What rock is it

The remains of the dead sea animal settle to the bottom of the sea

limestone

The rock you are referring to is limestone. Limestone is a sedimentary rock that forms from the accumulation of the remains of dead sea animals, such as shells and coral, at the bottom of the sea. Over time, the layers of these organic remains undergo compaction and cementation, resulting in the formation of limestone. To identify this rock, you can look for fossilized remains of sea creatures embedded within it.