -- a strange idea which is unsupported by hard evidence and which defies the laws of glaciology.)