As the intention is to embrace higher zoological and structural ideas, this again awakens resistance, and we see its gradual repulse. These periodic floodings or gushes of forms of life, as the brachiopods in the Silurian, the trilobites in the upper Potsdam, and crustacea in modern seas, the bivalves in the Devonian, the crinoids in the Lower Carboniferous, the echinoids in the Cretaceous, the cephalopods and reptiles in the Jurassic, the gastropods and mammals in the Tertiaries, are the wide escape of a propulsive intention as it overcomes resistance, which it has undermined or repelled by processes of development, slowly and unintermittently inaugurated long before.
Premonitions of these outbursts are found before they come, in the genera and orders of the preceding era. So striking is this that it has led M. Naudin, a French naturalist, with no theological hobbies or convictions, to propound, on the evidence, the analogous idea, that a force of variation or origination of forms has acted rhythmically or unintermittently, because each movement was the result of the rupture of an equilibrium, the liberation of a force which till then was retained in a potential state, by some opposing force or obstacle, overcoming which, it passes to a new equilibrium, and so on.
Hence stages of dynamic activity and static repose, of origination of species and types, alternated with periods of stability or fixity. The time-piece does not run down regularly, but “la force procede par saccades; et par pulsation d’autant plus energiques que la nature etait plus près de son commencement.”
Now, it is a remarkable circumstance, strengthening the Doctrine of Intention, that the vast length of time involved in the progress of the Palæozoic Ages was employed in establishing the kingdoms of invertebrate life, and that as at its close, the vertebrate type was reached (in which resided the potential power of the highest development) the Supreme Will rose swiftly to its object--Man, his powers and destiny!
Resistance accumulated against the flow of that intention, and by obstruction attempted to close its exit into the pregnant channel of vertebrate forms. This resistance was slowly dissipated through the prolific avenues of invertebrate life. And the Intending Mind, having ushered in the vertebrates, thence proceeds with rapidity through its evolving phases to complete its organic purpose, creating Man, and pushing in upon the world’s stage the vast psychic consequences of this supreme result.