Sunday, 22 March 2020

Mapping Mountains – Hill Reclassifications – Marilyns



Marilyns – Hill Reclassifications

The Marilyns originally appeared as all hills in Britain that have a drop of at least 150m, irrespective of their height.  Accompanying the main list is a sub-list entitled Submarilyns, with the criteria being all hills in Britain that have 140m and more and below 150m of drop.  The listing of Marilyns was originally published in book format by Cicerone Press in 1992 and entitled The Relative Hills of Britain, its author is Alan Dawson.

The Welsh and then English Marilyns later appeared in two TACit Tables booklets entitled The Hewitts and Marilyns of Wales (February 1997) and The Hewitts and Marilyns of England (June 1997).

The posts that have appeared on Mapping Mountains detailing the hill reclassifications specifically for this list appear below presented chronologically in receding order.








Mapping Mountains - Hill Reclassifications - Marilyns

Moel Oernant (SH 742 340) – Submarilyn addition (9th reclassification)


This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Welsh Marilyns.  These reclassification posts will give details of hills where I have had direct association with their change of status, and they will tie in with a Change Register giving detail to this list and its alterations since publication in the TACit Tables booklet

The listing of Welsh Marilyns was published in booklet format by TACit Tables in February 1997 and entitled The Hewitts and Marilyns of Wales.  The Marilyns were originally listed as an all British compilation and were published by Cicerone Press in 1992 in the book entitled The Relative Hills of Britain.  The list compiler for the Marilyns is Alan Dawson.

When the Welsh Marilyns list was published in booklet format there were 156 qualifying hills with a further 27 Welsh Submarilyns also included.  The criteria for Marilyn status being any hill that has a drop of at least 150m, irrespective of their height, with the criteria for Submarilyn being any hill that has 140m or more and below 150m of drop.

The Hewitts and Marilyns of Wales by Alan Dawson

The details for this addition appear below:

The name of the hill is Moel Oernant, and it is situated in the Arenig group of hills in the central part of north Wales, and is positioned with the A4212 road to its north and the A470 road to its west, and has the village of Trawsfynydd towards the west north-west.

Prior to this hill’s addition to Submarilyn status it was listed with c 138m of drop, based on the 503m summit height which is adjoined to a triangulation pillar and which appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated bwlch height of c 365m based on interpolation of 10m contouring between 360m – 370m.

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

The details for this hill were examined during a re-assessment of the 500m Twmpau list and forwarded to the list author of the Marilyns; Alan Dawson.  The area of this hill’s bwlch was assessed using mapping on the OS Maps website.  This is the replacement for OS Get-a-map and has contours at 5m intervals which are proving consistently more accurate compared to the 5m contours that sometimes appear on Ordnance Survey 1:25,000 Explorer maps and used to appear on the online Vector Map Local.  This mapping has bwlch contours between 360m – 365m with interpolation placing the height of this bwlch at c 362m, resulting in this hill having an estimated drop of c 141m.

Extract from the OS Maps website

These details were forwarded by Myrddyn Phillips via email to the list author of the Marilyns on the 2nd August 2019, and notification received from Alan Dawson via email on the 17th August 2019 that the drop was likely to exceed that required for Submarilyn status.


The full details for the hill are:

Name:  Moel Oernant

OS 1:50,000 map:  124

OS 1:25,000 map:  18

Summit Height:  503m (triangulation pillar)

Summit Grid Reference:  SH 74229 34011 (hand-held GPS via DoBIH)

Bwlch Height:  c 362m (interpolation)

Bwlch Grid Reference:  SN 76134 35148 (interpolation)

Drop:  c 141m (triangulation pillar summit and interpolated bwlch)


Myrddyn Phillips (April 2020)







Mapping Mountains - Hill Reclassifications - Marilyns

Mynydd Bwlch-y-Groes (SN 868 356) – Submarilyn deletion (8th reclassification)


This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Welsh Marilyns.  These reclassification posts will give details of hills where I have had direct association with their change of status, and they will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the TACit Tables booklet

The listing of Welsh Marilyns was published in booklet format by TACit Tables in February 1997 and entitled The Hewitts and Marilyns of Wales.  The Marilyns were originally listed as an all British compilation and were published by Cicerone Press in 1992 in the book entitled The Relative Hills of Britain.  The list compiler for the Marilyns is Alan Dawson.

