Pennant Sandstone erratic

Note from Phil Morgan, for which many thanks:

I've attached a photo of a Pennant Sandstone erratic with the Cynon (Aberdare) Valley, from whence it probably came, in the distance.  This stone is one of three deposited in close proximity to one another on Senghenydd Common, they are clearly visible using satellite imaging (Where's the path = ST 11365  92419,  51.623593, -3.281783).



I don't know the location, and haven't checked the geology or the topography -- but it's a very nice photo of an erratic!  If this is a sandstone, it's a very thin-bedded one -- looks more like a shale or mudstone to me -- but that would be typical of these rocks, which are among the youngest in South Wales -- equivalent of the Upper Coal Measures.