Geschichte: A forest is a typical place where wood can be expected- unless it's up to 16 million years old. When I was walking home from Winterthur, I took a shortcut. Along a brook some rock material was exposed to the surface. I saw that one stone looked like there were carved rings on it, to me it looked like growth rings of a tree. This could be confirmed by grinding a smooth surface.
Geologie: This is a sample of petrified wood. It can be formed for example when a flood packs the piece of wood into an airtight layer of mud. If there are no living organisms left, it cannot get decomposed and therefore petrifies. This piece was found in the upper freshwater molasse which is an evidence that there must have been a forest in this region more than 5 million years ago.