But soon began to emerge from all these discoveries a fact of enormous importance. The skulls and bones found at Cro Magnon, Solutre, Furfooz, Grenelle, and elsewhere, were compared, and it was thus made certain that various races had already appeared and lived in various grades of civilization, even in those exceedingly remote epochs; that even then there were various strata of humanity ranging from races of a very low to those of a very high type; and that upon any theory--certainly upon the theory of the origin of mankind from a single pair--two things were evident: first, that long, slow processes during vast periods of time must have been required for the differentiation of these races, and for the evolution of man up to the point where the better specimens show him, certainly in the early Quaternary and perhaps in the Tertiary period; and, secondly, that there had been from the first appearance of man, of which we have any traces, an UPWARD tendency.(191) (191) For Wesley's statement of the amazing consequences of the entrance of death into the world by sin, see citations in his sermon on The Fall of Man in the chapter on Geology. For Boucher de Perthes, see his Life by Ledieu, especially chapters v and xix; also letters in the appendix; also Les Antiquities Celtiques et Antediluviennes, as cited in previous chapters of this work. For an account of the Neanderthal man and other remains mentioned, see Quatrefages, Human Species, chap. xxvi; also Mortillet, Le Prehistorique, Paris, 1885, pp. 232 et seq.; also other writers cited in this chapter. For the other discoveries mentioned, see the same sources. For an engraving of the skull and the restored human face of the Neanderthal man, see Reinach, Antiquities Nationales, etc., vol. i, p. 138. For the vast regions over which that early race spread, see Quatrefages as above, p. 307. See also the same author, Histoire Generale des Races Humaines, in the Bibliotheque Ethnologique, Paris, 1887, p. 4. In the vast mass of literature bearing on this subject, see Quatrefages, Dupont, Reinach, Joly, Mortillet, Tylor, and Lubbock, in works cited through these chapters.