and the slow fires trailing from the abandoned camp-sites, (13-14)
Dark imagery sets up this scene. We can imagine smoke pluming in the distance signifying an ending or loss. A crucial word in this passage, "abandoned," means that these places were completely deserted. Perhaps the speaker still relates to these "camp-sites" in some way despite leaving them behind. Or, maybe he misses his old pals who used to occupy those places, but are no longer with us.
over which scavenger angels wheel on heavy wings. (15-16)
Scavengers feed on the dead and angels, well, we usually don't see them when we're alive. So these lines indicate that some sort of death has taken place. On the other hand, it's intriguing that the speaker himself not only sees the scavenger angels but also seems to be in cahoots with them.
the manic dust of my friends, those who fell along the way, bitterly stings my face. (23-25)
The speaker's caught up in memories of his friends who have fallen by the wayside, but it's not clear if they have literally or metaphorically died. Since "The Layers" is a conscious exploration of life, it might not matter if his friends physically died, only that they're no longer growing or "changing" like the speaker is.