This paper summarizes first the results of a former study in which it was pointed out that a statistical relation existed, during the differentiation and solidification of the magma, between the three oxides TiO 2 , Fe 2 O 3 and FeO, contained in rocks and in titaniferous ores from the Adirondack Mountains. In the above magmas, the oxidation in the different rocks decreases as the differentiation proceeds and is at a minimum for the gabbroic rocks associated with the titaniferous ores. On the contrary, the ores seem to have a high oxidation index. This fact is in agreement with the evolution of residual solutions with which ores are in direct connection. The relations between gabbroic rocks and ores are discussed in detail. It is concluded that the TiO 2 concentration of ores is limited to about 30 percent (molecular percentage) relative to the total TiO 2 + Fe 2 O 3 + FeO mols (computed to 100 percent).The probability of a eutectic is discussed and its composition quantitatively fixed. This fact is checked and emphasized by the comparison of analyses of rocks and ores from the Adirondacks with many analyses of ores from other regions.

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