When the Welsh Marilyns list was published in booklet format there were 156 qualifying hills with a further 27 Welsh Submarilyns also included.  The criteria for Marilyn status being any hill that has a drop of at least 150m, irrespective of their height, with the criteria for Submarilyn being any hill that has 140m or more and below 150m of drop.

The Hewitts and Marilyns of Wales by Alan Dawson

The details for this deletion appear below:

The name of the hill is Mynydd Bwlch-y-Groes, and it is situated in the Mynydd Epynt group of hills in the southern part of mid Wales, and is positioned with the A483 road to its north-west and the A40 road to its south, and has the town of Llanymddyfri (Llandovery) towards the west.

Prior to this hill’s deletion from Submarilyn status it was listed with 140m of drop, based on the 442m summit height which is adjoined to a triangulation pillar and which appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and a bwlch height of 302m based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

Extract from the Ordnance Survey 1:25,000 Explorer map for the bwlch area of this hill

The details for this hill were examined during a re-assessment of the Y Pedwarau – The 400m Hills of Wales list and forwarded to the list author of the Marilyns; Alan Dawson.  The area of this hill’s bwlch was assessed using mapping on the OS Maps website.  This is the replacement for OS Get-a-map and has contours at 5m intervals which are proving consistently more accurate compared to the 5m contours that sometimes appear on Ordnance Survey 1:25,000 Explorer maps and used to appear on the online Vector Map Local.  This mapping has bwlch contours between 305m – 310m with the position of the 302m spot height that appears on the Ordnance Survey 1:25,000 Explorer map below the 305m contour line, indicating that it is not positioned at the critical point of this bwlch.

Extract from the OS Maps website for the bwlch area of this hill

These details were forwarded by Myrddyn Phillips via email to the list author of the Marilyns on the 8th October 2019, and the notification that this hill had been deleted from the status of Submarilyn was received via email from Alan Dawson on the 16th October 2019.


The full details for the hill are:

Name:  Mynydd Bwlch-y-Groes

OS 1:50,000 map:  160

OS 1:25,000 map:  12, 187

Summit Height:  442m (triangulation pillar)

Summit Grid Reference:  SN 86859 35629 (hand-held GPS via DoBIH)

Bwlch Height:  c 305m (interpolation)

Bwlch Grid Reference:  SN 88883 38592 (interpolation)

Drop:  c 137m (triangulation pillar summit and interpolated bwlch)


Myrddyn Phillips (March 2020)






Mapping Mountains - Hill Reclassifications - Marilyns

Coed y Bwnydd (SO 366 069) – Submarilyn addition (7th reclassification)


This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Welsh Marilyns.  These reclassification posts will give details of hills where I have had direct association with their change of status, and they will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the TACit Tables booklet

The listing of Welsh Marilyns was published in booklet format by TACit Tables in February 1997 and entitled The Hewitts and Marilyns of Wales.  The Marilyns were originally listed as an all British compilation and were published by Cicerone Press in 1992 in the book entitled The Relative Hills of Britain.  The list compiler for the Marilyns is Alan Dawson.

When the Welsh Marilyns list was published in booklet format there were 156 qualifying hills with a further 27 Welsh Submarilyns also included.  The criteria for Marilyn status being any hill that has a drop of at least 150m, irrespective of their height, with the criteria for Submarilyn being any hill that has 140m or more and below 150m of drop.

The Hewitts and Marilyns of Wales by Alan Dawson

The details for the hill reclassification appear below:

The name of the hill is Coed y Bwnydd, and it is situated in the Mynyddoedd Duon group of hills in the south-eastern part of Wales, and is positioned with the Afon Wysg (River Usk) and the B4598 road to its west, the A40 road to its north and the A449 road to its east, and has the village of Raglan towards the east north-east and the town of Brynbuga (Usk) towards the south south-east.

Prior to this hill’s reclassification to Submarilyn status it was listed by the name of Clytha Hill with an estimated c 68m of drop based on the 196m spot heights that appear on the Ordnance Survey 1:25,000 Explorer map at SO 36831 06935 and the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map at SO 36738 06931, and an estimated bwlch height of c 128m based on bwlch contouring between 125m – 130m.  

