Underground line
I believe the answer is:
seam
(Other definitions for seam that I've seen before include "Line of join" , "Underground layer of mineral" , "Fabric joint" , "A layer of coal in ground" , "Stitched joint" .)
I believe the answer is:
seam
(Other definitions for seam that I've seen before include "Line of join" , "Underground layer of mineral" , "Fabric joint" , "A layer of coal in ground" , "Stitched joint" .)