Fossils refers to the preserved remains of ancient life, such as bones, teeth, wood, and shells.
Fossil brachiopods are examples of marine fossils. Fossils brachiopods in sedimentary rocks indicate ancient marine environments. Brachiopods was the most common shelled animal in the ancient seas.
Therefore; any rock with lots of shells; brachiopod, sponges, corals, or bryozoans was deposited in the oceans and indicates that the rock layes was once at the bottom of an ocean.
