List of geological faults of Wales explained

This is a list of the named geological faults affecting the rocks of Wales. See the main article on faults for a fuller treatment of fault types and nomenclature but in brief, the main types are normal faults, reverse faults, thrusts or thrust faults and strike-slip faults. Many faults may have acted as both normal faults at one time and as reverse or thrust faults at another and may or may not have also incorporated some degree of strike-slip movement too. Fault zones, fault belts and fault complexes typically describe assemblages of faults which have a common origin and history and whose alignments tend to be sub-parallel to one another.

There are also a number of 'disturbances', notably in South Wales. These linear features are a combination of faults and folds - the relative importance of faulting and folding varying along the length of each disturbance.

Key to tables

Alphabetical lists of faults

A

Fault name OS map refCountyBGS map sheetbook references
Gwynedd Brenchley & Rawson 2006
Aber Fault Glamorganshire E&W 248
Aber Richard FaultE&W 194; 210
Aberbeeg Fault Mem E&W 232
Aberdaron Fault Gwynedd E&W 133
Abergwesyn FaultE&W 196, 212
Abertillery FaultE&W 249 Mem E&W 232
Abertridwr FaultGlamorganshire E&W 249
Acorn Fault E&W 230
Afon Banwy Fault Powys E&W 150
Afon Ganol Fault Clwyd Mem E&W 95/107
Afon Saint Fault Gwynedd E&W 133
Allt y Crib FaultE&W 163
Allt y Grug Fault E&W 230
Alyn Valley Fault E&W 108
Anafon Fault Gwynedd E&W 106
Arthog - Caerdeon Fault E&W 149
Axton Fault Flintshire E&W 96

B

Fault name OS map refCountyBGS map sheetbook references
Smith et al. 2005
E&W 135; 136
Bala Fault Zone UK (south) 625K
Gwynedd E&W 119
Beech Hill Fault Monmouthshire Usk-Cwm:25K
Belmont Fault Clwyd Mem E&W 95/107
Pembrokeshire E&W 228 Brenchley & Rawson 2006
Berach Fault E&W 230
Anglesey Brenchley & Rawson 2006
Berw Fault Complex Anglesey Brenchley & Rawson 2006
Bethel Fault Glamorganshire E&W 247
Bettws FaultE&W 230
Bettws Newydd FaultMem E&W 232
Blaenavon Fault Monmouthshire E&W 232
Blaenhirwaun Thrust E&W 230
Blaen Onneu FaultE&W 232
Bodafon Thrust Anglesey Brenchley & Rawson 2006
Bodelwyddan Fault Denbighshire E&W 95; 107 Mem E&W 95/107
Box FaultGlamorganshire E&W 247
Bristol Channel
Ceredigion E&W 178; 210; 211
Ceredigion E&W 194; 195
Brothers Fault Glamorganshire E&W 247
Brwynd Overthrust E&W 163
Bryn Eglwys Fault E&W 120 Brenchley & Rawson 2006
Bryn Morgan ThrustE&W 230
Bryn Posteg Fault E&W 164
Bryn Rhys Fault Clwyd Mem E&W 95/107
Brynderi Fault Monmouthshire Mem E&W 233/250
E&W 121
Bryngwili FaultE&W 230
Bryngwyn Fault Glamorganshire E&W 230; 247
Bryn-y-maen FaultDenbighshire E&W 95
Bwlchgwyn FaultE&W 108
Bylchau Fault Denbighshire E&W 107 Mem E&W 95/107

