The determination of the stability conditions of chlorite, especially the stability temperature between 500 degrees and 700 degrees C. by B. W. Nelson, D. M. Roy, R. Roy, and H. S. Yoder complements the conclusions arrived at from the microscopical study of the interstitial chlorite in the diabase-minverite series of south-west England. These disprove the assumption that the chlorite generally originates from metasomatic reaction or devitrification of a glassy residue. Considering the formation of chlorite at a late stage of solidification, an explanation of its genesis is attempted on that basis. Possible effects on the petrologic evolution are discussed. The chlorite taking part in the filling of amygdales and pseudo-amygdales has formed preferentially by replacement of carbonates. Variation in form, degree, and associated products is exemplified. The appearance of a liquid carbonate phase, ascertained by P. J. Wyllie, O. F. Tuttle, and R. I. Harker in the system calcite-wollastonite-water at temperatures between 640 degrees and 680 degrees C. seems to be realized likewise under natural conditions, and to provide a basis for the understanding of certain phenomena, especially in reaction zones.

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