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

LIDAR summit image of Coed y Bwnydd (SO 366 069)

The result produced by LIDAR analysis also affects the adjoining hill named Trostrey Hill (SO 369 051), with LIDAR now showing that Coed y Bwnydd is higher and therefore the respective bylchau positions for each hill are swapped.  The swapping of bylchau has also altered the drop value for each hill, with the caveat that the drop value for the higher hill; Coed y Bwnydd has also been amended as there is a road cutting on the hill to hill traverse.  The LIDAR heights for each summit and bwlch are given below:


Coed y Bwnydd: 

201.0m summit at SO 36613 06921

59.4m bwlch at SO 39307 08899

141.6m drop



Trostrey Hill

199.2m summit at SO 36921 05189

129.0m bwlch at SO 37461 05937

70.2m drop  


LIDAR analysis for Coed y Bwnydd was conducted by Myrddyn Phillips resulting in a summit height of 201.0m positioned at SO 36613 06921 with this position to an embankment that is a part of an ancient hill fort, and the bwlch height is 59.4m positioned at SO 39307 08899 with this position to a road cutting, and the ground of both meets the criteria used within this list.

LIDAR bwlch image for Coed y Bwnydd

The addition of this hill to Submarilyn status was accepted by the list author; Alan Dawson, and its new classification augmented in to the listing of Marilyns in April 2019.


The full details for the hill are:

Name:  Coed y Bwnydd

OS 1:50,000 map:  161

OS 1:25,000 map:  13

Summit Height:  201.0m (LIDAR)

Summit Grid Reference:  SO 36613 06921 (LIDAR)

Bwlch Height:  59.4m (LIDAR)

Bwlch Grid Reference:  SO 39307 08899 (LIDAR)

Drop:  141.6m (LIDAR)


Myrddyn Phillips (March 2020)







Mapping Mountains - Hill Reclassifications - Marilyns

Graig Wen (SH 739 394) – Submarilyn addition (6th reclassification)


This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Welsh Marilyns.  These reclassification posts will give details of hills where I have had direct association with their change of status, and they will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the TACit Tables booklet

The listing of Welsh Marilyns was published in booklet format by TACit Tables in February 1997 and entitled The Hewitts and Marilyns of Wales.  The Marilyns were originally listed as an all British compilation and were published by Cicerone Press in 1992 in the book entitled The Relative Hills of Britain.  The list compiler for the Marilyns is Alan Dawson.

When the Welsh Marilyns list was published in booklet format there were 156 qualifying hills with a further 27 Welsh Submarilyns also included.  The criteria for Marilyn status being any hill that has a drop of at least 150m, irrespective of their height, with the criteria for Submarilyn being any hill that has 140m or more and below 150m of drop.

The Hewitts and Marilyns of Wales by Alan Dawson

The details for the hill reclassification appear below:

The name of the hill is Graig Wen, and it is situated in the Arenig group of hills in the north-western part of Wales, and is positioned with the B4391 road to its north, the A470 road to its west and the A4212 road to its south, and has the village of Ffestiniog towards the north-west and Trawsfynydd towards the south-west.

Prior to this hill’s addition to Submarilyn status it was listed with an estimated c 139m of drop, based on the 556m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger map and an estimated bwlch height of c 417m.

The Trimble GeoXH 6000 set-up position at the summit of Graig Wen 

As its c 139m listed drop was near the benchmark value of 140m it was prioritised for a GNSS survey and this took place on the 1st July 2017 and the 23rd December 2017.  The summit was surveyed on the 1st July by Myrddyn Phillips and Aled Williams and the col was surveyed on the 23rd December by Myrddyn Phillips, using a Trimble GeoXH 6000 with collection times of five and six minutes respectively.  These surveys resulted in a 555.6m summit height and a 414.6m bwlch height, with these values giving this hill 141.0m of drop.

The Trimble GeoXH 6000 gathering data at the bwlch of Graig Wen

The addition of this hill to Submarilyn status was accepted by the list author; Alan Dawson, and its new classification augmented in to the listing of Marilyns in December 2017.


