SOCIAL DIFFERENTIATION AND INTEGRATION 737
years more, rolled away before the faintest traces of mammalian life presented themselves well up in the New Red Sandstone or Triassic period, and during that and the next or Jurassic period, each of which lasted at least 3,000,000 years, the world was given over to amphibian and reptilian forms and to a cryptogamic and gymnospermous vegetation. It is only in the Cretaceous period succeeding the Jurassic, and occupying another 3,000,000 years, that anything like the now dominant forms of either plants or animals became common. At the close of the Cretaceous all but one twenty-fourth part of the earth's life-history had passed, and as yet there were no four-footed beasts such as make up the chief part of the present fauna of the globe. The Ter- tiary period was ushered in, estimated likewise at nearly 3,000,- 000 years, and it was during this comparatively brief space of time that all the great products of nature were evolved. Before it closed all the great families of animals, including the apes, were in existence. Whether man can be numbered among the products of late Tertiary (Pliocene) time is a question now under discussion, but the bulk of the evidence is in the negative. That is to say, it is generally conceded that the creature resembling man that has left relics of either his skeleton or his handiwork in the late Tertiary strata, was not really man, but the ancestor of man Pithecanthropus, Homosimius, or whatever name may be given to it.
Man properly so called was of later or Quaternary origin. He came into existence somewhere below the terminal moraine, while the several glacial periods were successively chasing the arctic plants and animals from their north temperate homes and stranding them on the mountain tops of Europe. The duration of this period is variously estimated by geologists. Few place it higher than 500,000 years, and the consensus of opinion seems to vary from 200,000 to 300,000 years. It is therefore tolerably safe to say that the entire human period cannot exceed 300,000 years. But during at least seven-eighths of this period man was scarcely more than an animal. This was the period of social differentiation described at the beginning of this article. In it man overspread the globe, and he divided up into a multitude of
