Some deposits of brucitic limestone with a ratio of MgO: CaO higher than that of dolomite are described. Evidence is given to show that the excess magnesia derived from dissociation of dolomite by the heat of the adjacent granite. Selective transfer of the products of dissociation into the carbonate rocks is attributed to igneous emanations. The bulk of the brucite is believed to have been deposited by direct replacement of carbonates, rather than by hydration of previously formed periclase, as has been suggested for similar occurrences elsewhere.

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