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.

There is a very singular group of Ammonites in the Cretaceous epoch,
which, were it not for the suddenness of its appearance, might seem
rather to favor the development-theory, from its great variety of
closely allied forms. We have traced the Chambered Shells from the
straight, simple ones of the earliest epochs up to the intricate and
closely coiled forms of the Jurassic epoch. In the so-called Portland
stone, belonging to the upper set of Jurassic beds, there is only one
type of Ammonite; but in the Cretaceous beds, immediately above it,
there set in a number of different genera and distinct species,
including the most fantastic and seemingly abnormal forms. It is as if
the close coil by which these shells had been characterized during the
Middle Age had been suddenly broken up and decomposed into an endless
variety of outlines. Some of these new types still retain the coil, but
the whorls are much less compact than before, as in the Crioceras; in
others, the direction of the coil is so changed as to make a spiral, as
in the Turrilites; or the shell starts with a coil, then proceeds in a
straight line, and changes to a curve again at the other extremity, as
in the Ancyloceras, or in the Scaphites, in which the first coil is
somewhat closer than in the Ancyloceras; or the tendency to a coil is
reduced to a single curve, so as to give the s