Sediment samples collected from the bed of the Mississippi River show a considerable variation in grain size and degree of sorting. A study of pairs of samples, from adjacent points in the River, which differ in one or both of these features, indicates that these variations produce such differences in mineral composition that accurate mineralogical comparison of the samples is not possible on the basis of the usual methods of analysis and comparison. Various comparison methods were therefore tested. The most successful one, which eliminates most of these differences in mineral composition, is recommended for use in any study of sediments involving the detailed mineralogical comparison of a series of samples differing in average grain size or sorting.

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