The Moeraki Boulders are unusually large spherical boulders lying along a stretch of Koekohe Beach on the wave-cut Otago coast of New Zealand between Moeraki and Hampden. They occur scattered either as isolated or clusters of boulders within a stretch of beach where they have been protected in a scientific reserve. These boulders are grey-colored septarian concretions, which have been exhumed from the mudstone and bedrock enclosing them and concentrated on the beach by coastal erosion.
The most striking aspect of the boulders is their unusually large size and spherical shape, with a distinct bimodal size distribution. Approximately one-third of the boulders range in size from about 0.5 to 1.0 meter in diameter, the other two-thirds from 1.5 to 2.2 meters. Most are spherical or almost spherical, but a small proportion are slightly elongated parallel to the bedding plane of the mudstone that once enclosed them.
The Moeraki Boulders are concretions created by the cementation of the Paleocene mudstone of the Moeraki Formation, from which they have been exhumed by coastal erosion. The main body of the boulders started forming in what was then marine mud, near the surface of the Paleocene Sea floor. This is demonstrated by studies of their composition; specifically, the magnesium and iron content, and stable isotopes of oxygen and carbon. Their spherical shape indicates that the source of calcium was mass diffusion, as opposed to fluid flow.
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.This legend tells of the rocky shoals that extend seaward from Shag Point as being the petrified hull of this wreck and a nearby rocky promontory as being the body of the canoe’s captain. Their reticulated patterning on the boulders, according to this legend, are the remains of the canoe’s fishing nets.
Early morning and late afternoon are the prime times for photography, when brilliant soft sunlight is cast across the rocks; making for spectacular photographic opportunities. Other times, such as when storms are rolling in, provide an atmosphere and scene that can’t be matched anywhere else in New Zealand, or the world!
According to Wikipedia