This is the left waterfall in the previous image. Look to the right of the falls and you can see the remains of an old steam boiler, a left over from the Rhondda's coal mining heritage. Close to the falls was a coal mine level, sunk into the mountain side around 1869. It became part of the Fernhill Colliery complex. The level produced house coal, probably to be supplied to the houses in the nearby villages of Treherbert. In 1938 the colliery complex employed 1,712 men. It closed in 1978.

History and some photographs here: http://www.welshcoalmines.co.uk/GlamEast/Fernhill.htm