How strange and inexplicable is this perishing of types in the geological ages! Some we could well spare. We would not wish to have our coasts infested by terrible sea saurians, or our forests by carnivorous Dinosaurs. Yet why should these tyrants of creation so utterly disappear without waiting for us to make war on them? Other types we mourn. How glorious would the hundreds of species of Ammonites have shone in the cases of our museums, had they still lived! What images of beauty would they have afforded to the poets who have made so much of the comparatively humble Nautilus! How perfectly, too, were they furnished with all those mechanical appliances for their ocean life, which are bestowed only with a niggardly hand on their successors! Nature gives us no explanation of the mystery.
“From scarped cliff and quarried stone,
She cries—‘A thousand types are gone.’”
But why or how one was taken and another left she is silent, and I believe must continue to be so, because the causes, whether efficient or final, are beyond her sphere. If we wish for a full explanation, we must leave Nature, and ascend to the higher domain of the Spiritual.
THE NEOZOIC AGES.
Between the Mesozoic and the next succeeding time which may be known as the Neozoic or Tertiary,[AG] there is in the arrangements of most geologists a great break in the succession of life; and undoubtedly the widespread and deep subsidence of the Cretaceous, followed by the elevation of land on a great scale at the beginning of the next period, is a physical cause sufficient to account for vast life changes. Yet we must not forget to consider that even in the Cretaceous itself there were new features beginning to appear. Let us note in this way, in the first place, the introduction of the familiar generic forms of exogenous trees. Next we may mention the decided prevalence of the modern types of coral animals and of a great number of modern generic forms of mollusks. Then we have the establishment of the modern tribes of lobsters and crabs, and the appearance of nearly all the orders of insects. Among vertebrates, the ordinary fishes are now introduced. Modern orders of reptiles, as the crocodiles and chelonians, had already appeared, and the first mammals. Henceforth the progress of organic nature lies chiefly in the dropping of many Mesozoic forms and in the introduction of the higher tribes of mammals and of man.