316 PROCEEDINGS OF THE ACADEMY OF [1887. 



conditions of relationship or divergence obtain among the older Terti- 

 ary deposits. It is well known to geologists that in most regions where 

 Tertiary deposits are developed, the faunal relationship existing 

 between the Eocene and Miocene series is a very restricted one ; in- 

 deed, in some regions it would appear that there is scarcely a single 

 species of fossil held in common by the two classes of deposits. This 

 is very largely the case in France, and perhaps more particularly 

 in the Eastern United States, Avhere the respective faunas are 

 practically wholly distinct. It is true that, in some regions, a careful 

 analysis of the formations now frequently referred to the Olig- 

 oeene has shown a number of connecting forms, and has brought the 

 two formations in closer relationship with each other, but the uni- 

 ting bond, as compared with that which unites the Pliocene with 

 the Post-Pliocene, or the Tertiary with the post-Tertiary, is still very 

 weak. In the Oligocene (Vicksburg) deposits of the United States, 

 for example, it is doubtful if the number of transgressional forms 

 uniting with the Miocene numbers more than six, and possibh' not 

 that many, out of a total of some 150 species. 



These facts being admitted, it can scarcely be argued further that, 

 with our existing classification as a basis, there remains any valid 

 reason for separating, as a distinct system, the Post-Pliocene (post- 

 Tertiary) series from the Tertiary (Pliocene). It may, however, still 

 be contended that we allow too much latitude to the Pliocene, and 

 that with a proper restriction to boundaries in which the recent fau- 

 nal element does not exceed 70 or 75 per cent, instead of rising to 

 85 and 90, or more, room may be had for a major series with a 

 largely peculiarized fauna. But even with this limitation the fau- 

 nal break separating a post-Tertiary series from the upper member 

 of the Tertiary (Pliocene), would scarcely be as great, and in most 

 cases not nearly so great, as that separating the Pliocene from the 

 Miocene, or the Miocene (or Oligocene) from the Eocene. 



Apart from the matter of mere numbers as indicating a lack of 

 of peculiarity in the post- Tertiary fauna, it may be urged that 

 there are yet certain elements in it which serve broadly to distin- 

 guish it from the faunas immediately preceding, and which would 

 <intitle it to the claim of a true system-fauna. Thus, as has fre- 

 quently been claimed, we have here the first evidences of man, and, 

 therefore, the expression of a so-called "Psychozoic" era; the remains 

 of a remarkable series of large edentate animals Megathermm, Mylo- 

 don, Megalonyx, Gli/ptodon, etc. foreign to the earlier faunas, yet 



