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In 1922, N. L. Bowen presented his carefully considered opinions and supporting data on the behavior of inclusions in magmas. That paper was one of the finest contributions of this able and versatile petrologist. Its ideas have been widely accepted, considerably discussed, and only slightly, if at all, modified. Nevertheless, field geologists who find inclusions in magmatic rocks do not always find convincing evidence as to origins, and even those who accept Bowen’s ideas may, with lack of data in a specific instance, ignore those ideas or assume that the evidence favors one or another origin. The evidences used need critical discussion. This study offers a summary of criteria and gives some new data for several districts. Emphasis is given to criteria used since Bowen’s paper was issued. Most of the problems lie in the dark spots, “black knots,” of granitic or dioritic rocks, but some attention is . . .

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