Unless we are prepared to ignore all these considerations and deny that Croll's theory, as amended by Sir R. Ball, has had any appreciable effect on the conditions of the glacial period, it follows with mathematical certainty, that this period, taking it from the commencement of the great refrigeration in the Pliocene to its final disappearance in the Recent, must have lasted for about 200,000 years. And as man clearly existed in the pre-glacial period, and was already widely spread and in considerable numbers in the early glacial, 250,000 years may be taken as an approximation to the _minimum_ duration of the existence of the human race on the earth. To this must be added an indefinitely long period beyond, unless we are prepared to disprove the apparently excessively strong evidence for its existence in the Pliocene and even in the Miocene periods; evidence which has been rapidly accumulating of late years; and to which, as far as I know, there has been no serious and unbiassed attempt at scientific refutation; and to which confirmation is given by the undoubted fact that the Dryopithecus, the Hylobates, and other quadrumana, closely resembling man in physical structure, already existed in the Miocene, and, if Professor Ameghino's discoveries referred to at p. 264 are confirmed, in the vastly more remote period of the early Eocene. CHAPTER X. QUATERNARY MAN. No longer doubted--Men not only existed, but in numbers and widely spread--Palæolithic Implements of similar Type found everywhere--Progress shown--Tests of Antiquity--Position of Strata--Fauna--Oldest Types--Mixed Northern and Southern Species--Reindeer Period--Correspondence of Human Remains with these Three Periods--Advance of Civilization--Clothing and Barbed Arrows--Drawing and Sculpture--Passage into Neolithic and Recent Periods--Corresponding Progress of Physical Man--Distinct Races--How tested--Tests applied to Historical, Neolithic, and Palæolithic Man--Long Heads and Broad Heads--Aryan Controversy--Primitive European Types--Canon Taylor--Huxley--Preservation of Human Remains depends mainly on Burials--About forty Skulls and Skeletons known from Quaternary Times--Summary of Results--Quatrefages and Hamy--Races of Canstadt--Cro-Magnon--Furfooz--Truchere--Skeletons of Neanderthal and Spy--Canstadt Type oldest--Cro-Magnon Type next--Skeleton of Cro-Magnon--Broad-headed and Short Race resembling Lapps--American Type--No Evidence from Asia, Africa, India, Polynesia, and Australia--Negroes, Negrillos, and Negritos--Summary of Results.