Its a bloomin' long time underground for anything of worth to have survived... having said that.. bear with me here... I started a compost heap (well a lazy pile of garden crap, newspaper and card) about 10-11 years ago. I didn't follow any of the guidelines on watering it and turning it, just piled it up.
Anyway about a fortnight ago I decided that due to a shed requirement to create storage space which will eventually clear a room to give me a new large collecting room... I said to bear with me... anyway I needed to clear the old heap.
The top half was dry and went in sacks to the tip, the next layer reasonably rotted and made its way into my veg beds, the bottom layer though that was at the time layered with cardboard and the oldest part of the heap had all sorts of definable stuff... egg shells, melon skins, newspaper with print still legible and cardboard boxes/sheets (the laminated print from lolly packaging for example (similar to a card-back I guess) were most notably recognisable as well as other boxes with some structure to them.
It can't be beyond belief that under 40ft of back fill a few pieces may well be worth picking out even in our climate. Certainly an interesting dream that will capture more than just our imagination I'm sure!