LAW OF PROGRESS AND APPEARANCE OF GROUPS 251 



of Primates in the so-called primitive fauna of 

 Cernay and of Puerco is particularly instructive, 

 and constitutes a highly valuable argument against 

 the theory of the continued progress of beings. 

 It is in vain that Dr. Lemoine, in his fine researches 

 on this lower Eocene fauna of the environs of 

 Rheims, has attempted to prove that it was im- 

 possible to include the Mammals of Cernay in 

 the orders of existing Placentals ; the differentiation 

 of the great groups, though less perfect than in 

 more recent faunas, is none the less obvious to a 

 palaeontologist, and forcibly leads us to the convic- 

 tion that these Placentals of the very lowest Eocene 

 possessed a long line of ancestors dating from 

 Secondary times. But here we ace verging upon the 

 unknown, and every possible hypothesis has been 

 proposed for finding a centre of dispersion for the 

 Placentals, sometimes in the Arctic Continent, and 

 sometimes in some Pacific Continent supposed to 

 have disappeared by subsidence. If the recent 

 data brought by F. Ameghino to the study of 

 the faunas of the Cretacean Mammals of Patagonia 

 are confirmed from a stratigraphic point of view, 

 it would perhaps be expedient to seek in the 

 Continent of South America for the real primitive 

 ancestors of our Tertiary Primates and Ungulates. 

 Even for the most specialized groups, such as 

 the Proboscidians, the recent discovery in the 

 Oligocene of the Libyan desert, of the Palceo- 

 mastodons, the ancestral forms of our Miocene and 

 Pliocene Mastodons show us at what remote period 

 in the geological past we shall one day discover 

 the points of differentiation of each branch. 