C

Fault name OS map refCountyBGS map sheetbook references
Cae Parc Fault Glamorganshire E&W 247
Caerdeon Bodlyn Fault Merionethshire E&W 135
Caergwrle Fault E&W 108
Caerleon FaultMonmouthshire E&W 249; Usk-Cwm:25K
Caerphilly Fault Glamorganshire E&W 249
Camdwr Fault E&W 163
Capel Garmon FaultClwyd E&W 107 Mem E&W 95/107
Cardigan - Fishguard Fault Belt Pembrokeshire E&W 210
Carmel Fault (Powys)Powys E&W 179
Carmel Fault (Carmarthenshire)Carmarthenshire E&W 230
UK (south) 625K Brenchley & Rawson 2006
Carreg Maen Taro FaultE&W 232
Carrog Valley Fault Ceredigion E&W 178
Cascade OverthrustE&W 163
Castell FaultE&W 163 Mem E&W 165/151
Cefn Fault Clwyd Mem E&W 95/107
Cefncynfal Fault Powys Mem E&W 165/1051
Cefn Bryn Thrust Glamorganshire E&W 246
Cefn Crib Fault GlamorganshireE&W 249
Cefn FaultE&W 107
Cefn Garw Fault Monmouthshire Mem E&W 233/250
Cefn Ila Fault Monmouthshire Usk-Cwm:25K E&W 232
Cefnamwlch-Rhiw Fault Gwynedd E&W 134
E&W 193
Ceidio Fault Anglesey Brenchley & Rawson 2006
Ceunant Fault E&W 149
Chapel Fault E&W 231
Chepstow Fault Monmouthshire Mem E&W 233/250
Brenchley & Rawson 2006
E&W 213 Mem E&W 165/151
Cilfeigan Fault Monmouthshire E&W 249; Usk-Cwm:25K
E&W 179
Clochaenog Fault Clwyd Mem E&W 95/107
Smith et al. 2005
Clydach Bridge Fault Monmouthshire E&W 232
Clywedog FaultE&W 164
Clytha FaultE&W 232
Coalbrook Fault E&W 230
Coed Hir FaultE&W 231
Coed Ithel FaultMonmouthshire Mem E&W 233/250
Coedycerrig FaultE&W 232
Coed-y-paen FaultMonmouthshire E&W 249; Usk-Cwm:25K
Conwy Valley Fault/Conway Valley Fault Gwynedd E&W 106 Mem E&W 95/107
Copper Works FaultGlamorganshire E&W 247
Cors-bol FaultAnglesey Brenchley & Rawson 2006
Craig Twrch Fault E&W 212
Craiglaseithin FaultGwynedd E&W 135/149
Craignant - Milton FaultSmith et al. 2005
Craignant Fault Smith et al. 2005
Craig-y-beri FaultE&W 137
Craig-y-glyn FaultE&W 137
Creigydd FaultMonmouthshire E&W 249; Usk-Cwm:25K
E&W 213
Crick Fault Monmouthshire Mem E&W 233/250
Cross Ash FaultMonmouthshire Mem E&W 233/250
Crychan Fault Powys E&W 196, 213
Crychan Fault Belt E&W 213
Cwm Cayo Brook Fault Monmouthshire Mem E&W 233/250
Cwm Cynnen Fault E&W 211
Cwm Dockin FaultE&W 165
Cwm Dwfnant FaultE&W 196
Cwm Earl FaultE&W 165
Cwm Felin Fault Glamorganshire E&W 247
Cwm Llwyd FaultE&W 230
Brenchley & Rawson 2006
Cwm Pit Fault Glamorganshire E&W 247
Cwm Sylwi FaultE&W 149; 163
Cwmcarvan Fault Monmouthshire Mem E&W 233/250
Cwmdockin Fault PowysMem E&W 151/165
Cwm-dows Fault Glamorganshire E&W 249
Cwmgwineu Fault Glamorganshire E&W 247
Cwmllynfell Fault E&W 230
Cwm-Mawr Fault E&W 196
Cwmmawr Thrust E&W 230
Cwmneol Faul E&W 231
Cymmer Fault Glamorganshire E&W 248
Cynheidre Thrust E&W 230
Cynllaith Fault E&W 137

D

Fault name OS map refCountyBGS map sheetbook references
Daren Ddu Fault Glamorganshire E&W 249
Daron Fault Gwynedd E&W 133
Denbigh Fault Clwyd E&W 107 Mem E&W 95/107
Dinas Fault (Powys) Powys E&W 231
Dinas Fault (Glams) Glamorganshire E&W 248
Dinorwic Fault Gwynedd E&W 106
Dip Fach Fault E&W 231
Dolforwyn Fault E&W 165 Mem E&W 151/165
Dolwar Fault Powys E&W 150
Dowlais Fault (Mons) Monmouthshire E&W 231; 232
Dowlais Fault (Glams)Glamorganshire E&W 249
Duffryn FaultGlamorganshire E&W 230, 247
Dulas Fault E&W 196
Dulas Gap Fault Denbighshire E&W 95; 107 Mem E&W 95/107
Dyffryn Maelor Fault Clwyd Mem E&W 95/107
Dyfi Valley Fault Powys E&W 150
Dyfnant Fault Powys E&W 150
Dyfngwm Fault E&W 164
Dylife Esgairgaled Fault E&W 164
Dylife Fault E&W 164
Dynant Fault E&W 230
Dysynni Fault E&W 149
Dyto Fault Clwyd Mem E&W 95/107

