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The paper presents a chemical composition diagram which permits easy comparisons of igneous rock compositions on the basis of aggregate cafemic oxides, FeO + Fe 2 O 3 , FeO, MgO, MgO + CaO, Na 2 O, K 2 O, Al 2 O 3 , and SiO 2 . The paper is illustrated by ten figures depicting chemical compositions of igneous rocks from British petrographic provinces and sub-provinces; also by two figures dealing with provinces of types which are poorly represented in Britain. These figures are supplemented by a proforma, drawn to the same scale, on which new analyses can be plotted.
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William Elrick Fraser (1962) studied this question.
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