Hay Bluff overlooks the beautiful town of Hay on Wye, which is world famous for its wealth of bookshops. Just a short drive from the town down a winding country road takes you to the northern most tip of the black mountains where you are greeted by the peak of hay bluff. Hay Bluff is 677m in height and boasts excellent views of the surrounding area on a clear day. The mountain is a very popular place for families, hikers of all levels and Hang gliders. Once at the top of the mountain you can follow the Offa’s dyke trail which follows the England/Wales border for 177 miles.
While walking along it is hard to ignore the large outcrops of rock that stick out of the landscape. While walking along I noticed and looked at 3 large outcrops, from this I identified 2 different sedimentary units, the first was a coarse grained sandstone unit. This is typical of the old red sandstone which dates back to the lower Devonian around 400 million years ago. At this time the first terrestrial rocks were being deposited over Herefordshire and the surrounding area. This was due to the world’s continents colliding with each other which went on to form the supercontinent Pangea. Looking on geological maps the sandstone looks to belong to the Senni Formation which is characterised by green coarse grained sandstone and is believed to have been deposited in fluvial channels.
The second sedimentary unit was a matrix supported conglomerate which underlay the sandstone. The clasts were on average 3-5cm wide and were well rounded. The matrix looked to compose of fine sand which ‘glued’ the clasts together. This unit is also dated at just over 400 million years old, at the start of the Devonian. This unit outcrops over a larger area than the previous unit and I think relates to the St Maughans formation which is characterised by many rock types not just conglomerate. The formation is believed to have been deposited in a braided river system on flat open land.
References:
http://79.170.44.138/earthheritagetrust.org/pub/learning-discovery/aggregates/lithology-profiles/senni-formation/
http://www.blackmountainsite.co.uk/other-places-to-visit/peaks/hay-bluff/
http://maps.bgs.ac.uk/geologyviewer_google/googleviewer.html
http://79.170.44.138/earthheritagetrust.org/pub/learning-
discovery/aggregates/lithology-profiles/st-maughans-formation-ditton-group/
http://www.offasdyke.demon.co.uk/