E

Fault name OS map refCountyBGS map sheetbook references
East Llangerniew Fault Clwyd E&W 107 Mem E&W 95/107
Efailnewydd Fault Gwynedd E&W 134
Eglwysbach Fault Clwyd Mem E&W 95/107
Energlyn Fault Glamorganshire E&W 249
Erroxhill Fault Pembrokeshire E&W 228

F

Fault name OS map refCountyBGS map sheetbook references
Felin Arw Fault Glamorganshire E&W 248
Ferry Fault Glamorganshire E&W 247
Flint Fault E&W 108
Forge Overthrust E&W 149; 163

G

Fault name OS map refCountyBGS map sheetbook references
Gadlys Fault Glamorganshire E&W 231; 248
Gardeners Fault Glamorganshire E&W 230; 247
Garth - Llanwrtyd Fault Belt E&W 212
Garth Fault E&W 196, 213
Garth Ferry Fault Anglesey Brenchley & Rawson 2006
Garth Hill Overthrust Glamorganshire E&W 249
Gelli Fault Glamorganshire E&W 249
Gelligaer Fault Glamorganshire E&W 249
Gelli-goch Overthrust E&W 149; 163
Giant's Grave Fault Glamorganshire E&W 247
Glan Hafren Fault E&W 165 Mem E&W 151/165
Glanalders Fault E&W 179
Glandyfi Fault E&W 163
Glaslyn Valley Fault Brenchley & Rawson 2006
Glyn Ceiriog Fault E&W 121
Glyn Fault Monmouthshire E&W 249; Usk-Cwm:25K
Glyn Valley Fault E&W 135
Glyn Wallis Fault E&W 230
Glyncorrwg Fault Glamorganshire E&W 231; 248
Gnoll Fault Glamorganshire E&W 247
Gop Fault Flintshire E&W 95 Mem E&W 95/107
Gors Fault Glamorganshire E&W 230, 247
Gorsedd Bran Fault Clwyd Mem E&W 95/107
Gorseinon Fault Glamorganshire E&W 247
Great Ewloe Fault E&W 108
Greenland Fault Monmouthshire E&W 232
Gresford Fault E&W 121
Grib Fault E&W 230
Groes Fault Clwyd E&W 107 Mem E&W 95/107
Grovesend Fault Glamorganshire E&W 230; 247
Guilsfield Fault Powys E&W 150, 151 Mem E&W 151/165
Gwaynynog Fault Clwyd E&W 107 Mem E&W 95/107
Gwern-ddu Fault Monmouthshire Mem E&W 233/250
Gwespyr Fault Flintshire E&W 96
Gwili Fault Glamorganshire E&W 230, 247
Gwrych Castle Fault Denbighshire E&W 95; 107 Mem E&W 95/107
Gyrnos Fault E&W 231

H

Fault name OS map refCountyBGS map sheetbook references
Hafan Fault E&W 163
Hawarden Fault E&W 108
Hendre Fault E&W 230
Highgate Fault Powys E&W 164; 165 Mem E&W 151/165
Hirwaun No 1 Fault E&W 231
Hirwaun No 2 Fault E&W 231
Hirwaun No 2a Fault E&W 231
Hirwaun No 3 Fault E&W 231
Hudnalls Fault Monmouthshire Mem E&W 233/250

I,J,K

Fault name OS map refCountyBGS map sheetbook references
Itton Fault Monmouthshire Mem E&W 233/250
John Grey's Fault Glamorganshire E&W 247
Keepers Lodge Fault E&W 230
Kilkenny Fault Glamorganshire E&W 231; 249
King's Wood Fault Monmouthshire Mem E&W 233/250
Kinmel Park Fault Denbighshire E&W 95 Mem E&W 95/107

