Giant Ginkgo

In on odd twist, a recent topic of thought and conversation of mine has coincidentally become a national story. I've been wondering about the black blobs that are found on sidewalks all over the place. While I am sure that they are generally the result of gum that has been spit out (the local 7-11 has an amazing number of blobs in front of their store), I find it odd that they are all the same black color in all of the locations that I have observed them. (I wouldn't be surprised if the gum heavily attracts automotive pollutants and soot.)

Why do I find them fascinating? Mainly the smooth slightly shiny patina, the blobs don't look like a substance that has been covered with dirt; they look like they started off mixed up that color originally. Plus one rarely sees the transitional state.

On a side note, the black blobs near the 'L' in Chicago are quite often a very noxious oil that drips off of the tracks.