Limestone is called limestone because it has lime in it from the sea water it if formed in.
The hard shells of living things produce some kinds of limestone. How dopes limestone form? Limestone forms in the ocean, many living things, including coral, clams, oysters, and snails, have shells...
Limestone Caves e.g The Marble Arch Caves in Northern Ireland(Fermanagh)
This depends on the size of the limestone deposit, the rate of extraction and the economic viability of the deposit.
Stone and the burren