In 1870-72, John Marius Wilson's Imperial Gazetteer of England and Wales described Ynyscedwyn like this:
YNYSCEDWYN, a hamlet in the N of Glamorgan; at the confluence of the rivers Tame and Twrch, 13 miles NE by N of Swansea. Iron-works are here; and anthracite abounds in the vicinity, and was brought into use, in 1836, for the blasting of iron.
Additional information about this locality is available for Ystradgynlais
A Vision of Britain through Time includes a large library of local statistics for administrative units. For the best overall sense of how the area containing Ynyscedwyn has changed, please see our redistricted information for the modern district of Powys. More detailed statistical data are available under Units and statistics, which includes both administrative units covering Ynyscedwyn and units named after it.
GB Historical GIS / University of Portsmouth, History of Ynyscedwyn, in Powys and Brecknockshire | Map and description, A Vision of Britain through Time.
Date accessed: 06th December 2013
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