The poem is very short, but it sets up a strange, vivid contrast. In the first two lines, the speaker describes the dirt as a ship that has been lost beneath the frost. The title, "Landlubbers," is a word for people who know land rather than the sea, so the joke is that these are sailors who have never really left the ground. The ship is buried, stuck, and hidden under ice.
The second stanza turns from the ground to the speaker's own body. Out in the cold, the speaker begins to "burn all over." That could mean a physical reaction, since extreme cold can sting like heat, or it could be a rush of feeling, such as longing, anger, or excitement. The poem doesn't say which, and that openness is part of its charm.
The mood is quiet, odd, and a little startling. The cold and the burning pull against each other, leaving a sense of something alive and restless under a frozen surface.