[Drammach]

According to the National Geographic article I linked above, the river's bed is a very fine grain sediment that preserves the artifacts..
I would guess it is much like the peat bog mummies, etc., in that the items are protected from oxygen, therefore rust, oxidation does not occur...
Apparently this works well with not only metals but wood, fibers, etc..

[potlatch]

Thank you Drammach. I read the top of the thread but didn't go to the link as you well know. Lack of oxygen and the other factors would explain it. Thank you.

[wildbill]

Don't you wish there was some way you could pay mags like NG or whatever BY THE STORY to read on line?

Looks like they'd make a ton of money from folks who don't want to subscribe or run down to the nearest Barnes & NOble to buy a copy.