Approximately 1,000 shale samples were analyzed by X-ray-fluorescence spectrography for the elements Na, Mg, Al, Si, K, Ca, Fe, Rb, and Sr. Three quarters of the samples came from two completely cored sections of mainly Upper Cretaceous shale in eastern and central Saskatchewan; most of the remainder came from cored Jurassic and Triassic sections in western Queensland, Australia. Preliminary results indicate that diadochic substitution of minor elements in the clay minerals is controlled by the chemistry of the waters in which the clays were deposited. The Rb/K ratio in particular appears to be significantly higher for marine shale than for continental shale.

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