Stitched line (6)
'stitched line' 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 - thin layer" , "Fabric joint" , "Sewing join" , "Stratum (of a mineral)" , "Unfasten" .)
(Other definitions for yonder that I've seen before include "Over there, a long time ago" , "Over there, somewhat archaic" , "Over there, of old." , "In that direction" , "Distant but within sight" .)