Geology
The summit is formed from Carboniferous Limestone whilst much of the Cefn Cadlan ridge which slopes away to the west is formed from the Twrch Sandstone (formerly known as the Basal Grit), which also dates from the Carboniferous period. A series of minor faults runs northwest to southeast through the hill whilst a few including the Coed Hir Fault run northeast to southwest, paralleling the major fault forming a part of the Neath Disturbance which runs through Cwm Cadlan. Much of the hill's surface is pitted by shakeholes, the larger of which occur on the areas where gritstone forms the surface. Quarries have been opened up in both the limestone and the gritstone over the years though none are now active.
Read more about this topic: Cadair Fawr