Plesiosaurus.
Along with this monster, another and still more singular deformity makes its appearance, the Plesiosaurus, in which the fabulous chimæras and hydras of antiquity seem to start into existence. Fancy a crocodile twenty-seven feet long, with the fins of a whale, the long and flexible neck of a swan, and a comparatively small head. With the appearance of this new tyrant, the last hope of escape is taken from the trembling fishes; for into the shallow waters, inaccessible to the more bulky Ichthyosaurus, the slender Plesiosaurus penetrates with ease.
A race of such colossal powers seemed destined for an immortal reign, for where was the visible enemy that could put an end to its tyranny? But even the giant strength of the saurians was obliged to succumb to the still more formidable power of all-changing time, which slowly but surely modified the circumstances under which they were called into being, and gave birth to higher and more beautiful forms.
In the tertiary period, the dreadful reptiles of the mesozoic seas have long since vanished from the bosom of the ocean, and cetaceans, walruses, and seals, unknown in the primitive deep, now wander through the waters or bask on the sunny cliffs. With them begins a new era in the life of the sea. Hitherto it has only brought forth creatures of base or brutal instinct, but now the Divine spark of parental affection begins to ennoble its more perfect inhabitants, and to point out the dim outlines of the spiritual world.
During all these successive changes the surface of the earth has gradually cooled to its present temperature, and many plants and animals that formerly enjoyed the widest range must now rest satisfied with narrower limits. The sea-animals of the north find themselves for ever severed from their brethren of the south, by the impassable zone of the tropical ocean; and all the fishes, molluscs, and zoophytes, whose organisation requires a greater warmth, confine themselves to the equatorial regions.
As the tertiary period advances towards the present epoch, the species which flourished in its prime become extinct, like the numberless races which preceded them; new modifications of life, more and more similar to those of the present day, start into existence; and, finally, creation appears with increasing beauty in her present rich attire.
Thus old Ocean, after having devoured so many of his children, has transformed himself at last into our contemporaneous seas, with their currents and floods, and the various animals and plants growing and thriving in their bosom.
Who can tell when the last great revolutions of the earth-rind took place, which, by the upheaving of mighty mountains or the disruption of isthmuses, drew the present boundaries of land and sea? or who can pierce the deep mystery which veils the future duration of the existing phase of planetary life?
So much is certain, that the ocean of the present day will be transformed as the seas of the past have been, and that "all that it inhabit" are doomed to perish like the long line of animal and vegetable forms which preceded them.
We know by too many signs that our earth is slowly but unceasingly working out changes in her external form. Here lands are rising, while other areas are gradually sinking; here the breakers perpetually gnaw the cliffs, and hollow out their sides, while in other places alluvial deposits encroach upon the sea's domain.