There is history in limestone

Limestone is a sedimentary rock, and along with shale, is one of the best preservers of fossils. Over time, sedimentary rock presses down around what were once living things to preserve the basic outline of their appearance and physical characteristics. Crack open a large piece of limestone or walk a beach covered with limestone rocks and you are almost guaranteed to find a fossil. If you don't find one, rest assured that they are there, lending the calcium carbonate from bones, exoskeletons and shells to the limestone itself.

Limestone forms when calcite from the water crystallizes or when fragments from coral and shells cement together. Limestone is a type of sedimentary rock that contains fossils in the form of sea creatures. Entire reef formations and communities of organisms are found preserved in limestone. The types of fossils found in limestone include coral, algae (see images), clams, brachiopods, bryozoa and crinoids. Most limestone forms in shallow tropical or subtropical seas. In some cases, fossils make up the entire structure of limestone.

Source: eHow