618 



PSYCHOZOIC ERA— AGE OF MAN— RECENT EPOCH. 



Fig. 982. — Diagram illustrating the Appearance and Extinction 

 of Successive Mammalian Faunae. 



disappeared since the beginning of the Miocene. The Miocene mam- 

 malian fauna is totally different from the Eocene ; the Pliocene totally 

 different from the Miocene ; the Quaternary from the Pliocene ; and 

 the present from the Quaternary. This is graphically represented in 

 the diagram, Fig. 982, in which the alternate shaded and white spaces 



represent five con- 

 secutive mammalian 

 faunas (there are 

 really many more 

 than five) overlap- 

 ping each other, but 

 substantially distinct. 

 It seems in the high- 

 est degree improbable that man, a mammal, should survive the appear- 

 ance and disappearance of several mammalian faunas. 



Or, again, to put it still another way : We have seen (p. 537, Fig. 

 917) that, speaking generally, existing mammalian species commenced 

 to be introduced in the Quaternary ; existing genera in the Pliocene ; 

 and existing families in the Miocene. If, therefore, a tool-making 

 animal should be found in the Miocene, as some believe, it might be of 

 the family of Hominidai, but not the genus homo. If such should be 

 found in the Pliocene, it might be of the genus homo, but not the spe- 

 cies sapiens. Even the earliest Quaternary man — the so-called Nean- 

 derthal race — is supposed by Mortillet to have been a different species 

 from existing man. 



Time since Man appeared. — Geology reckons her time in periods, 

 epochs, etc. ; History hers in years. It is impossible to express the 

 one chronology in terms of the other except in a very rough approxi- 

 mative way, for want of a reliable common measure. If Mr. Croll's 

 theory of glacial cold should indeed prove true, then we might hope to 

 measure man's time on the earth with some degree of accuracy. But 

 in the absence of confidence in this theory, our only resource is to use 

 the measure which we have already used on several occasions, viz., the 

 effects of causes now in operation. This measure, however, can give 

 but very rough approximate results. 



There is no doubt that very great changes, both in physical geog- 

 raphy and in the mammalian fauna, have taken place since man ap- 

 peared. Judging by the rate of changes still in progress, we are natu- 

 rally led to a conviction of a lapse of time very great in comparison 

 with that recorded in history On the other hand, some attempts to 

 estimate more accurately by means of the growth of deltas in which 

 have been found implements of the Roman age, the Bronze age, and 

 the Stone age ; and by the progressive erosion of lake-shores and the 

 recession of waterfalls, which is supposed to have commenced after 



