There is a lot of coal on Cilfái. This is why it was so important for Swansea’s early industrial economy. Almost all of the original coal workings have been buried or submerged under new trees and vegetation that has grown up since 1970. The Cilfái coal seams dip northwards so that what was originally at the surface above White Rock Copper Works dips underground so that they are underground at Morriston. This is why Copper Pit was so deep, it had to dig down through the glacial debris in the valley and a lot of Pennant Sandstone Rock. The pioneer geologist William Logan taught himself Geology by closely examining the coal seams on Cilfái. Almost two hundered years later, I was able to reconstruct his view of Cilfái coal by reading his notebooks. Here’s my original sketch plan based on his notes
The full story is in Cilfái:Historical Geography
Nigel Robins 