Definition of "spangling"

It was a crumbling heap, whose portal dark / With blooming ivy trails was overgrown; / Upon whose floor the spangling sands were strown, / And rarest sea-shells, which the eternal flood, / Slave to the mother of the months, had thrown / Within the walls of that gray tower, […]

1817 December, Percy Bysshe Shelley, “The Revolt of Islam. […]”, in [Mary] Shelley, editor, The Poetical Works of Percy Bysshe Shelley. […], volume I, London: Edward Moxon […], published 1839, page 220