And not only so, but, while this unity of creation prevails throughout the entire epoch as a whole, there is the same variety of geographical distribution, the same circumscription of faunae within distinct zooelogical provinces, as at the present time.  The Fishes of Massachusetts Bay are not the same as those of Chesapeake Bay, nor those of Chesapeake Bay the same as those of Pamlico Sound, nor those of Pamlico Sound the same as those of the Florida coast.  This division of the surface of the earth into given areas within which certain combinations of animals and plants are confined is not peculiar to the present creation, but has prevailed in all times, though with ever-increasing diversity, as the surface of the earth itself assumed a greater variety of climatic conditions.  D’Orbigny and others were mistaken in assuming that faunal differences have been introduced only in the last geological epochs.  Besides these adjoining zooelogical faunae, each epoch is divided, as we have seen, into a number of periods, occupying successive levels one above another, and differing specifically from each other in time as zooelogical provinces differ from each other in space.  In short, every epoch is to be looked upon from two points of view:  as a unit, complete in itself, having one character throughout, and as a stage in the progressive history of the world, forming part of an organic whole.

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As the Jurassic epoch was ushered in by the upheaval of the Jura, so its close was marked by the upheaval of that system of mountains called the Cote d’Or.  With this latter upheaval began the Cretaceous epoch, which we will examine with special reference to its subdivision into periods, since the periods in this epoch have been clearly distinguished, and investigated with especial care.  I have alluded in the preceding article to the immediate contact of the Jurassic and Cretaceous epochs in Switzerland, affording peculiar facilities for the direct comparison of their organic remains.  But the Cretaceous deposits are well known, not only in this inland sea of ancient Switzerland, but in a number of European basins, in France, in the Pyrenees, on the Mediterranean shores, and also in Syria, Egypt, India, and Southern Africa, as well as on our own continent.  In all these localities, the Cretaceous remains, like those of the Jurassic epoch, have one organic character, distinct and unique.  This fact is especially significant, because the contact of their respective deposits is in many localities so immediate and continuous that it affords an admirable test for the development-theory.  If this is the true mode of origin of animals, those of the later Jurassic beds must be the progenitors of those of the earlier Cretaceous deposits.  Let us see now how far this agrees with our knowledge of the physiological laws of development.