|Date||2 July 2011|
|Location||Cwm Croesor||SH 65701 45582; 52.99067°N, 4.00224°W|
Croesor Quarry is located on the Cwm Croesor side of the slopes of Moelwyn Mawr. Slate quarrying at the site dates back to 1846 and in 1864 a connection, via an incline down to the valley floor, was made to the Croesor Tramway, allowing produce to be transported to the port of Porthmadog. Virtually all the workings were below the surface and the relatively small amount of waste visible externally belies the volume of rock actually extracted, as much of the spoil was used to backfill completed excavations. Access to all the workings, on six floors, was via single adit. Unusually, forced, rather than natural, ventilation was employed in the mine and the remains of the fan house can still be seen amongst the surface structure ruins. In order to settle territorial disputes with the neighbouring Rhosydd Quarry, a tunnel was driven between the two quarries so that more accurate surveying could be undertaken.
During the early 20th century a number of innovations were introduced at the quarry under the management of Cornish-born engineer Moses Kellow (1862-1943). Efficiency was improved first by getting the quarrymen to agree to certain changes in the traditional working practices and later by mechanisation.
In 1904 Kellow built a hydroelectric power station at Blaencwm. This was fed by water from Llyn Cwm-y-foel and the electricity generated there powered both lighting and machinery at the quarry and also supplied power to the village of Croesor. (More recently the building was used as an outdoor pursuits centre, but, having been renovated by npower renewables, has now returned to its original function as a hydroelectric power station.)
Elsewhere the slow process of drilling by hand was being replaced by the use of percussive pneumatic rock drills. Kellow, however, developed his own alternative: a hydraulic rotary drill. He made several improvements on his original design, with the final version being produced in 1915. Capable of drilling a 7 ft hole in about 90 seconds, the drill was driven by a turbine powered by high-pressure water and used a water-cooled twist drill bit. The drills were manufactured at the Keldril Works in the mill complex of the quarry itself. Despite its impressive power and efficiency, the Kellow Drill never gained wide acceptance, perhaps due to poor marketing.
Slate production at the quarry came to an end in 1930, and it was later used as a storage facility by Cooke’s Explosives. In the 1920s that company had purchased a site in Penrhyndeudraeth — Gwaith Powdwr — where explosives had been manufactured since 1865. When Cook retired in 1958 the company was acquired by ICI and continued production until 1995. In 1949 Cooke applied for a licence to store explosives at Croesor Quarry, with ICI buying the quarry in 1964.
The three floors below the adit level (‘A’) — ‘B down’, ‘C down’ and ‘D down’ — are all now flooded.