Lyell in his book about America, says that the Falls of Niagara, if (as seems certain) they have worked their way back southwards for seven miles, must have taken over 35,000 years to do so at the rate of something over a foot a year! Sometimes they fall back on a stratum that crumbles away from behind them more easily: but then again they have to roll over rock that yields to them scarce more perceptibly than the anvil to the serpent. And these very soft strata, which the Cataract now erodes, contain evidences of a race of animals, and of the action of seas washing over them, long before Niagara came to have a distinct current; and the rocks were compounded ages and ages before those strata! So that, as Lyell says, the geologist, looking at Niagara forgets even the roar of its waters in the contemplation of the awful processes of time that it suggests. It is not only that the vision of Time must wither the Poet's hope of immortality, but it is in itself more wonderful than all the conceptions of Dante and Milton. This train of thought was evidently often present to FitzGerald's mind. It oppressed him. It makes itself felt in the _Rubáiyát_. It was one of the many great ideas he imported into, or educed from, the old Persian Astronomer. And fear not lest existence closing your Account, and mine, should know the like no more; The Eternal Saki from that Bowl has poured Millions of Bubbles like us and will pour When you and I behind the Veil are past: Oh but the long long while the world shall last, Which of our coming and departure heeds As the Sev'n Seas should heed a pebble-cast. It was even more constantly present to the mind of Tennyson. Astronomy and Geology had been among his favourite studies from his early youth, and remained so all his life. When I was walking with him toward the Needles and looking at the magnificent chalk cliff below the downs, and spoke about his felicitous epithet for it--"the milky steep," he said, "The most wonderful thing about that cliff is to think it was all once alive." The allusions to it in his poems are innumerable: There rolls the deep where grew the tree, O earth, what changes hast thou seen! There where the long street roars, hath been The stillness of the central sea. He was always "hearing the roll of the ages." He, too, had read his Lyell, and the contemplation of geological time suggested to him exactly the same reflections which FitzGerald draws out. Indeed, it seems not unlikely that he himself may have imparted them to FitzGerald. For he has embodied just these thoughts in that noble late poem "Parnassus," with a resemblance which is startling. But while the parallel between "Parnassus" and FitzGerald's letter is extraordinarily close up to a certain point, the contrast, when it is reached, is even more striking, and is the fundamental contrast between the two men and their creeds: