Note 2 — Chapter I · ON THE DIFFERENTIATION OF MAN FROM THE ANTHROPOIDS
Reading edition
Estimated duration of the Cainozoic Period, assuming that the thickness of the deposits is about 63,000 feet, and that deposits accumulate at the rate of 1 foot in 100 years. Drawn to the scale of 1 mm. to 100,000 years. The estimate is given and explained by Prof. Sollas in the Quarterly Journal of the Geological Society, LXV. (1909). The “tree” is based on that given by Dr. A. Keith in The Antiquity of Man, p. 509.
If we suppose the differentiation of the Hominidæ to have begun before the close of the Oligocene, about (say) 3,500,000 years are allowed for the evolution of the existing species of Man. All these reckonings are provisional.