Doubtfully realized at first, it has been slowly established through the heaping up of successive proofs, that in the waning years of that geological section of time called the Ice Age, man had begun this slow conquest of the earth.
All geological periods are text book accidents, or professional conveniences. The diorama of geological change was a continuous evolution of physics and topography, the rolling ages did not halt at sectional points, the mechanism of Creation did not stop at intervals to permit the introduction of a new set of designs and preparations, a new web of structural fancies and ideas, a new _modus operandi_ and a new _modus vivendi_.
Neither can we contend for moments of catastrophic intervention and the sudden release of Omnipotent mandates, sweeping away what had previously lived, and inundating the regions of life with irruptions of new forms.
The movement of life beginning within the recesses of Archæan time went on in its progress from a few centres of creation, until as age succeeded age, and the first utterances of life began to fill the voids of ocean and land, the kingdoms of animal being slowly possessed the earth.
And yet it is also true that the course of organic evolution in the records of palæontology expresses an Intention accomplishing its purpose under resistance. It conforms in the phenomena it presents to the conception of a Mind pursuing a purpose with an accelerated motion as that purpose was approached. For what is that record of extinct life?
From the first scintillations of life in the Cambrian era to the last contributions of Zoic energy in the Tertiaries, we see a succession of ascending stages of life, a series of zoological platforms which are linked together by a stairway of organisms passing from one to the next, and separated by a disappearance of forms which never reappear. Resistance is periodically overcome, but by it the intention of a Supreme Mind to produce the highest and widest and deepest life is forced into a display of creative energy.
In the earlier ages--the Palæozoic--the invertebrates appear in greater numbers, and the lower orders of plants, and only the preparatory groups of the vertebrates force their prophetic outlines in view, the invertebrates and plants begin in more generalized forms, and advance to the more specialized, which are the higher.