This passage has a melancholic mood. You can tell this due to some specific key words: "dull", "dark", "soundless." They all have a negative connotation. The imagery of a lone rider in a dreary and dull country under the oppressive sky may clue you in that the overall passage has a sad tone to it. Even later in the passage the author states that the scene is melancholic.
Synecdoche - <span>They drive their keels o'er the darkling wave</span>
Alliteration - Grim and greedy, he grasped
Kenning - The whale-path
Epithet - The Ruler-of-Man
They can be depending on use
