The most easily recognisable evidence of iron smelting at Blayshaw is a slag heap which in its size and in the nature of its contents is typically medieval. It is highly likely to be a remnant of industrial activity by Byland Abbey.
The fence in the photograph passes over the heap.
The slag came from bloomery furnaces nearby
Slag at Blayshaw
Slag is the residue that is left after smelting, essentially the solidified molten rock from the ore and carbon from the charcoal.