The line 'It was late last night when ------ came home' derives from American versions of Child 200, The Gypsy Laddie. American versions go under such titles as 'BlackJack Davy', 'Gypsy Davy'.

'Till the seas run dry
Till the rocks melt in the sun' is a universal commonplace, part of a large family of stanzas sometimes known as 'impossibilities', used to denote when something will never happen. Or in the above case to show eternal love.

Other lines are borrowed from earlier American songs. There is a strong and early tradition, in the English-speaking world, of forming medleys from snatches of different songs, which may be similar to what has happened here.