About 16 000 years ago, climate warmed and glaciers began to retreat. As the glaciers melted, the sea covered low-lying areas pushed down by the weight of the ice. Clam shells in ancient seafloor clay layers found far above present sea level prove that much of Nanaimo was covered by the ocean 15 000 years ago. Shortly thereafter, the land, relieved of its ice load, rebounded and carried these marine deposits up above sea level.