Glyn Pits (also known as Glyn Collieries, Nos. 1 and 2 Pits, or Race Colliery) was begun by Capel Hanbury Leigh in the 1840s (NPRN: 33566). Two shafts were sunk side-by-side to a depth of 190 feet (58m), the easternmost shaft the upcast shaft, the other one the downcast shaft. The easternmost shaft was used for pumping as well as winding, the pump rods or spears contained in a compartment to the south of the winding cage guides. The rods were driven by a beam engine installed to the east of the shaft (NPRN: 33729), via a T-bob set in a pit immediately to the west of the shaft-head. Excess water from the workings was raised up to the 80 yard level where it was turned into an adit and flowed by gravity to exit in the valley bottom. In later years pumping was carried out using electric pumps supplied from a brick-built transformer house that lies to the north of the shafts.

Above the shafts there was formerly a timber-built tandem head frame with a winding sheave above each shaft. This was later replaced by a steel structure, the feet of which are still visible close to the shaft rims. Originally the beam engine was used for both winding and pumping functions, by 1865 a second engine (NPRN: 33730) to the north east of the upcast shaft took over the winding function.

Latterly ventilation of the shafts was by a Scirocco type fan. A brick, barrel vaulted tunnel inclined upwards, westwards from the upcast shaft, its end shut off by a series of air-sealed doors. On the south side, a side tunnel led to a compartment in which the fan was installed. The fan was driven by a small steam engine. The brick tunnel, minus its doors, is still extant, as is the fan machinery. The steam engine has gone but its position east of the fan is still discernable.

A detailed survey of the colliery was undertaken by RCAHMW during 2005-2006.

Sources
Tilley, G 2005 The Surviving Engines of Glyn Pits, Pontypool: Early Steam and Water Power in Local Industry.
Palmer, M & Neaverson, P 1990 `The Steam Engines at Glyn Pits Colliery, Ponypool: an Archaeological Investigation'. Industrial Archaeology Review: 13, 7-34.

David Percival & Louise Barker, RCAHMW, March 2007.