The Mary Ann Shaft and the New Engine Shaft worked the Westminster Vein, situated further east from the old Bog Issa Shaft.

The Mary Ann Shaft at SJ 2099 5686 was capped during the 1978 reclamation programme carried out by the NKC Partnership and is now covered by an area of scrap. The shaft is accessible via the track alongside the Bog farm gateway. The area surrounding the shaft and engine house has been cleared of mining waste, which had previously covered a large area as shown on the first edition OS map.

The substantial stone remains of the engine house walls survive to a height of 2.5 meters in parts, located to the north-east of the shaft. The engine house is believed to have featured a stone inscribed with the date 1853. While the features of the engine house are still discernible, the chimney appears to have been cut through by a later track leading to Waendyllog Farm.