I was wandering through an infiltration website (exploring old properties, tunnels, abandoned buildings) and I came across this picture. I'm not a huge geology buff, so maybe someone can tell me what layer of the geological column this is:

The image, it appears, is very grainy on blogspot, but those are cars in the embankment. Reminds me of the time I found a 1930's Dr. Pepper bottle in supposedly a fifty million year-old fossil bed. I'll have to see if I can clean that image up somehow.

By the way, this interest in infiltration has been spurred on by some research I'm doing for my current novel, and the fact that I now have my own digital camera with which to take pictures.