The `` Purbeck Marble '' of the Jurassic period and the `` Sussex Marble '' of the early Cretaceous period , which both occur in southern England , are limestones containing the tightly packed remains of the pond snail `` Viviparus '' .
The Purbeck Marble of the Jurassic period and the Sussex Marble of the early Cretaceous , which both occur in southern England , are limestones containing the tightly packed remains of the pond snail `` Viviparus '' .