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The existence of such a map would certainly seem possible. Orcadian
tradition maintains that sailors/explorers from Orkney visited North
America in the early 1400's, and indeed the chapel at Roslyn just
south of Edinburgh built by the Earls of Orkney around 1440 includes,
amongst other things, depictions of maize cobs in the stone carvings.
 
You would need to confirm this with an expert on Orkney and Norse
history as I am going by memory from the guide book for Roslyn
Chapel.
 
regards,
 
Tim Rideout
Bartholomew