The full details for the hill are:

Name:  Graig Wen

OS 1:50,000 map:  124

OS 1:25,000 map:  18

Summit Height:  555.6m (converted to OSGM15)

Summit Grid Reference:  SH 73910 39474

Bwlch Height:  414.6m (converted to OSGM15)

Bwlch Grid Reference:  SH 76316 40341

Drop:  141.0m


Myrddyn Phillips (March 2020)






Mapping Mountains - Hill Reclassifications - Marilyns

Mynydd Anelog (SH 151 272) – Submarilyn reclassified to Marilyn (5th reclassification)


This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Welsh Marilyns.  These reclassification posts will give details of hills where I have had direct association with their change of status, and they will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the TACit Tables booklet

The listing of Welsh Marilyns was published in booklet format by TACit Tables in February 1997 and entitled The Hewitts and Marilyns of Wales.  The Marilyns were originally listed as an all British compilation and were published by Cicerone Press in 1992 in the book entitled The Relative Hills of Britain.  The list compiler for the Marilyns is Alan Dawson.

When the Welsh Marilyns list was published in booklet format there were 156 qualifying hills with a further 27 Welsh Submarilyns also included.  The criteria for Marilyn status being any hill that has a drop of at least 150m, irrespective of their height, with the criteria for Submarilyn being any hill that has 140m or more and below 150m of drop.

The Hewitts and Marilyns of Wales by Alan Dawson

The details for the hill reclassification appear below:

The name of the hill is Mynydd Anelog, and it is situated in the Pen Llŷn group of hills in the north-western part of Wales, and is positioned with minor roads to its south and east, with the B4413 road further to its east, and has the coast to its immediate west and the small community of Aberdaron towards the east south-east.

Prior to this hill’s reclassification to Marilyn status it was listed as a Submarilyn with an estimated c 149m of drop, based on the 192m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated bwlch height of c 43m.

The Leica GS15 set-up position at the bwlch of Mynydd Anelog

As its c 149m listed drop was near the benchmark value of 150m it was prioritised for a GNSS survey and this took place on the 12th July 2013.  The summit and bwlch of this hill were surveyed by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica GS15 with an hour of data collected at the summit, with Enid Parr, Jeff Parr and Chris Watson also in attendance, resulting in a 191.4m summit height and a 40.4m bwlch height, with these values giving this hill 151.0m of drop.

The Leica GS15 set-up position at the summit of Myndd Anelog

The reclassification of this hill from Submarilyn to Marilyn status was accepted by the list author; Alan Dawson, and its new classification augmented in to the listing of Marilyns in July 2013.


The full details for the hill are:

Name:  Mynydd Anelog

OS 1:50,000 map:  123

OS 1:25,000 map:  253

Summit Height:  191.4m (converted to OSGM15)

Summit Grid Reference:  SH 15193 27218

Bwlch Height:  40.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 17347 28960

Drop:  151.0m


Myrddyn Phillips (February 2020)







Mapping Mountains - Hill Reclassifications - Marilyns

Lovely Seat (SD 879 950) – Marilyn reclassified to Submarilyn (4th reclassification)


This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the English Marilyns.  These reclassification posts will give details of hills where I have had direct association with their change of status, and they will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the TACit Tables booklet

The listing of English Marilyns was published in booklet format by TACit Tables in June 1997 and entitled The Hewitts and Marilyns of England.  The Marilyns were originally listed as an all British compilation and were published by Cicerone Press in 1992 in the book entitled The Relative Hills of Britain.  The list compiler for the Marilyns is Alan Dawson.

When the English Marilyns list was published in booklet format there were 178 qualifying hills with a further 39 English Submarilyns also included.  The criteria for Marilyn status being any hill that has a drop of at least 150m, irrespective of their height, with the criteria for Submarilyn being any hill that has 140m or more and below 150m of drop.

The Hewitts and Marilyns of England by Alan Dawson

The details for the hill reclassification appear below:

The name of the hill is Lovely Seat, and it is situated in the Northern Fells of the Yorkshire Dales, and is positioned with the B6270 road to its north-east and the A684 road to its south-west, and has the small town of Hawes towards the south.

Prior to this hill’s reclassification to Submarilyn status it was listed as a Marilyn with c 150m of drop, based on the 675m summit height that appears as a spot height on the Ordnance Survey 1:50,000 Landranger map and an estimated col height of c 525m based on interpolation of 10m contouring between 520m – 530m.

The Leica 530 gathering data at the col of Lovely Seat

As its c 150m listed drop value was the minimum required for Marilyn status it was prioritised for a GNSS survey and this took place on the 13th May 2010.  The summit and col of this hill were surveyed by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica 530 with 50 minutes of data gathered at each point.  Also present during the survey were Stephen Edwards and Llion Iwan who were filming the proceedings.  The survey resulted in a 674.8m summit height and a 525.7m col height, with these values giving this hill 149.1m of drop.

