Igneous and metamorphic rock types are found in gravels at the base of each of four distinct series of fluviatile deposits making up the four Pleistocene depositional terraces of Louisiana. Their rarity in exposures is accounted for by intense surface weathering. The igneous and metamorphic rock types appear to have been transported from the Lake Superior Upland and igneous areas of the Central Interior region. Their presence far south of their source and their peculiarities of size and roundness are attributed to the specialized and fluctuating conditions of Pleistocene time.

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