TERTIARY MAMMAL HORIZONS. 9 



Trouessart's ('97) Catalogiis would have been far more val- 

 uable if localities had been cited as well as the geological 

 divisions. 



The first step is to ascertain how far the Periods or Systcmcs 

 can be paralleled in America and Europe and similar permanent 

 limits placed between them. The second is to establish, as con- 

 venient divisions of each, Upper, Middle, Lon'cr, or Lcnocr and 

 Basal. It is not too much to hope that the synchronism of 

 these periods in the entire Holarctic region during the Tertiary 

 can be established with considerable exactness. The Stages and 

 Substages present much greater difficulty and may prove impos- 

 sible owing to the absolute independence of the earth move- 

 ments which caused them in the old and new worlds. It is 

 perfectly e\'ident that the overlapping of these deposition stages 

 would be the rule and that exact synchronism would be largely 

 coincidence and therefore highly improbable. All that we can 

 reasonably hope to establish in the near future is an approximate 

 parallelism of the Stages ; ultimately the lines of overlap may 

 be determined. 



III. COMPARISON OF THE EOCENE IN EUROPE AND 



AMERICA 

 1. The Puerco without a Faunal Parallel 



The base of the American Eocene is the Puereo, which has 

 been observed by Cope and Wortman to immediately overlie 

 the upper Cretaceous in northern New Mexico. 



Contrary to the prevailing opinion and usage there is in Eu- 

 rope no known fossil mammal deposit parallel to the basal 

 Eocene or Puerco of America. The Puerco fauna proper is 

 older than the oldest in Europe. 



We may therefore provisionally conclude that the fresh water 

 Puerco deposits were approximately of the same age as the 

 earliest marine and brackish limestones of the Suessonien Sea, 

 namely, the Montien (Calcaire grossier de Mons, Belgium), or 

 marls, Heersien, [Mariies de Heejs), Maitdiinien {Mariics de 

 Meiidoii), all resting unconformably on the Cretaceous. 



