Line of stitches (4)
I believe the answer is:
seam
'line of stitches' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for seam that I've seen before include "Join - stratum of ore" , "Underground layer of mineral" , "A layer of coal in ground" , "Join - thin layer" , "A stitched join in a garment" .)