In 1881 I presented before the American Association for the Advancement of Science the first definite announcement of the hypothesis of recurrent faunas, applying it to the fauna of the Marcellus, Genesee, and Ithaca black shales of new York, which I then conceived to be represented by the continuous fauna of the black shales of Ohio, Indiana, Kentucky, and Tennessee; and also, in the same paper, the hypothesis of shifting of faunas was applied to the Hamilton and Chemung faunas of central New York.2 Since that time a large amount of evidence has been accumulated confirming these hypotheses. These hypotheses are intimately correlated. Eecurrence or the departure of a fauna, its replacement by another, and its final reappearance in the same section at a higher level become the facts on which the hypothesis of shifting of the faunas is based; and the . . .