Moeraki Boulders Otago NZ
The Moeraki Boulders are situated on Koekohe Beach at a place named Kumara, midway between Hampden and Moeraki townships in North Otago. Access to them is gained by a small one-way side road, 1 mile north along the main road from Hillgrove railway station. The boulders are grey-coloured septarian concretions, which have been eroded out by wave action from the cliffs of soft, black mudstone that back the beach. In places, partially exposed concretions can be seen in the cliffs. They originally formed on the sea floor when the mudstone was accumulating during the early Tertiary period some 60 million years ago. The largest concretions are traversed by cracks, filled by yellow calcite. In some the upper part is worn away; only a shell remains, looking like discarded segments of orange peel. The concretions weigh several tons and are up to 12 ft in circumference. Similar concretions are known on the north-facing foreshore of Shag Point, some 12 miles further south, but these are derived from older (upper Cretaceous) mudstone.