The speaker looks at a logged hillside and sees only devastation. Where a living hill once stood, there is now "raw timber" and "ruins," as if the land were a collapsed building. The first stanza is flat and stunned, almost reporting what the eye takes in.
In the second stanza the feeling becomes stronger. Looking down a "precipice" into "a grave" suggests that the cleared slope is more than damaged scenery. It feels like a death, and the speaker is shaken by it. The word "dreadful" is plain and unguarded, which makes the reaction feel real.
The last stanza turns toward the loggers themselves. They are "full of pillage," a harsh word that casts them as plunderers, and the poem says they turn "some honest joy" into money. The joy seems to belong to the hill, or to simple pleasure in the natural world, now sold off "board on board." The mood is mournful and quietly angry, with no softening at the end.