This EarthCache is placed with the kind permission of the National Trust, for which they are gratefully thanked.
Under no circumstances are any of the rocks or vegetation on the mountain, or its neighbouring hills, to be either disturbed or removed. Please leave the mountain as you found it and so allow others to also enjoy this magnificent area.
The geological foundations of the Brecon Beacons National Park are of global significance. In October 2005, the western half of the National Park was accepted into the prestigious European and Global Geoparks Network as ‘Fforest Fawr Geopark’. The Brecon Beacons remains the only British National Park to encompass a Geopark. The rocks here range from Ordovician, through to Carboniferous, with a smattering of Quaternary deposits overlying these.
Two thirds of the area of the Park is comprised of Old Red Sandstone rocks, forming four distinct blocks of hills which are cut through by major river valleys. One of these, the Central Beacons, is the range of hills to the south of Brecon. Rising from this range is Pen Y Fan, the highest peak in the Park and the highest in Britain south of Snowdonia, rising to a height of 886m above sea level.
Pen Y Fan is formed from layer upon layer of ‘Old Red Sandstone’, a thick sequence of sandstones, mudstones and siltstones often referred to familiarly by geologists as 'the ORS'. The near-flat triangular summit plateau of Pen Y Fan, like that of its similar, but slightly lower, near neighbour Corn Du, is formed from the relatively erosion-resistant sandstones of the ‘Plateau Beds’. These rocks date from around 370 million years ago, and are part of a thin late Devonian sequence which between them constitute the Upper Old Red Sandstone and which overlie a much thicker Lower Devonian-aged 'Brownstone' and 'Senni Beds' of the Lower Old Red Sandstone.
To claim this EarthCache, please study the iconic flat summit plateau of Pen Y Fan, then answer these questions:
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What colour are the rocks?
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What features can be seen across all of the exposed in-situ surfaces within the Plateau Beds?
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Are the rocks sedimentary, igneous, or metamorphic?
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Given your above observations and deductions, do you think these rocks were laid in:
a hot, windy, dry, desert environment, where massive sand dunes piled up on top of each other
or
a vast delta, where rivers periodically washed over older surfaces, possibly over flat sandbanks?
TO CLAIM THIS EARTHCACHE - As usual with EarthCaches there is no physical cache. Please email or message me the answers to the above questions. Once you have emailed me your answers, please feel free to log your find. Any dubious or incorrect answers I will contact you about, and possibly delete if way off. Why not also have a photo taken at the National Trust Plaque at the summit and upload it with your Log. Please do not add any spoiler photographs of the Plateau Beds themselves.
Good luck! 