Contending that Barth's 1931 article on "Proposed change in calculation of norms of rocks" is no more than a change in the manner of stating the norm, Chayes presents (and suggests that Barth has implied) two alternative methods of calculating wo, en, fs, fo, and fa that differ from the CIPW rules in that CaO, MgO, and FeO are not allocated to di, hy, and ol before allocation of SiO 2 . It is concluded that the CIPW method gives results closer in agreement to the mode. Barth points out, in reply, that his paper implied no changes in the principles of the CIPW rules of calculation, that the changes suggested for the presentation of the norm were accepted by H. S. Washington, who founded it, and gives excerpts from his paper in substantiation.

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