Motif of disease/decay
It is connected to the Devil's Acre loop. It is a decaying rotting place with muddy decaying houses, filthy river that is used as a drain and spring. It is a mirror of the corruption of the people that live there. It also foreshadows the upcoming trouble that the peculiar heroes will face.
Library of Souls allegory
Library of souls is an allegory for knowledge, or the misuse of knowledge. The souls of peculiars are passed on from generation to generation the same way the knowledge gets past on. Controlling peculiar souls means having power the same way having knowledge means having power. It is the misuse of that power that is troubling.
Names of places symbolism
It is again connected to the Devil's Acre loop. The name itself gives out the contents of the loop; it is reminiscent of Hell, the devil in this case being Caul who is controlling this acre. There are also names like Fever Ditch and Capital of Cholera- self explanatory referring to a diseased place. The names of places aren't always giving out the state of places, like Periwinkle Street and Oozing Street which are opposite from what their names tell but, instead of taking away from, this only adds to the confusion and the wrongness.
Mother Dust symbol
Mother Dust symbolizes sacrifice on a quite literally. She is turning to dust while helping others; she is literally disappearing when she helps other, which brings sacrifice to a whole new level. While in everyday life sacrifice takes a toll on a person emotionally and physically, here it is visually demonstrated which makes one think.
Motif of death
Motif of death is ever-present in the Devil's Acre, death is not a big deal here, and it is a part of the everyday life.
"He opened the door and swept us out into the dying day."