What is an example of tone in Frankenstein?

Oh! No mortal could support the horror of that countenance. A mummy again endued with animation could not be so hideous as that wretch. I had gazed on him while unfinished; he was ugly then; but when those muscles and joints were rendered capable of motion, it became a thing such as even Dante could not have conceived."

This example indicates a dark, horrific, tone which is pervasive in the novel.