Chapter 6

_SPECIES AND TIME._

Two relations of species to time.--No evidence of past existence of minutely intermediate forms when such might be expected _a priori_.--Bats, Pterodactyles, Dinosauria, and Birds.--Ichthyosauria, Chelonia, and Anoura.--Horse ancestry.--Labyrinthodonts and Trilobites.--Two subdivisions of the second relation of species to time.--Sir William Thomson's views.--Probable period required for ultimate specific evolution from primitive ancestral forms.---Geometrical increase of time required for rapidly multiplying increase of structural differences.--Proboscis monkey.--Time required for deposition of strata necessary for Darwinian evolution.--High organization of Silurian forms of life.--Absence of fossils in oldest rocks.--Summary and conclusion ... _Page_ 128