| Quote #1
The imagination of the observer clung by preference to that vanished, solitary figure, as to something more interesting, more important, more likely to have a history worth knowing than these new-comers, and unconsciously regarded them as intruders. (1.2.46)
Diggory thinks this about Eustacia, but the novel as a whole seems to believe it too – the idea that the "solitary figure" has a more interesting story than the community. And this book definitely focuses on a series of solitary figures (though it doesn't ignore the community and human connections). This idea of a "solitary figure" is a very Romantic idea as well; Naturalist thinking is more likely to describe an isolated figure, which has a more negative connotation, or meaning.
| Quote #2
That five minutes of overhearing furnished Eustacia with visions enough to fill the whole blank afternoon. [...] She could never have believed in the morning that her colourless inner world would before night become as animated as water under a microscope, and that without the arrival of a single visitor. (2.9.29)
We get a very strong sense of how isolated Eustacia is, and of how much she lives inside her own head. The mention of the microscope is also unusual; this book doesn't otherwise use many scientific or technological comparisons. This might just be a random comparison, but it draws attention to how little technology of any sort features in the novel.
| Quote #3
Yeobright reached the empty house about mid-day. It was almost as lonely as that of Eustacia's grandfather, but the fact that it stood near a heath was disguised by a belt of firs which almost encircled the premises. (3.6.6)
The detail about the trees "disguising" the heath is significant here. When they first arrive at their new home, Clym and Eustacia live in a fantasy land that's practically a bubble, and Eustacia ignores the fact that they still live on the heath in favor of dreaming about Paris.