Abercwmeiddaw was a slate quarry where slate was produced from the 1840's to 1938 and is located in Corris Uchaf, roughly five miles from Machynlleth. The quarry was connected to the Corris Railway via the Upper Corris Tramway which carried its products to the Cambrian Railway at Machynlleth. The quarry changed owners several times during its working life, and productivity at the quarry varied quite a lot. At the turn of the twentieth century 200 men were recorded as being employed there.
Abercwmeiddaw quarry is notable as being the only quarry in Corris to use a steam engine to move rock on tramways within the quarry. Another distinguishing feature was that an experimental digging machine was used in 1864 on order to create a 'binocular' tunnel - which was unusual at that time.