beds of past ages follow upon each other. In making these statements, I do not forget the immense length of the geological periods; on the contrary, I fully accede to it, and believe that it is more likely to have been underrated than overstated. But let it be increased a thousand-fold, the fact remains, that these new types occur commonly at the dividing line where one period joins the next, just on the margin of both. For years I have collected daily among some of these deposits, and I know the Sea-Urchins, Corals, Fishes, Crustacea, and Shells of those old shores as well as I know those of Nahant Beach, and there is nothing more striking to a naturalist than the sudden, abrupt changes of species in passing from one to another. In the second set of Cretaceous beds, the Neocomian, there is found a little Terebratula (a small Bivalve Shell) in immense quantities: they may actually be collected by the bushel. Pass to the Urgonian beds, resting directly upon the Neocomian, and there is not one to be found, and an entirely new species comes in. There is a peculiar Spatangus (Sea-Urchin) found throughout the whole series of beds in which this Terebratula occurs. At the same moment that you miss the Shell, the Sea-Urchin disappears also, and another takes its place. Now, admitting for a moment that the later can have grown out of the earlier forms, I maintain, that, if this be so, the change is immediate, sudden, without any gradual transitions, and is, therefore, wholly inconsistent with all our known physiological laws, as well as with the transmutation-theory.