This is a great picture -- courtesy Hilary Jensen -- of two of the subglacial meltwater channels near Fishguard. I call them the Criney Channel (on the left) and the Esgyrn Channel (on the right). The photo was taken from a spot near Scleddau.
They belong to the Gwaun-Jordanston system of subglacial meltwater channels, which are very old and which have porobably been used by meltwaters during several glacial episodes. The pattern is very complex, and the channels are "anastomosing" or interconnected. They are steep-sided and flat floored, and most of them are humped in long profile -- a feature indicative of erosion by meltwater under hydrostatic pressure, beneath wasting ice.
The orientation of the meltwater channel system is something of a puzzle, since they suggest an ice surface gradient falling westwards. Most of the evidence of glacial striations and erratic transport suggests an ice surface gradient falling from NW towards SE. Clearly topography has something to do with it, since the Preseli upland must have been a barrier to meltwater flow. I have suggested in the Pembrokeshire Historical Atlas that maybe the channels were cut in the Wolstonian glaciation, at a time when Welsh ice was dominant, flowing broadly westward. But I'm still open to ideas -- watch this space.......
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