What kinds of rock are they found in???
These old imprints are most commonly found in sedimentary rocks, which are made from layers of compacted rock. Over time, layers of sediments cover up the fossil. Sandstone, shale, and limestone are examples of rocks which hold fossils.
layers of rock with fossils (on the right)
How are fossils formed???
There are many ways which they can form, but there is one common process. When an animal dies in or near a wet enviorment, moist mud covers it up. Soon, it's body will be buried. Skin and tissues will decompose fast, leaving hard bones and imprints behind. More sediments build up over the fossil and turns it to rock.
The waters were calm and cool. A small fish swam through the sea, it's scales glistening gray with a tint of green. It's small beady eyes looked around for algae. But then, it sensed some movement in the water. Giving up the search for food, it tried to dart away. Where to hide?
Way, way down below there was a piece of coral. The fish tried to swim down there to hide. The thing behind him was getting closer and closer. It was relieved when the coral was just a tail-flick away. The fish desperately hurried over, only to see a wide open, toothy mouth. CHOMP! Then everything went black.
The dolphin had finally caught a meal. It was about to gobble up the dead fish when the dolphin spotted a huge great white shark who was also glad to find a decent snack. Startled, the dolphin dropped the fish. It sank, going deeper and deeper underwater. Disappointed but scared, the dolphin decided it was too late to go get it with a shark behind her. So it zipped away through the deep blue sea with the shark, leaving the body of the fish to settle down into the sand.
Some time passed. Sediments like sand and rock floated around and landed on the slowly decaying body of the fish. Years and years passed, and the soft skin and tissues in the fish's body decomposed leaving hard bones and imprints as the only remains of the fish. It was now covered with many layers of sediments. Soon the pressure of the water soon made those layers harden into rock.