When we first moved here, we noticed lots of round-ish rocks, which we later found out were "geodes." They are generally hollow inside, and contain crystals of calcite, amethyst, or other minerals. In fact, there's a house not far from here where the entire central chimney and front porch structure are made from geodes. We're using them for landscaping all around the house.
Well, one of these has been on the back deck since we moved in. Just the other day, I noticed (and Barry photographed) something unusual on the surface of the geode.
A bit of research (isn't Wikipedia wonderful?) shows that it's a fossil trilobite, a little marine creature much like a modern horseshoe crab. There are over 20,000 species of trilobites and they range in age from 250 to 500 million years old.
A bit more research and I sort of figured that our little trilobite died and was laid down in the sediment at the bottom of the Ordovician ocean about 450 million years ago. At that time, most of the US and Canada were submerged under a shallow, warm ocean somewhere near where the equator was then.
You never know what's out there until you open your eyes, I guess.