The sea shell investigation You can put a collection of sea shells into a plastic container with a few small pebbles. If you shake the container hard for 15 seconds and pour out the results, they will look like the shells in figure 2.1. If the shells are broken, there must have been a similar shell-breaking process when they were deposited. Nature's version of the shaken container would be violent waves on a shelly beach or in a shallow sea. If the shells in the limestone are not broken, they must have been laid down in a quiet area.
Many limestones contain coral .
This tells us about the likely climate and depth of the sea when they were formed. Most corals today grow in shallow tropical seas, so we think that most coral-containing limestones formed in similar conditions. Most limestones are made mainly of fossil fragments. Therefore they must have been formed in an environment with lots of shelly life. Tropical shallow seas are like this today so this is where ancient limestones with fossils probably formed.