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Evidence is presented to show that modern mollusk shells from rivers can have anomalous radiocarbon ages, owing mainly to incorporation of inactive (carbon-14-deficient) carbon from humus, probably through the food web, as well as by the pathway of carbon dioxide from humus decay. The resultant effect, in addition to the variable contributions of atmospheric carbon dioxide, fermentative carbon dioxide from bottom muds, and, locally, of carbonate carbon from dissolving limestones, makes the initial carbon-14-activity of ancient fresh-water shell indeterminate, but within limits. Consequent errors of shell radiocarbon dates may be as large as several thousand years for river shells.

Studies of phase equilibria by the method of quenching show that there are no ternary compounds at liquidus temperatures in the system Mg0-Crz03-Si02. There is an extensive twoliquid region, and the stability fields of periclase, picrochromite, and chromic oxide extend across most of the diagram. Temperatures of liquid formation are sufficiently high that a number of different compositions can be suggested for refractory purposes. Fundamental explanations are brought out for the improvement of chromite and chromite-forsterite refractories by the addition of MgO and for the improvement of chromite-silica refractories by the addition of chromic oxide or some other high-chromium compound.

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