Ferndale No 3 pit was actually in the Rhondda Fawr.
In 1890, when David Davis and Sons - owners of the Ferndale pits, and not to be confused with David Davies of the Barry Railway - became a limited company, it bought Bodringallt Colliery in the Rhondda Fawr and renamed it Ferndale No 3.
Bodringallt was one of the most productive of the steam coal collieries tapping the richer, deeper seams in the Rhondda Fawr, and was located a few hundred metres in a roughly north-westerly direction from present-day Ystrad Rhondda station.
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I am researching coal mining in the Rhonnda Fach. On a map I can find Ferndale pits 1 to 9 but No 3 seems to be missing.