These rocks appear to have markings on them. If this were a sentence, what would it say?
Precambrian stromatolites are fossils of ancient colonies of algae, which grew in layers, forming the beautiful striations seen here.
What ancient tree was this, before it was replaced with minerals and became petrified wood?
Detail showing crystals in the center.
Fossilized redwood at Yellowstone.
A geode full of amethyst crystals.
Shale formation, Lewis County, Kentucky.
And speaking of rocks...
Glacier National Park