Time, Real and Imaginary (unsourced)

ON the wide level of a mountain's head (I knew not where, but 'twas some faery place), Their pinions, ostrich-like, for sails outspread, Two lovely children run an endless race, A sister and a brother! This far outstripp'd the other; Yet ever runs she with reverted face, And looks and listens for the boy behind: For he, alas! is blind! O'er rough and smooth with even step he pass'd, And knows not whether he be first or last.