Haydn's "New Created World" (The Creation)
Franz Joseph Haydn (1732-1809) composed his oratorio, The Creation, late in his career, between 1796 and 1798. The libretto, originally in English, is based on the biblical story and on Milton's Paradise Lost; it was translated into German by Baron Gottfried van Swieten. Haydn's Creation was first performed in 1798, but it had its London première in 1800, in Covent Garden Theatre. The archangels, a chorus, and Adam and Eve make up the singing parts, and these were in the eighteenth and nineteenth centuries usually accompanied by a very large orchestra.
Mary Shelley's friend Vincent Novello, who was serving as chapel organist at the Portuguese Embassy at the time, arranged a vocal score with separate accompaniment for organ or piano in the 1820s--two excerpts of which, from a twentieth-century reprint, are included here:  the portion played in the sound clips below; and  the portion probably alluded to in the novel (III.7).
This is among the many works he played for Mary Shelley in 1823. Jean de Palacio and others have suggested, based on Shelley's letters from this period, that Novello's music--particularly his playing of the Creation--inspired her composition of The Last Man as a whole. Music is closely connected to imaginative creation in this novel of apocalyptic uncreation, and Shelley explicitly refers to the Haydn (which, significantly, is played on the organ) in one crucial scene (III.7).
Here are two versions of a digital sample produced from Novello's score (number  above):