Mapping Mountains – Significant Name Changes – Y Pedwarau and Y Trechol – The Dominant Hills of Wales

Mynydd Maen (ST 260 978)

There has been a Significant Name Change to a hill that is listed in the Y Pedwarau and the Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips.

LIDAR image of Mynydd Maen (ST 260 978)

The criteria for the two listings that this name change applies to are:

Y Pedwarau – Welsh hills at or above 400m and below 500m in height that have 30m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to the Mapping Mountains publication of this list appearing on the 30^th January 2017.

Y Trechol - The Dominant Hills of Wales - Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height, with the Introduction to the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The hill is adjoined to the Cymoedd Gwent group of hills which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it is positioned with the A4051 and A4042 roads to its east, the A472 road to its north and the A467 road to its south-west, and has the town of Pont-y-pŵl (Pontypool) towards the north-east. 

The hill appeared in the original Welsh 400m P30 list on Geoff Crowder’s v-g.me website, under the name of Mynydd Twyn-glas, which is a name that appears close to this hill’s summit on contemporary Ordnance Survey maps.

Mynydd Twyn-glas

472m

ST260978

171

152

Marilyn. Clem/Yeaman. Trig pillar.

Hill list authors are prone to list a hill by the name that appears nearest to its summit on contemporary Ordnance Survey maps, without much consideration for its local or historical confirmation, or whether map placement is appropriate, and in the case of this hill the names of Mynydd Twyn-glas and Mynydd Maen have been consistently shown near the summit of this hill on different scaled Ordnance Survey maps.

Extract from the Ordnance Survey 1:50,000 Landranger map

Since publication of these P30 lists on Geoff Crowder’s v-g.me website there have been a number of Ordnance Survey maps made available online, some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website, whilst others are current and digitally updated such as the Vector Map Local hosted on the Geograph website, and which is entitled the Interactive Coverage Map, and in the case of this hill it is the series of Ordnance Survey Six-Inch maps that shows the name of Mynydd Maen being prioritised over that of Mynydd Twyn-glas.

Extract from the Ordnance Survey series of Six-Inch maps

Therefore, the name this hill is now listed by in the Y Pedwarau and the Y Trechol – The Dominant Hills of Wales is Mynydd Maen, and its prioritised status was derived from the Ordnance Survey series of Six-Inch maps.

The full details for the hill are:

Group:  Cymoedd Gwent

Name:  Mynydd Maen

Previously Listed Name:  Mynydd Twyn-glas

OS 1:50,000 map:  171

Summit Height:  473.0m (LIDAR)

Summit Grid Reference:  ST 26000 97841 (LIDAR)

Bwlch Height:  218.0m (LIDAR)

Bwlch Grid Reference:  ST 22547 98878 (LIDAR)

Drop:  255.0m (LIDAR)

Dominance:  53.91% (LIDAR)

Myrddyn Phillips and Aled Williams (July 2019)