The story/novella is a kind of detective story, with a doctor as a narrator, and there are lots of dialogue and inductive reasoning, so Poe keeps the figures of speech to a minimum.
He uses colloquial dialogue (Black English):
"Dey aint no tin in him, Massa Will, I keep a tellin' on you," here interrupted Jupiter;
"this is a very passable skull -- indeed, I may say that it is a very excellent skull, according to the vulgar notions about such specimens of physiology
Rhetorical question and imagery (in bold):
Do you observe how mere an accident it was that these events should have occurred upon the sole day of the year in which it has been, or may be sufficiently cool for fire, and that without the fire, or without the intervention of the dog at the precise moment at which he appeared, I should never have become aware of the death's head, and so never the possessor of the treasure?
I had put together two links of a great chain. There was a boat lying upon the sea-coast, and not far from the boat was a parchment -- not a paper -- with a skull depicted on it.