Plots of the principal elements Si, Al, Fe for normal clastic sediments reveal a very definite geochemical trend for these elements. Al/Fe ratios lie between 1.5 and 2.5 while Si is continuously variable but has clearly distinguishable ranges for each of the currently used sediment types when plotted on a Si-Al-Fe ternary diagram. Igneous rocks undergoing weathering tend to move in composition toward the Si, Al, Fe "main sequence" and later separate by hydraulic sorting toward either the coarser quartzose sandstone or finer shale ends of this sequence. The results indicate the possibility of clarification of existing classifications and of determining the parent-rock types of certain metasediments.

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