Complex sentence: Slate quarrying was once big business in the Preseli Hills and remnants of the quarries can still be seen in Rosebush, Pembrokeshire and there is a slate workshop today still at Llangolman where authentic Welsh slate is still used in a variety of craft items.
Split into simpler sentences: Slate quarrying was once big business in the Preseli Hills, and remnants of the quarries can still be seen in Rosebush, Pembrokeshire. There is still a slate workshop at Llangolman where authentic Welsh slate is still used in a variety of craft items.