At Moeraki, 40 kilometres south of Oamaru, huge spherical boulders are scattered along the beach. Others can be seen emerging from the sandstone cliffs. Each boulder weighs several tonnes and is up to two metres high.
According to Maori legend, the boulders are gourds washed ashore from the great voyaging canoe Araiteuru when it was wrecked upon landfall in New Zealand hundreds of years ago.
Scientists explain the boulders as calcite concretions formed about 65 million years ago. Crystallization of calcium and carbonates around charged particles gradually formed the boulders in a pearl-like process that took as long as four million years. The soft mudstone containing the boulders was raised from the seabed around 15 million years ago; waves, wind and rain are excavating them one by one.
The viewing platform, just a few minutes walk through regenerating native forest, offers an excellent view of the boulders. If you're lucky, you might also see Hector's dolphins playing in the waves.