Though all of the rocks which from this geologically unusual hill are Precambrian in age, the relationships between them are not straightforward; several boundaries are geological faults. This close-up shows granophyric granite to the north of the central dip in the ridge.
You are probably looking here at the oldest rocks in Wales. Rubidium-Strontium dating methods have shown these to be 702 (+/- 8) million years old. See also discussion relating to SO2557