Wells, borings, and excavations have shown that a thick zone of decayed rock or saprolite occurs on the buried surface of the gneiss and schist bedrock at many places throughout Long Island, New York. A concretionary rock at the top of the decayed zone was found during the period 1927 through 1929 in borings and in a shaft for a water supply tunnel in Brooklyn, but its significance was not at first realized. This rock is an ancient laterite or ferricrete, and its presence strongly reinforces the evidence furnished by the saprolite for the existence of a humid tropical climate for a long time preceding the deposition of the unconsolidated Cretaceous and younger sediments that make up the bulk of Long Island.

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