If I stumbled across the Moerki boulders without reading about them, I would think they were some sort of fossilized alien eggs. They totally look extraterrestrial and so are very interesting. Located near Oamaru, they are worth seeing.
How were they formed? Well, like almost everything else in New Zealand, there are two stories, one told by Maoris and the other told by scientists or geologists in this case, well, here are the two versions:
Maori Version : They are food baskets that were thrown ashore a very long time ago and therefore turned to stone.
Geological Version: The deposit of chemical concretions around hard cores millions of years ago under the sea formed these spherical boulders in softer rocks. When the sea was moved upward, they were pushed out of the softer rocks by the waves.