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Explanation of the Table on p. 149.
Column I. contains the names of the successive sedimentary strata.
Column„ II. contains the percentage of the duration of the various epochs, according to Williams, the time from the Cambrian until recent times being taken as 100.
Column„ III. gives the estimated duration in years of the Palæozoic, Mesozoic, and Cænozoic periods, according to Walcott.
Column„ IV. gives in years the duration of the various smaller epochs, as computed from Walcott and Williams' statements.
Column„ V. Representatives of stages of the ancestral line of man. The names stand in the level of the stratum in which they have made their first appearance.
Column„ VI. contains the number of years which, in the present calculation, have been assumed necessary for the animal to reach puberty.
Column„ VII. contains the number of generations which can have elapsed from stage to stage. For example, 60,000 generations separate the earliest known anthropoid apes from Pithecanthropus.
Let us follow the descent of man further back. The next stage, reckoning backwards, is that from Pithecanthropus to bonâ-fide anthropoid apes. They are represented in the Miocene by various genera—e.g., Pliopithecus and Dryopithecus. According to Croll and Wallace, 850,000 years ago carry us
