Every time I sing this with a group, there is a "discussion" of whether it's 15 MILES or 15 YEARS on the Erie Canal. I have looked into all my songbooks & sourcebooks, and can find no agreement (as there is none here). Most versions say MILES. However, I have seen a very old copy of the sheet music on display in one of the history kiosks along the New York Thruway, I think at Chittenango, and it says YEARS. In his book BODY, BOOTS AND BRITCHES Harold Thompson, eminent folklorist of eras past, says: "...when Mr. Thomas S. Allen published it in 1913, we were already in sight of the day when the Barge [canal] was to replace the Erie--the Barge which has no towpath for Sal...here is part of Mr. Allen's ballad as originally published: '...Fifteen years on the Erie Canal.'" With those two sources close to the source, I always insist on YEARS, because Sal is his good ol' pal for such a long time, and it's her love-song. MILES probably means the usual shift of one mule before giving him/her a rest and possibly changing to the other mule on board. (Though who could rival Sal??)