Time in a Bottle

I haven't had the luck of finding a fully intact old bottle, but I keep my eye out. I suppose an old Coke bottle doesn't count (I'm not even sure how old this is - 2 years maybe).
Anyhow, bottle dating can be useful in determining the possible age of an old fenceline or monument when you are working far from civilization - problem is you have to find the bottle first and then be able to date it. Just a possibility I guess, but one worth considering enough that the BLM has their own web page dedicated to the subject. This is an interesting link to the BLM archeology site concerning hisoric bottles.