Sling or Ellwood nr Coleford would be my best guess to help explain where "Marsh Lane" area is.

If you try Multimap or Google Maps , then use the post code >>> GL16 7NA

Or if you want to see the Marsh Lane area in the late 1800's try

http://www.old-maps.co.uk/
co ords 358752,207857

where you can get a modern OS map tile , and an aerial view.