Given how many different genres this book has working together, it's not surprising that we have a lot of different tones here too. Layers of tone, like a complex musical piece. First up, we have the distant and philosophical tones, which are basically a brainy sort of distance from the action. The narrator frequently analyzes events and people, and especially the landscape, without getting emotionally involved in it. There's very little sympathizing here; instead, there's a lot of intellectual pondering, which often happens through a bunch of allusions. And the narrator isn't the only one who's philosophical and fond of observing things in a fairly detached way. Just check out this dialogue from Eustacia:
"No. Only I dread to think of anything beyond the present. What is, we know. We are together now, and it is unknown how long we shall be so." (3.4.66)
If she had launched into some "To be, or not to be" there, we wouldn't be surprised at all. But this isn't to say that the entire novel is filled with deep thoughts and intellectual ideas. We also have a lot of romance, and the tone of the novel definitely reflects that. But even the romantic comparisons can't escape the philosophical tendencies, or the humor (yes, humor) that's present in the novel.
They were like those double stars which revolve round and round each other, and from a distance appear to be one. The absolute solitude in which they lived intensified their reciprocal thoughts; yet some might have said that it had the disadvantage of consuming their mutual affections at a fearfully prodigal rate. (4.1.2)
We start out with a very romantic description of stars orbiting one another, but the tone shifts in the back half of this section. We get a reference to "some might have said," which is always a good sign of philosophy at work; the all-knowing "some" or "one" say so. And we end with a display of rather snarky British humor, with the reference to a "fearfully prodigal rate." It's a snooty way of saying that Eustacia and Clym's summer romance won't last.
It's the wit and humor of the novel that's really worth noting here. Word choices, little throw-away lines, and snarky asides from the narrator and other characters can really catch you off guard in this largely serious novel. But it's these little displays of humor in the tone that keep the novel from becoming too overbearing and depressing. Check out this paragraph, which starts off with a melodramatic tone and ends with some snark:
The wings of her soul were broken by the cruel obstructiveness of all about her [...] She uttered words aloud. When a woman in such a situation [...] takes upon herself to sob and soliloquize aloud there is something grievous in the matter. (5.7.19)
The narrator is kind of making fun of a super distraught Eustacia here. But this display of humor isn't totally out of place. The humor also feeds into the distance and intellectual-bent of the tone. Humor here has a distancing effect and helps the novel as a whole shy away from sentimentality.