The Leica 530 gathering data at the summit of Lovely Seat

The reclassification of this hill from Marilyn to Submarilyn status was accepted by the list author; Alan Dawson, and its new classification augmented in to the listing of Marilyns in May 2010.


The full details for the hill are:

Name:  Lovely Seat

OS 1:50,000 map:  98

OS 1:25,000 map:  19, 30

Summit Height:  674.8m (converted to OSGM15)

Summit Grid Reference:  SD 87904 95043

Col Height:  525.7m (converted to OSGM15)

Col Grid Reference:  SD 86824 95469

Drop:  149.1m


Myrddyn Phillips (February 2020)







Mapping Mountains - Hill Reclassifications - Marilyns

Baystones (NY 403 051) – Marilyn reclassified to Submarilyn (3rd reclassification)


This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the English Marilyns.  These reclassification posts will give details of hills where I have had direct association with their change of status, and they will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the TACit Tables booklet

The listing of English Marilyns was published in booklet format by TACit Tables in June 1997 and entitled The Hewitts and Marilyns of England.  The Marilyns were originally listed as an all British compilation and were published by Cicerone Press in 1992 in the book entitled The Relative Hills of Britain.  The list compiler for the Marilyns is Alan Dawson.

When the English Marilyns list was published in booklet format there were 178 qualifying hills with a further 39 English Submarilyns also included.  The criteria for Marilyn status being any hill that has a drop of at least 150m, irrespective of their height, with the criteria for Submarilyn being any hill that has 140m or more and below 150m of drop.

The Hewitts and Marilyns of England by Alan Dawson

The details for the hill reclassification appear below:

The name of the hill is Baystones, and it is situated in the Far Eastern Fells of the Lake District, and is positioned with the A591 road to its west and the A592 road to its east, and has the town of Ambleside towards the west south-west.

The classification of this hill has a convoluted history, as it was originally listed as a Marilyn in the 1992 publication of The Relative Hills of Britain; it was subsequently reclassified to Submarilyn status in 1995 with 149m of drop and then re-instated as a Marilyn in May 2001 with 150m of drop with a 488m summit height and 338m col height based on information Alan Dawson received from Ordnance Survey.

The Leica 530 gathering data at the col of Baystones

As its 150m listed drop value was the minimum required for Marilyn status it was prioritised for a GNSS survey and this took place on the 18th September 2009.  The summit and col of this hill were surveyed by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica 530 with 45 minutes of data gathered at each point.  The survey resulted in a 486.9m summit height and a 339.2m col height, with these values giving this hill 147.7m of drop.

The Leica 530 gathering data at the summit of Baystones

The reclassification of this hill from Marilyn to Submarilyn status was accepted by the list author; Alan Dawson, and its new classification augmented in to the listing of Marilyns and announced on the 11th February 2010.


The full details for the hill are:

Name:  Baystones

OS 1:50,000 map:  90

OS 1:25,000 map:  7

Summit Height:  486.9m (converted to OSGM15)

Summit Grid Reference:  NY 40312 05143

Col Height:  339.2m (converted to OSGM15)

Col Grid Reference:  NY 40614 06556

Drop:  147.7m


Myrddyn Phillips (February 2020)







Mapping Mountains - Hill Reclassifications - Marilyns

Raw Head (SJ 508 548) – Marilyn reclassified to Submarilyn (2nd reclassification)


This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the English Marilyns.  These reclassification posts will give details of hills where I have had direct association with their change of status, and they will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the TACit Tables booklet

The listing of English Marilyns was published in booklet format by TACit Tables in June 1997 and entitled The Hewitts and Marilyns of England.  The Marilyns were originally listed as an all British compilation and were published by Cicerone Press in 1992 in the book entitled The Relative Hills of Britain.  The list compiler for the Marilyns is Alan Dawson.

When the English Marilyns list was published in booklet format there were 178 qualifying hills with a further 39 English Submarilyns also included.  The criteria for Marilyn status being any hill that has a drop of at least 150m, irrespective of their height, with the criteria for Submarilyn being any hill that has 140m or more and below 150m of drop.

The Hewitts and Marilyns of England by Alan Dawson

The details for the hill reclassification appear below:

The name of the hill is Raw Head, and it is situated in the sandstone hills of Cheshire, and is positioned with the A41 road to its west and the A534 road to its south, and has the town of Wrecsam (Wrexham) towards the west and the town of Nantwich towards the east.

