Mapping Mountains – Hill Reclassifications – The 500-Metre Tops of England and Wales – Deweys

Cerrig yr Ieirch (SH 758 425) – Dewey deletion

This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Deweys and where I have had direct association with the status change.  These posts will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the Mountain tables book.

Cerrig yr Ieirch (SH 758 425)

The 500-Metre Tops of England and Wales are affectionately known after their hill list compiler; Michael Dewey.  This list mixes metric and imperial height in its criteria to bookend up to the 2000ft height band and takes in all hills in England, Isle of Man and Wales that are 500m and above and below 2000ft (609.6m) in height that have 30m minimum drop.

This list formed one of a number of lists that appeared in the Mountain tables book published by Constable in 1995 and at the time of publication comprised 373 hills with 164 in England, 5 in the Isle of Man and 204 in Wales.  The Deweys have undergone extensive revision since first publication with the initial stages forming the basis of this revision given below:

1995    Mountain tables published by Constable with 373 hills listed as Deweys.

April 2000    Strider (LDWA quarterly booklet) publishes contact details for David Purchase and Myrddyn Phillips who have found and list 24 and 14 possible new 500m tops respectively.

It was expanded versions of the above two lists that formed the basis of the next publication:

25^th May 2000    List of Possible 500 Metre Tops by Michael Dewey listing 44 hills.

David Purchase expands his Additional Dewey 500m Hills and Myrddyn Phillips produces lists of English 500m hills to measure and Welsh 500m hills to measure.

These lists formed the basis of the next publication:

29^th June 2000    Possible/Probable 500’s by Michael Dewey listing 77 hills.  Michael adopts following protocol; if one person proposes that a top should qualify as a 500 by personal survey, and is then confirmed by a second person, it should then be promoted to the main list.

April 2002    The 500+ Tops of England and Wales – The ‘New Deweys’ published in the Strider booklet and listing 66 new qualifying hills.

25^th May 2006    Rob Woodall republishes Michael’s main and possible/probable lists on the RHB Yahoo group file database. 

Mountain tables by Michael Dewey

The details for this deletion appear below:

The name the hill was listed by in the Deweys is Cerrig yr Ieirch, and it is adjoined to the Arenig group of hills which are situated in the central part of north Wales, and it is positioned with the B4407 road to its north, the A470 road to its west and the B4391 road to its south, and has the village of Ffestiniog towards the west.

This hill was not included in the original 1995 Constable publication, but with a 513m summit spot height and bwlch contouring between 480m – 490m that appear on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps of the day, the interpolated drop value was estimated sufficient for this hill to be a potential new Dewey.

Extract from the Ordnance Survey 1:25,000 Explorer map

The above detail was noted by Myrddyn Phillips and Rob Woodall, with Rob visiting the area of this hill’s bwlch to assess its candidacy for Dewey status and surveying from the bwlch toward a prominent boundary stone close to where the Ordnance Survey place the 490m contour on their maps.  The two then combined to undertake a basic levelling survey of this hill on the 27^th October 2001.  This survey repeated what Rob had previously done with the measurement taken to a path just below the boundary stone to where the 490m contour is placed.  With 23m then added to the result to compensate for the height difference between the 513m summit spot height and the 490m contour, resulting in 100ft / 30.5m of drop.  These details were forwarded to the list author; Michael Dewey and the hill was added to the list on the 2^nd November 2001.

The Leica 530 gathering data at the summit of Cerrig yr Ieirch

The Leica 530 gathering data at the bwlch of Cerrig yr Ieirch

As the result from the basic levelling survey was near the minimum 30m of drop required for qualification to Dewey status this hill was prioritised for a GNSS survey and this took place on the 27^th October 2010.  The summit and bwlch of this hill were surveyed by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica 530 resulting in a 511.0m summit height and a 481.9m bwlch height, with these values giving this hill 29.2m of drop and its subsequent deletion from the list of Deweys.

The full details for the hill are:

Name:  Cerrig yr Ieirch

OS 1:50,000 map:  124

OS 1:25,000 map:  18

Summit Height:  511.0m (converted to OSGM15, Leica 530)

Summit Grid Reference:  SH 75885 42509 (Leica 530)

Bwlch Height:  481.9m (converted to OSGM15, Leica 530)

Bwlch Grid Reference:  SH 77082 41384 (Leica 530)

Drop:  29.2m (Leica 530)

Myrddyn Phillips (September 2020)