While in Los Angeles sidewalk gum is black, on the sidewalks of England it is always white, often looking like silvery British coins. Indeed, I found several five pence coins camouflaged within this unique habitat.

I suspect that the reason sidewalk gum is white in England and black in other places is because of the prevailing climate of clammy cold, which quickly renders abandoned gum into a hard, non-sticky mass. In Los Angeles (or Lawrence, Kansas) on the other hand, abandoned gum often finds itself on broiling hot concrete or asphalt, where its stickiness is maintained long enough for it to be completely covered with black sidewalk grime.