Petrographic examination of a body of intrusive igneous rocks in the White Mountain, or northern Inyo, Range of California and Nevada shows that certain facies have undergone extensive changes in composition and texture since their primary crystallization. These alterations include the albitization of the potash feldspars, the partial sericitization and epidotization of the plagioclase feldspars, and the formation of biotite, chlorite, magnetite, and other secondary minerals, with accompanying textural changes. To describe these modifications and to attempt to account for their origin is the purpose of this paper.

The peculiarities exhibited by these rocks attracted the attention of the writer while he was making a study of the general geology of the northern half of the White Mountain quadrangle. It soon became evident that changes in mineralogical and chemical composition were of such fundamental importance that they merited further study. Accordingly, portions of two summer field seasons and an . . .

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