It looks as though the song was written around a well-known joke that was circulating even before the Civil War:

Official Proceedings St. Louis Railway Club, Feb. 14, 1902:

"You remember that Noah built himself a ship with the pleasant expectation of being the only man that would be afloat when the flood came, and the time came when the heavens opened and the rain fell, and Noah was afloat; and as usual with those who have the happy instinct of being able to get ready for'I told you so,' he looked out of the window one day and saw a gentleman swimming around ther, hanging on to a piece of stick, and the man says to him, 'Let me in.' 'Oh, no,' says Noah, 'I can't do that,' and the man says, 'Go on with your darned old scow, it is only a rain storm anyhow.' (Laughter.)"


Minnesota Pioneer (St. Paul), May 17, 1852:

"Although the treaty is our ark ofpromise and of hope, still if the Senate *will* close it up, we can say as the poor fellow said to old Noah, 'be off with your old scow; there will be only a sprinkle of a shower, any how.'"

Same, March 30, 1854:


“We recollect to have heard a story of a loafer in the days of Noah, who, after the rain had endured for some time, and the waters began to ‘spread themselves,’ made out to wade to the ark, and was very solicitous for a passage. Noah told him that the thing was impossible, the ark was fully freighted, and being closed, nothing more could be taken on board. The loafer became very urgent and insisted that as no other vessel would be putting out in the same direction for some time, and as the waters were entirely covering the land, so that the lives of those on shore were endangered, it was the duty of the ‘Captain’ to assist and save his fellow beings. All the arguments of the loafer, however, proved of no avail, and when he had satisfied himself that there was no chance whatever of obtaining a passage, and becoming convinced that if he remained much longer where he was, he would run a great risk of drowning, he turned from th uncouth craft, and giving it a kick, told Noah that he might go to the devil with his old scow, for he would not disgrace himself by traveling in it, - and from appearances, he did not believe there would be much of a shower any how.”

(Sour grapes plus wishful thinking.)