We will be seeing some fun and games over the declaration by MPP et al that one of the recumbent stones at Waun Mawn is made of spotted dolerite and that Richard Bevins has suggested that it came from Mynydd Bach, more than 4 km SE of Waun Mawn. I won't believe that until I see the evidence in print, but it is a bit of a mystery how large ice-abraded boulders of "classic" spotted dolerite apparently got from the spotted dolerite tors like Carg Goedog and Cerrig Marchogion have ended up on the northern edge of the Brynberian moorland at Glanyrafon Uchaf:
These big rounded boulders have certainly not been carted 2 or 3 km from their places of origin by local farmers, since they are of no possible use as gateposts or for anything else -- and so the Preseli ice cap comes into the frame. The boulders look as if they are incorporated into a moraine. Maybe the little ice cap wasn't cold-based and stagnant after all .... ?
Traditionally, spotted dolerites like those above have been deemed by the geologists to have come from Carn Meini, Carn Goedog, Carn Gyfrwy, Carn Bica, Carn Sian, Carn Ddafad-las, or another of the smaller tors on the crest of the ridge. Bit there are plenty of other dolerites outcropping on the mountain which I would call "speckled" rather than "spotted" in that the white spots are less distinct but more numerous. The matrix also appears more flinty and less gritty to the touch. Here is one example, collected just the other day: