Since Roman times, the quality of Welsh slate has made it a premier building material, with top architects still demanding it for prestige projects. This makes it a candidate for "Global Heritage Stone Resource" status. North West Wales is recognised as the region producing the best product. It occurs in two strips that straddle a line running through the Llyn Peninsula. The original sediments in the Bethesda-Nantlle Belt are Cambrian in age - a little over 500 million years old; the Blaenau Ffestiniog belt is slightly younger (Ordovician). Both experienced their metamorphism during tectonic events in the Silurian Period, about 400 million years ago. Read more
The slate deposits of Wales belong to three geological series: Cambrian, Ordovician and Silurian. The Cambrian deposits run south-west from Conwy to near Criccieth; these deposits were quarried in the Penrhyn and Dinorwig quarries and in the Nantlle Valley. There are smaller outcrops elsewhere, for example on Anglesey. The Ordovician deposits run south-west from Betws-y-Coed to Porthmadog; these were the deposits mined at Blaenau Ffestiniog. There is another band of Ordovician slate further south, running from Llangynnog to Aberdyfi, quarried mainly in the Corris area, with a few outcrops in south-west Wales, notably Pembrokeshire. The Silurian deposits are mainly further east in the Dee valley and around Machynlleth. Read more