Slater's labourer?
Two possibilities I suspect:
1. Working at a stone works helping in the manufacture of stone slates using the beautiful stone in the area that was used for both walls and roofs, generally moving uncut stone blocks around, sorting and stacking the stone slates by size ready for sale to roofers. Heavy labouring work.
2. The more likely job was working with a roofer installing the stone slate roofs. He'd probably either help unload stone slates from a supplier or help the roofer/slater split stone blocks to make their own slates, 'drill' the oak peg or wrought iron nail holes in the stone slates and carry them up to roof level together with the timber battens, making the lime mortar for the pointing and carrying that up to roof level and possibly the lead sheeting for the flashings. A hard labour job that's for sure involving lots of ladder work.