Milton Wilson notes that another influence on Shelley while he was describing the Ionian isle is the convention of the pastoral, "which, for Shelley, was exemplified not merely by the classical ecologues or pastoral elegies, but in the English by A Midsummer Night's Dream, The Winter's Tale, The Tempest, The Faithful Shepherdess, The Sad Shepherd, and most of the early poems of Milton. This convention, whatever sensuous suggestions may allow, demands that the images be judiciously generalized, or, at least, achieve a balance between numbering the streaks of the tulip and sketching a remote panorama" (114). These remarks are based on Wilson's commentary of lines 530-35 and 541-48. The many texts that Shelley may have relied on while constructing this scene reminds us of his voracious reading, which, as is the case with Keats, contributed to a poetical style that was more literary than Wordsworth, who was much more concerned with his personal interaction with nature.
Wilson, Milton Thomas. Shelley's Later Poetry. New York: Columbia UP, 1957.