Mary Shelley quotes from Byron's Childe Harold's Pilgrimage, Canto III, stanza 62, written the same summer, 1816, in which she began Frankenstein.
. . . Above me are the Alps,
The palaces of Nature, whose vast walls,
Have pinnacled in clouds their snowy scalps,
And throned Eternity in icy halls
Of cold sublimity, where forms and falls
The avalanche—the thunderbolt of snow!
All that expands the spirit, yet appals,
Gather around these summits, as to show
How Earth may pierce to Heaven, yet leave vain man below.