Old B&M timetables show there used to be a junction at North Berwick where a line from Portsmouth connected to the existing line from Dover. Where was that junction? I haven't spotted any trace of it during on any of my recent Downeaster trips.
As late as 1944 the line up from Portsmouth to North Berwick is shown on topo maps of time.
Basically came in along what is now Eastern Ave joined the main at Main Street. Power line running SSW of N Berwick
is where the ROW was toward Agamenticus and then Jewett. At Agamenticus, there was another branch back to South Berwick.