L

Fault name OS map refCountyBGS map sheetbook references
Leeswood Fault E&W 108
Little Mill FaultE&W 232
Llanbadoc Fault Monmouthshire E&W 232; Usk-Cwm:25K
Llancayo Fault Monmouthshire E&W 233 Mem E&W 233/250
Llandrindod - Pen-y-waun Fault Belt E&W 213
Llandyfan Fault E&W 230
Llandynan Fault E&W 121
Llanegryn Fault E&W 149
Llanelidan Fault E&W 121
Llanerchyraur Fault E&W 164
Llanerfyl Fault Powys E&W 150
Llanfabon Fault Glamorganshire E&W 231; 249
Llanfrechfa Fault Monmouthshire E&W 249; Usk-Cwm:25K
Llangattock Fault Mem E&W 233/250
Llanglydwen Fault E&W 210; 211
Llangollen - Llantysilio - Aqueduct Fault Smith et al. 2005
Llangollen Fault E&W 121
Llangwm Fault Monmouthshire Mem E&W 233/250
Llangynidr FaultMem E&W 232
Llanhilleth Fault Glamorganshire E&W 249
Llannefydd Fault Clwyd E&W 107 Mem E&W 95/107
Llanrhaeadr Fault Clwyd E&W 107 Mem E&W 95/107
Llantysilio Fault E&W 121
Llanvair Discoed Fault Monmouthshire Mem E&W 233/250
Llanvair Fault Monmouthshire E&W 250
Llanvapley FaultMem E&W 232
Llanvihangel Fault Monmouthshire Mem E&W 233/250
Llanwonno Fault Glamorganshire E&W 248
Llanwrtyd Fault E&W 196
Llanwrtyd Fault E&W 213
Llechwedd Fault E&W 164
Llethir Fault E&W 230
Llety Wilws Fault E&W 230
Llwyn Celyn Fault E&W 230
Llwyn Fault E&W 165
Llyfnant Fault E&W 163
Llysfaen Fault Denbighshire E&W 95 Mem E&W 95/107
Longoaks Fault Glamorganshire E&W 247
Lunnon Fault Glamorganshire E&W 247

M

Fault name OS map refCountyBGS map sheetbook references
Maen Fault Clwyd Mem E&W 95/107
Maes-gwyn (or Maes Gwyn) Fault Clwyd E&W 107 Mem E&W 95/107
Marian Ffrith (or Marianffrith) Fault Flintshire E&W 95 Mem E&W 95/107
Mathern Fault Monmouthshire Mem E&W 233/250
Mawddach Fault E&W 149
Melai Fault Clwyd Mem E&W 95/107
Brenchley & Rawson 2006
Merthyr Church Fault Glamorganshire E&W 231; 249
Meusydd Fault E&W 230
Minera Fault Belt E&W 121
Minffordd Fault Brenchley & Rawson 2006
Merionethshire E&W 135; 49 Brenchley & Rawson 2006
Moelfre Fault Merionethshire E&W 135
Moel-Gilau Fault Glamorganshire E&W 248
Montgomery Fault Powys Mem E&W 151/165
Morfa Fault Glamorganshire E&W 247, 248
Morlais Fault Glamorganshire E&W 247
Mount Pleasant Fault E&W 230
Mynydd Bach Fault E&W 195
Mynydd Bodrochwyn Fault Clwyd Mem E&W 95/107

N

Fault name OS map refCountyBGS map sheetbook references
Nant Cerrig Fault Clwyd Mem E&W 95/107
Nant Dyar FaultMem E&W 232
Nant Marl Fault E&W 230
Nant y Fedw Fault E&W 196
Nant-Figillt Fault E&W 108
Nantmor Fault Gwynedd E&W 119
Nantygwrdy Fault E&W 164
Nantyricket Fault E&W 164
Nedern Fault Monmouthshire Mem E&W 233/250
Nercwys - Nant-Figillt Fault Zone E&W 108
New House Thrust E&W 165
Newcastle Fault Monmouthshire Mem E&W 233/250
Newlands Thrust Glamorganshire E&W 247, 248
Newmarket Fault Clwyd Mem E&W 95/107
Newton Fault Glamorganshire E&W 247
Newmarket Fault Flintshire E&W 95
Newport Sands Fault E&W 193; 210
Nicholaston Fault Glamorganshire E&W 247

