I am not sure what the Great Carbuncle is here.  In my mind's eye, I just see
a green, very green cemetery at twilight, bathed with a kind of red light
from what is left of the setting sun, a garnet light, darkening into night,
perhaps with a hint of life ending in death, just as evening goes into night.
Bring into that the idea of the meaning of carbuncle as it pertains to infection
and we get a double meaning, perhaps of love ending, becoming almost like
something that is as ugly as the physical carbuncle of infection.  The poem is very
amorphous.  Sue