In 1870-72, John Marius Wilson's Imperial Gazetteer of England and Wales described Bryn Mawr like this:
BRYNMAWR, a large seat of iron-works, on the northern border of Monmouth; on the Merthyr and Abergavenny railway, in the vicinity of Nantyglo. It has a post office‡ under Tredegar, a r. station, an inn, a church, and several chapels. A railway from it to Blaenavon was authorised in 1866.
GB Historical GIS / University of Portsmouth, History of Bryn Mawr, in Blaenau Gwent and Brecknockshire | Map and description, A Vision of Britain through Time.
Date accessed: 29th March 2017
Click here for more detailed advice on finding places within A Vision of Britain through Time , and maybe some references to other places called " Bryn Mawr ".