Well, I was so excited when I first looked at this thread, because I was thinking that a friend had told me some time ago that plastic does exist naturally in the earth. After looking it up, I found that the friend had said polymers, not plastic. What is the difference, please?

Oh, and for the record, the clay that lies underneath our thin layer of topsoil is indeed greasy and nasty-looking, as I discovered one year whilst digging the tomato patch.

EDIT: I got to wondering where the word patch came from, and the best I could come up with is that nobody knows. A couple of dictionaries said it may have come from the French word for piece; another said maybe Old Italian. Ultralingua had the most detail, but offered yet another source: [ETYM: Old Eng. pacche; of uncertain origin, perh. for placche; cf. Prov. Eng. platch patch, LG. plakk, plakke.]