The singer recalls St Patrick's miracles while the liquor holds out: he arrived mounted on "a paving stone," drank a gallon of liquor from a quart pot, turned mutton to salmon on Friday, and drove out the snakes.
Croker-PopularSongs discusses the miracles in some detail. Apparently, it was not Patrick himself but a leprous disciple -- refused passage on Patrick's ship by the crew -- who accompanied the ship on Patrick's stone altar thrown into the sea as a float for the purpose. Patrick, at one point, craves meat on Friday but an apparition has Patrick put the meat into water; when the meat turned into fishes Patrick was saved by the miraculous sign from sinning and never ate meat again. Dr Maginn's source for the "facetious" [Croker's term] song is Father Jocelyn who, Croker points out, did not mention the "miracle of the Saint's 'never-emptying can, commonly called St Patrick's pot'." In the last verse the singer wishes that he had such a pot so that he could continue the song. - BS
According to Benet's _Reader's Encyclopedia_, Dr. William Maginn (1793-1842) was the "Prototype of Captain Shandon in _Pendennis_ by Thackeray." _The New Century Handbook of English Literature_ lists him as the co-founder of _Fraser's Magazine_, and mentions among his works _The City of Demons_ and _Bob Burke's Duel with Ensign Bray_. His most popular poem was probably "I Give My Soldier Boy a Blade," though I find myself more intrigued by the title "the Rime of the Auncient Waggonere." - RBW