Verified answer

Yr Wyddfa (Snowdon)

the mountain of Rhobell Fawr

please see link for article

http://www.wales-underground.org.uk/geo.shtml

the mountains of north Wales are the remains of a huge volcanic plateau and there are volcanic rocks distributed throughout the British Isles. Even in the Chalk of Southern England, many of the thin marl seams (eg. Newhaven Member) are now considered to be volcanic ash deposits. Volcanoes have therefore played a significant part in the geological history of the UK. None of the volcanoes will become active again in the foreseeable geological future.

Volcanoes - North Wales and South Mayo - Rhobell Fawr 510 ma

Volcanoes - North Wales and Lake District - Borrowdale - Helvellyn &

Scafell Pike

Hope that helps

the conwy

http://www.bbc.co.uk/wales/northwest/sites/nature/...

I do, I've answered your previous question!