From "Sailor Songs," by William L. Alden (Harper's new monthly magazine. / Volume 65, Issue 386, July 1882, p. 283):

One of the best known of the windlass songs was the "Shanandore":

SOLO. Andante.
You Shanandore, I long to hear you.
CHORUS.
Hurrah, you rollin' river!
SOLO.
You Shanandore, I long to hear you.
CHORUS.
Ah, ha, you Shanandore.

This is clearly of negro origin, for the "Shanandore" is evidently the river Shenandoah. In course of time some shantyman of limited geographical knowledge, not comprehending that the "Shanandore" was a river, but conceiving that the first chorus required explanation, changed the second chorus. Thus the modified song soon lost all trace of the Shenandoah River, and assumed the following form, in which it was known to the last generation of sailors:

SOLO. Andante.
For seven long years I courted Sally.
CHORUS.
Hurrah, you rollin' river!
SOLO.
I courted Sally down in yon valley.
CHORUS.
Ah, ha! I'm bound away on the wild Missouri.