The author has collected 168 chemical analyses from the literature. All analyses with less than 5 per cent Al2O3 (“quartzite” clan) were removed. The remaining analyses were divided on a tectonic basis into three clans; taphrogeosynclinal, eugeosynclinal, and others (mainly exogeosynclinal). Histograms for the seven major oxides and variation diagrams for K2O/Na2O and alkalies/Al2O3 indicate that the tectonic associations group together clans of chemical analyses which differ significantly from each other. The eugeosynclinal graywackes especially differ from other sandstones by their low K2O/Na2O ratio, which is correlated with the presence of basic volcanic detritus. Arithmetic and geometric means for the seven major oxides for the four clans are as follows (given to two significant figures):

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