The ruins of Ponc Twrch Office on the “Ochr Chwith” (left Side) of the Quarry. In the background, you can see some ruins of Ponc Twrch's “Shed gweithio yn oer” (the shed where slabs of slate were reduced in size by manual method). Here the slate called "Hard Grey" would be worked, without help of the saw table.
See the text for references to the Bonc here.