Anglesey and Pembrokeshire -- both subjected to areal scouring?

A comment from a mysterious contributor the other day has got me thinking about the similarities and differences between Anglesey and Pembrokeshire with respect o the history of glaciation.  They are both lowlands located away from the bulk of the Welsh upland massif and its Welsh Ice Cap which waxed and waned during the Devensian glaciation and presumably during other glaciations as well.  In both regions superficial deposits are thin and scattered, and in both regions there are no marked uplands, and instead a sequence of undulating and gentle ridges and depressions which expose the "grain" of the country -- related in turn to the structures and textures of the underlying rock types.

Anglesey has quite prominent streamlined bedrock features, aligned broadly NE - SW, as noted in this article by Lee et al (2015):

Lee, J.R., Wakefield, O.J.W., Phillips, E. & Hughes, L. 2015. Sedimentary and structural evolution of a relict subglacial to subaerial drainage system and its hydrogeological implications: an example from Anglesey, north Wales, UK. Quaternary Science Reviews 109, 88-105.

http://nora.nerc.ac.uk/id/eprint/509384/1/Lee_et_al_QSR_2015.pdf

Quote:

The Quaternary deposits of Anglesey form a thin and discontinuous veneer that mantles the bedrock. The most prominent superficial deposit is a diamicton containing far-travelled erratic lithologies sourced from bedrock strata within and surrounding Irish Sea Basin. This diamicton is synonymous with the ‘Irish Sea till’ (Greenly, 1919; Campbell & Bowen, 1989; Williams, 2003; Thomas & Chiverrell, 2007; Phillips et al., 2010) which forms part of the Irish Sea Coast Subgroup of the Caledonia Glacigenic Group (McMillan & Merritt, 2012). The till was deposited extensively around the Irish Sea Basin by the Irish Sea Ice Stream during the Late Weichselian (Devensian; MIS 2) glaciation (Figure 1c). The overriding of Anglesey and the adjacent offshore area by the Irish Sea Ice Stream led to the sculpting of the substrate and development of streamlined bedrock features (e.g., streamlined bedrock, roche moutonée, rock-cored drumlins) and sediment- to bedrock-cored (e.g. drumlins) subglacial bedforms (Hart 1995; Thomas & Chiverrell, 2007; van Landeghem et al., 2009; Phillips et al., 2010). These landforms and locally-preserved glacial striae record an overall ice-movement direction from northeast to southwest across Anglesey. The Irish Sea Ice Stream was one of several ice streams that drained the interior of the last British Irish Ice Sheet (Figure 1c) (Evans et al., 2005; Bradwell et al., 2008; Hubbard et al., 2009; Clark, C.D. et al., 2012; Clark, J. et al., 2012). At its maximum extent (c.24-23 ka BP) the ice stream occupied much of the Irish Sea Basin and was fed by glaciers emanating from western Britain and eastern Ireland (Knight et al., 1999; Clark & Meehan, 2001; Hiemstra et al., 2006; Roberts et al., 2007; Greenwood & Clark, 2009; Scourse et al., 2009; Rijsdijk et al., 2010; Clark, J. et al., 2012; Chiverrell et al., 2013).

In Pembrokeshire the "grain" of the country is not so easy to pick up, except in the south.  If you look at the following maps, this is apparent. (Google Earth satellite images are not so easy to interpret, because they have too much clutter on them........)

Low definition LANDSAT image of Pembrokeshire.  On this, the grain can be picked up, but it is much clearer in the south.

A simplified map of the structure of Pembrokeshire, with info extracted from BGS mapping material.

The grain can be tied in with the features of the geology map, but note that the strips of Ordovician igneous rocks in the core of the Preseli uplands are NOT easy to pick up in the satellite imagery.

Now let's tie these images in with what we know about directions of ice movement across Pembrokeshire.

This map incorporates information from many sources on ice movement directions, and can be taken as representing a "best fit" for the Anglian Glaciation, around 450,000 years ago.

This map by JC Griffiths (1940) is based on erratic distributions, taking no account of possible zig-zag routes and movements of single erratics across several glacial episodes.  Note that there are differences with the "Anglian" map above.  

Griffiths has Irish Sea ice coming across the north Pembrokeshire coast directly from the north.  He also shows central and southern Pembrokeshire affected by an ice stream flowing from NW towards SE. On the Anglian map we have a more westerly component, with ice moving from WNW towards ESE.

So what is the evidence for streamlining? I have to say that there is none in north Pembrokeshire, but that in south Pembrokeshire there is a degree of alignment between the "grain" of the country, the known structural trends, rock outcrops, and ice movement directions. Cause and effect?  Now that's very difficult to establish.............