The shales of the coal measures can be seen sitting on the underlying Millstone sandstone. Once the miners reached this level they knew that there were no more riches below this level, hence the name Farewell. Pontneddfechan stands on the edge of the South Wales Coalfield with the coal seams close to the surface with the coal mining valleys of the Rivers Cynon and Rhondda lying just a few miles to the north east.