Prior to this hill’s reclassification to Submarilyn status it was listed as a Marilyn with 150m of drop based on the 227m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map that is adjoined to a triangulation pillar and a 77m col height.

Gathering data at the col of Raw Head

The Leica 530 set-up position at the col of Raw Head

As its 150m listed drop value was the minimum required for Marilyn status it was prioritised for a GNSS survey and this took place on the 9th and 16th January 2009.  The col was surveyed on the 9th January by John Barnard, Graham Jackson, Janet Jackson and Myrddyn Phillips and the summit was surveyed on the 16th January by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica 530 with various collection times of data from 15 minutes to 40 minutes.  The survey resulted in a 227.1m summit height and a 78.7m col height, with these values giving this hill 148.4m of drop.

Gathering data at the summit of Raw Head

The reclassification of this hill from Marilyn to Submarilyn status was accepted by the list author; Alan Dawson, and its new classification augmented in to the listing of Marilyns and announced on the 16th April 2009.


The full details for the hill are:

Name:  Raw Head

OS 1:50,000 map:  117

OS 1:25,000 map:  257

Summit Height:  227.1m (converted to OSGM15)

Summit Grid Reference:  SJ 50844 54841

Col Height:  78.7m (converted to OSGM15)

Col Grid Reference:  SJ 52870 43921

Drop:  148.4m


Myrddyn Phillips (February 2020)







Mapping Mountains - Hill Reclassifications - Marilyns

Mynydd y Cwm (SJ 073 767) – Submarilyn reclassified to Marilyn (1st reclassification)


This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Welsh Marilyns.  These reclassification posts will give details of hills where I have had direct association with their change of status, and they will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the TACit Tables booklet

The listing of Welsh Marilyns was published in booklet format by TACit Tables in February 1997 and entitled The Hewitts and Marilyns of Wales.  The Marilyns were originally listed as an all British compilation and were published by Cicerone Press in 1992 in the book entitled The Relative Hills of Britain.  The list compiler for the Marilyns is Alan Dawson.

When the Welsh Marilyns list was published in booklet format there were 156 qualifying hills with a further 27 Welsh Submarilyns also included.  The criteria for Marilyn status being any hill that has a drop of at least 150m, irrespective of their height, with the criteria for Submarilyn being any hill that has 140m or more and below 150m of drop.

The Hewitts and Marilyns of Wales by Alan Dawson

The details for the hill reclassification appear below:

The name of the hill is Mynydd y Cwm, and it is situated in the Bryniau Clwyd group of hills in the north-eastern part of Wales, and is positioned with the A5151 road to its north and the A55 road to its south, and has the small city of Llanelwy (St Asaph) towards the south-west.

Prior to this hill’s reclassification to Marilyn status it was listed as a Submarilyn with 149m of drop based on the uppermost 305m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map and the 156m bwlch height that appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.  

The Leica 530 set-up position during the first bwlch survey of Mynydd y Cwm

As its 149m listed drop was near the benchmark value of 150m it was prioritised for a GNSS survey and this took place on the 2nd December 2008.  The summit and bwlch of this hill were surveyed by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica 530 with various collection times of data from 15 minutes to one hour taken.  As the resulting drop value was so close to the benchmark of 150m it was decided to re-visit the hill and gather further data.

The Leica 530 set-up position during the first summit survey of Mynydd y Cwm

The second survey was conducted on the 15th January 2009 by John Barnard, Graham Jackson and Myrddyn Phillips using a Leica 530, resulting in the average from each survey for the summit and bwlch of this hill to be 304.9m summit height and 154.9m bwlch height, with these values giving this hill 150.0m of drop.

The reclassification of this hill from Submarilyn to Marilyn status was accepted by the list author; Alan Dawson, and its new classification augmented in to the listing of Marilyns in April 2009.


The full details for the hill are:

Name:  Mynydd y Cwm

OS 1:50,000 map:  116

OS 1:25,000 map:  264, 265

Summit Height:  304.9m (converted to OSGM15)

Summit Grid Reference:  SJ 07307 76734

Bwlch Height:  154.9m (converted to OSGM15)

Bwlch Grid Reference:  SJ 17432 67786

Drop:  150.0m


Myrddyn Phillips (February 2020)

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