1887.] NATURAL SCIENCES OF PHILADELPHIA. 315 



ure has been only loosely, or not at all, adhered to. What, it might 

 be asked, are the claims of the Post-Pliocene and recent formations 

 to being considered a distinct system ? Viewed in its fannal as- 

 pects, the question may be very readily disposed of: the formations 

 in question have no claim to such recognition. If the formations 

 from the Eocene to the Pliocene inclusive are justly considered to 

 constitute, by virtue of their faunal unity, a distinct system, the 

 Tertiary, then manifestly the post-Tertiary (Post-Pliocene to recent) 

 must be a jiart of the same system, since its faunal ties unite it infin- 

 itely more closely with the more recent members of the Tertiary than 

 the individual members of the latter are united among themselves. 

 Thus the Eocene or Oligocene is further removed faunally from the 

 Miocene than the Pleistocene is from the Pliocene ; and the same rela- 

 tion holds with the Miocene and Pliocene. Lyell, himself the framer 

 of the now very generally accepted classification of the post-Cretaceous 

 deposits, admits that in the so-called Newer Pliocene deposits of 

 Sicily the percentage of recent molluscan forms rises as high as 90, 

 or even higher, consequently reducing the faunal peculiarity to less 

 than 10 per cent. In the Chillesford beds of Suffolk, England, the 

 faunal peculiarity is reduced to about 15 per cent, and in the Nor- 

 Avich or Fluvio-Marine Crag to 16 per cent. Again, the uppermost 

 of the Subapennine deposits of Northern Italy, forming part of the 

 "Astian" series (Pliocene proper of (.Japellini), have been shown by 

 Foresti to hold about 80 percent of living forms, reducing, therefore, 

 the faunal peculiarity, in its lowest expression, to 20 per cent. On 

 the other hand, the deposits immediately underlying these, forming 

 still apart of the true Pliocene series Foresti's horizon III hold 

 barely more than 43 per cent of living forms, and are thus strongly 

 individualized by their faunal peculiarity, in so far, at least, as a 

 relationship with the overlying deposits is concerned, although 

 the ties with the deposits underlying (Mio-Pliocene of Capellini- 

 Messinian of Mayer) are much more intimate. Horizon II of For- 

 esti is characterized by some 39 per cent of living forms, and I by 

 nearly 31 per cent ; both of these divisions are by many Italian 

 geologists classed with the Miocene, which really appears to be their 

 true position, contrary stratigraphical evidence notwithstanding. 



Seeing how very closely the Pliocene fauna in its highest expres- 

 sion approximates the fauna of the present day (et conseq. the Post- 

 Pliocene fixuna), and the broad latitude of peculiarity allowed it by 

 most geologists, it becomes interesting to inquire in how far similar 