O

Fault name OS map refCountyBGS map sheetbook references
Ochr-y-cefn Fault Clwyd Mem E&W 95/107
Ogof Cadno Fault E&W 193
Ogof Fault E&W 163
Olway Brook Fault Monmouthshire Mem E&W 233/250

P,Q

Fault name OS map refCountyBGS map sheetbook references
Palleg Fault E&W 230
Palmer's Lake Overthrusts Pembrokeshire E&W 244/5
Pant Fault Denbighshire E&W 95 Mem E&W 95/107
Pant-y-fotty Fault Clwyd Mem E&W 95/107
Paper Mill Fault E&W 108
Parc Postyn Fault Clwyd Mem E&W 95/107
Pared Fault Gwynedd E&W 133
Parwyd Fault Gwynedd E&W 133
Pendaren Fault Glamorganshire E&W 249
Penffordd Fault Pembrokeshire E&W 210
Pengam Fault Glamorganshire E&W 249
Pennal Fault E&W 149; 150; 163
Penrhiwfelen Fault Glamorganshire E&W 247
Penterry Fault Monmouthshire Mem E&W 233/250
Pentre Clwydau Fault E&W 231
Pentre Felin Fault Clwyd Mem E&W 95/107
Pentre Llanharan Thrust Glamorganshire E&W 248
Pentremawr Lag Fault Carmarthenshire E&W 229
Pentre Tafarn-y-fedw Fault Clwyd Mem E&W 95/107
Pentwyn Fault (Mons) Monmouthshire E&W 249
Pentwyn Fault (Glams) Glamorganshire E&W 249
Pen-y-castell Fault Glamorganshire E&W 231, 248
Penydarren Fault E&W 231
Pen-y-Fan Fault Monmouthshire E&W 232
Pen-y-llan Fault Monmouthshire E&W 249; Usk-Cwm:25K
Pen-y-parc Fault Monmouthshire E&W 249; Usk-Cwm:25K
Plas Isaf Fault Glamorganshire E&W 247
Pont Morlais Fault E&W 230
Pontarsais Fault E&W 212
Pont-y-ddol Fault Clwyd Mem E&W 95/107
Pontypool Road Fault Monmouthshire E&W 232
Port Eynon Thrust Glamorganshire E&W 246
Portskewett Hill Fault Mem E&W 233/250
Prestatyn Fault Clwyd E&W 95 Mem E&W 95/107
Pwllau Bach Fault E&W 231
Pwllmawr Fault Glamorganshire E&W 247
Pwll-meyric Fault Monmouthshire Mem E&W 233/250

R

Fault name OS map refCountyBGS map sheetbook references
Ramsey Fault Pembrokeshire E&W 209
Rassau FaultMem E&W 232
Reservoir Fault Monmouthshire Mem E&W 233/250
Rhadyr Fault Monmouthshire Usk-Cwm:25K Mem E&W 232
Rhaiadr FaultE&W 137
Rhiw Fault Glamorganshire E&W 249
Rhiw Gwraidd Fault E&W 179
Rhobell Fracture Brenchley & Rawson 2006
Rhos FaultGlamorganshire E&W 231; 232; 249
Rhuallt Fault Flintshire E&W 95 Mem E&W 95/107
Rhydding Fault Glamorganshire E&W 230; 247
Rhyd Sion Wynn Fault Clwyd Mem E&W 95/107
Rhyd-y-creua Fault Clwyd Mem E&W 95/107
Rhymney FaultMem E&W 232
Ritec Fault Pembrokeshire Brenchley & Rawson 2006
Road Uchaf Fault? Brenchley & Rawson 2006
Rock Park Fault E&W 196
Rockfield Fault Monmouthshire Mem E&W 233/250

