Carn Afr -- and more glaciation traces

Carn Afr is a spectacular hillside tor  at an altitude of 380m n the southern flank of the Presely ridge, only a couple of kilometres away from the hamlet of Rosebush and almost due south from Foelcwmcerwyn summit. Its name can be translated as "the cairn of the goat".  The main feature of the tor is a prominent double pinnacle of rock which is visible from a great distance.  Around it there are small vertical cliffs, grassy steps and clean slabs of rock, with a litter of massive boulders especially to the west. There are several enormous perched boulders near the double pinnacle. 

The rock is for the most part rhyolite, but there are also other foliated or layered volcanic rocks including tuffs and trachyte lava. This is the only substantial tor on Preseli which is made of volcanic rocks belonging to the Sealyham Volcanic Formation, displaced by faulting; all the others are made of rocks belonging to the Fishguard Volcanics. There is only a little scree, at the foot of the lowest of the cliffs. The tor is reminiscent of Plumstone Rock, and it is deeply weathered. It look as if it has been battered by the elements since the beginning of time....... But the lower part of the rocky slope has abundant ice-smoothed outcrops indicative of ice action, with an upper edge around 365 m.

The double pinnacles ar Carn Afr -- visible from many miles away.

Fine-grained light blue/green (silica-rich) rhyolite exposed on the flank of the tor

Flow structures and cavities in the Carn Afr lava

Welded tuffs (?) exposed on a perched block on the lower part of the tor.

As one scrambles down the face of the tor, over a series of steps with minor cliffs and crags, the frequency of ice-moulded surfaces increases, and down on the grassy expanse below, in the vicinity of a striking sheepfold, almost all of the bedrock exposures are moulded and smoothed.

A steeply sloping ice-moulded surface towards the base of the tor, with abundant lichen growth on the surface

Ice-moulded rock exposure near the sheepfold.

Ice-moulded rock surfaces projecting through the turf, west of the sheepfold.

So the impression here is that ice moulding features are not at all marked on the upper paret of this tor, but are prominent on the lower part.  This is not to say that the upper part of the tor was not affected by Late Devensian ice; but it might be that at at some early phase of the last glaciation the whole tor was protected by cold-based ice, and that later on, with the ice surface somewhat lowered, active abrasion and surface modification occurred under a warm-based glacier thermal regime.