Modifies a noun

• abyss: Victorian thinkers called it the ' great chasm ' or the ' fathomless abyss ' .

• depth: Soundtrack to your most vivid nightmare, the song's fathomless depths seem to hold infinite nameless creatures of the night.

• mystery: Far be it from His glory that human tongue should adequately recount His praise, or that human heart comprehend His fathomless mystery.

• blue: Two tones of blue, presumably depicting the fathomless blue of air [ a reference to the books title?

• eye: It was staring at him with fathomless black eyes, its sharp curved beak almost smiling.