S

Fault name OS map refCountyBGS map sheetbook references
Sarn-Abersoch Thrust Gwynedd E&W 134
Sawdde Fault E&W 212
Severn Valley Fault Belt E&W 151 Toghill P. 2006
Siamber Wen Fault Denbighshire E&W 95; 107 Mem E&W 95/107
Sirhowy Fault Monmouthshire E&W 232
Six Pit Fault Glamorganshire E&W 247
Soflen Fault Clwyd E&W 107 Mem E&W 95/107
Soughton Fault E&W 108
St Arvans Fault Monmouthshire Mem E&W 233/250
St Brides Fault Monmouthshire Mem E&W 233/250
Stradey Fault Carmarthenshire E&W 229
Strumble Head Fault Pembrokeshire E&W 210
Swansea Fault Glamorganshire E&W 247
Swansea Valley Fault E&W 213
Syddyn Fault Carmarthenshire E&W 229

T

Fault name OS map refCountyBGS map sheetbook references
Tafalog Fault Powys E&W 150
Taipellaf Fault Clwyd Mem E&W 95/107
Talgarth Fault Monmouthshire Mem E&W 233/250
Tal-y-coed Fault Monmouthshire Mem E&W 233/250
Tal-y-llyn Fault E&W 149
Tanant Fault E&W 137
Teifi Fault E&W 212
Tintern Fault Monmouthshire Mem E&W 233/250
Tirdonkin Fault Glamorganshire E&W 247
Tonfannau Fault E&W 149
Trafle Fault Glamorganshire E&W 247
Trawsfynydd - Cwm Bowyd Fault Brenchley & Rawson 2006
Trawsfynydd Fault MW&M:250K, E&W 135
Tredegar Fault Monmouthshire E&W 231; 232
Tre-fal-du Fault Monmouthshire Mem E&W 233/250
Trelleck Common Fault Monmouthshire Mem E&W 233/250
Trelleck Fault Monmouthshire Mem E&W 233/250
Tremadog Thrust Zone Brenchley & Rawson 2006
Tre-'r-ddol Fault E&W 163
Trevethin Fault Glamorganshire, MonmouthshireE&W 232; 249
Trinant Fault Glamorganshire E&W 249
Tumble Fault E&W 230
Tweedle Fault E&W 231
Twrch Fechan Fault E&W 230
Twyn Sych Fault E&W 231
Ty Llwyd Fault E&W 230
Ty Mawr Fault Clwyd Mem E&W 95/107
Tyn-y-caeau Fault (Denb) Denbighshire E&W 95 Mem E&W 95/107
Ty'n-y-caeau Fault (Mons) Monmouthshire E&W 249; Usk-Cwm:25K

U,V

Fault name OS map refCountyBGS map sheetbook references
Upper Artro Fault Merionethshire E&W 135
Usk Fault Monmouthshire Mem E&W 233/250
Denbighshire E&W 121; 95 Mem E&W 95/107
Van Fault E&W 164

W,X,Y,Z

Fault name OS map refCountyBGS map sheetbook references
Warren Fault E&W 230
Smith et al. 2005
UK (south) 625K Brenchley & Rawson 2006
Wenallt Fault E&W 164
Werf Fault E&W 231
West Llangerniew Fault Clwyd E&W 107 Mem E&W 95/107
Weston Madoc Fault E&W 165
Wonastow Fault Monmouthshire Mem E&W 233/250
Wrexham Fault E&W 121
Yspytty Ifan Fault E&W 120
Ystwyth Fault E&W 179 Mem E&W 151/165

List of Disturbances

The following named features comprise both faulting and folding;

table of named disturbances
Disturbance name OS map refCountyBGS map sheetbook references
Caerbryn DisturbanceCarmarthenshireE&W 230
Carreg Cennen DisturbanceCarmarthenshireE&W 230
Clun Forest Disturbance
Cribarth DisturbancePowysE&W 230, 231
Llandyfaelog DisturbanceCarmarthenshireE&W 231
Llannon (or Llanon) DisturbanceCarmarthenshireE&W 230
Neath DisturbanceE&W 231
Pontyclerc DisturbanceCarmarthenshireE&W 230
Saron DisturbanceCarmarthenshireE&W 230
Trimsaran Disturbance

See also

References

Maps

Books