Note on country lacking northern coastline? (8)
I believe the answer is:
tidemark
'lacking northern coastline?' is the definition.
'tidemark' can be an answer for 'coastline?' (line or mark left by the sea on the shore). I am not certain of the 'lacking northern' bit.
'note on country' is the wordplay.
'note' becomes 'ti' (musical note as in do re mi so fa la ti).
'on country' becomes 'demark' (I can't justify this - if you can you should give a lot more credence to this answer).
'ti'+'demark'='TIDEMARK'
(Other definitions for tidemark that I've seen before include "Line on shore" , "line on beach" , "shows extent of clean-up" , "Indication of filthy washer" , "Dirty line in a bath" .)