There's a railway connection here isn't there :-)
It's a rail wagon innit :)
There is a railway line not too far away, but that's true of a large number of the Welsh slate quarries.
Edit: There is a railway station a little over 2km away as the crow flies, but I very much doubt that this particular railway ever served the quarry in question. There is a completely different railway, at a different gauge, approximately 3km away as the crow flies.