Tone in The Chambered Nautilus

In this case, the noun “main” refers to the sea. This definition of “main” is a truncation of “the main sea,” meaning “the powerful sea.” To call the sea “unshadowed” is a tonal flourish, intended to evoke the fanciful vision of the sea that prevails over the course of the poem. In reality, the chambered nautilus is a frequent denizen of the marine layer known as the dysphotic—or “twilight”—zone, ranging down to depths of 1,000 feet where sunlight barely penetrates.