These are tumble polished agates from the beach at Birdlings Flat, on Banks Peninsula, just before the township of Little River. A wide variety of different coloured stones can be found here, including petrified wood, and the occasional piece of rhodonite. The stones have all drifted north on ocean currents from rivers such as the Rangitata, Ashburton Hinds, and other rivers further to the south. The ocean current sweeping from the south encounters Banks Peninsula, and the less dense salt water there, thus depositing the stones.
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