"Ynyspenllwch estate papers 1801-1996 - The Ynyspenllwch Estate was a compact estate situated in the parish of Llangyfelach, Glamorgan, bounded by the River Clydach to the west and the Tawe to the south, with Gellionen Mountain and Craig Trebanos at the north and east. Trebanos and much of the present town of Clydach are built on the estate lands." See also below under Land and Property [Archives Network Wales]
"CLYDACH, or Rhyndwyclydach, is a parish and village, .... Ynys penllwch, which is used as a home for Catholic children, is an elegant mansion, standing in its own grounds, surrounded by trees and bounded on one side by the river Tawe ; from the house and grounds can be seen the hills for a long distance on either side of the valley. ..." [From Kelly's South Wales Directory 1923 (ArchiveCDBooks) - transcribed by Gareth Hicks]
Ynyspenllwch estate papers 1801-1996 "The Ynyspenllwch Estate was a compact estate situated in the parish of Llangyfelach, Glamorgan, bounded by the River Clydach to the west and the Tawe to the south, with Gellionen Mountain and Craig Trebanos at the north and east. Trebanos and much of the present town of Clydach are built on the estate lands. The Ynyspenllwch estate was originally a part of the Gnoll Estate, the property of the Mackworth family. The Miers family moved to Wales in the 18th century, settling at Vernon House in the 1760s, and later acquiring the Cadoxton Lodge Estate. The executors of the will of John Miers the younger bought the Ynyspenllwch estate from the widow of Sir Robert Mackworth of Gnoll, Molly Ann Mackworth, formerly Miers............................................"
Ynyspenllwch estate papers 1780-1875 "The Miers' family moved into the Glamorgan area first to Neath c. 1736 and then leased Vernon House in c. 1760. The first John Miers is cited as being of Cannon Street, London, Mitcham, Surrey, and of New Barnstable Hall. They settled at Cadoxton Lodge, Glamorgan, with his son Nathaniel inheriting the estate following the death of John Miers. His early death resulted in the estate passing via his brother John to Nathaniel's son John Nathaniel. The Miers' estate centred mainly in Ynyspenllwch and occupied a compact area situated in the parish of Llangyfelach, Glamorgan. The Ynyspenllwch estate originally formed part of the Gnoll estate, Neath, Glamorgan, before passing into the hands of the Miers family. Molly Ann (daughter of John Nathaniel Miers or Nathaniel Miers) married Robert Humphrey Mackworth of Gnoll and inherited the estate on his death. Shortly after, the estate was purchased by the executors of John Miers the younger [c.1799-1800]. The connections with the Gnoll estate continued, however, with the brothers Richard H. Miers of Ynyspenllwch and Capel Miers of Drumma both acting as Gnoll estate agents"
Miers Estate, records 1735-1882
You can see maps centred on OS grid reference SN695013 (Lat/Lon: 51.695192, -3.889613), Ynyspenllwch which are provided by: