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W

• Welsh Borderland Fault System / System Ffawtio'r Gororau

Set of faults trending NE-SW through Shropshire and into mid and South Wales. It comprises the Church Stretton Fault Zone which extends south-westwards through the Geopark as the Carreg Cennen Fault, the Tywi Lineament and the Pontesford Lineament. It may be a terrane boundary.

• Wenlock Series or Wenlockian / Cyfres Gweunllwg

Stage of the Lower Silurian. See Silurian timechart.

• Westphalian / Westffalaidd

Stage (subdivision) of the Carboniferous period. See Carboniferous timechart.

• Windermere Stadial / Rhyng-gyfnod Cynhesol Windermere

Subdivision of the late Pleistocene epoch between about 15,000 and 13,000 years ago during which Wales enjoyed a temperate climate.

• Wrekin Terrane / Tiriogaeth grammenol Dinlle Gwrygon 

A terrane is a section of the Earth's crust, the rocks of which share a common geological history. Terranes are bounded by major strike-slip faults. The Wrekin Terrane is a roughly triangular area whose corners are at Tenby, Stoke-on-Trent and Bristol.  It is defined by the 'Malvern Lineament' in the east, the 'Variscan Front' in the south and the 'Welsh Borderland Fault System' (see above) in the north-west. Most of Fforest Fawr Geopark lies within these boundaries.

• Wye Glacier / Rhewlif Gwy

A broad glacier or river of ice which flowed down the valley of the present-day River Wye during one or more of the ice ages.

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