Geology
Herald Island is composed of sedimentary, metamorphic, and igneous rocks. The northeastern tip of this island consists of a 600 m (1,969 ft)-thick sequence of sandstone, phyllite, quartzose sandstone, quartz-chlorite-sericite schist mylonite, and cataclastic quartz syenite. These rocks are of either Proterozoic or Late Paleozoic age. The bulk of this island consists of a Jurassic granite pluton.
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