Not a few discoveries have been made, apparently extending the existence of man to a much more remote antiquity, that of Miocene times. M. l'Abbé Bourgeois has collected, from undoubted Miocene strata at Thenay, supposed flint implements which he conceives to exhibit evidences of having been fashioned by man, as well as stones showing in some cases traces of the action of fire, and which he supposes to have been used as pot-boilers. M. Carlos Ribeiro has made similar discoveries of worked flints and quartzites in the Pliocene and Miocene of the Tagus; worked flint has been found in the Miocene of Aurillac (Auvergne) by M. Tardy, and a cut rib of _Halitherium fossile_, a Miocene species, by M. Delaunay at Pouancé. Very divided opinions are entertained as to the interpretation of the supposed implements discovered by M. l'Abbé Bourgeois. M. Quatrefages, after a period of doubt, has espoused the view of their being of human origin, and of Miocene age. "Since then," he says, "fresh specimens discovered have removed my last doubts. A small knife or scraper, among others, which shows a fine regular finish, can, in my opinion, only have been shaped by man. Nevertheless, I do not blame those of my colleagues who deny or still doubt. In such a matter there is no very great urgency, and, doubtless, the existence of Miocene man will be proved, as that of Glacial and Pliocene has been, by facts." Mr. Geikie, from whose work--_Prehistoric Europe_--I have summarized the above statements, says, in reference to this question: "There is unquestionably much force in what M. Quatrefages says; nevertheless, most geologists will agree with him that the question of man's Miocene age still remains to be demonstrated by unequivocal evidence. At present, all that we can safely say is, that man was probably living in Europe near the close of the Pliocene period, and that he was certainly an occupant of our continent during glacial and interglacial times." Professor Marsh considers that the evidence, as it stands to-day, although not conclusive, "seems to place the first appearance of man [in America] in the Pliocene, and that the best proofs of this are to be found on the Pacific coast." He adds: "During several visits to that region many facts were brought to my knowledge which render this more than probable. Man, at this time, was a savage, and was doubtless forced by the great volcanic outbreaks to continue his migration. This was at first to the south, since mountain chains were barriers on the east," and "he doubtless first came across Behring's Straits."