the Cretaceous-Tertiary Problem. 219 



but must be due to migration. The same relations hold 

 partly true in the sub-Wasatch beds of the Bighorn 

 basin in Wyoming, Clark Fork Beds, and in the Cernay- 

 sian-Sparnacian succession of France. A new fauna, 

 practically identical in Europe and North America, sud- 

 denly displaces in the record an old one which had 

 endured for a long time, gradually evolving in loco. This 

 new fauna then undergoes the same process separately 

 in the two continents, of gradual evolution in loco, 

 throughout the Eocene, when another great migration 

 imposes a new and at first identical fauna in Europe and 

 America, to be evolved and differentiated through the 

 Oligocene. 



Above the Tiffany horizon comes the true Lower 

 Eocene with the well known ^^ Wasatch Fauna'' every- 

 where characterized, in Montana, Wyoming, Utah, Colo- 

 rado, New Mexico, as in France and England, by 

 Eohip,pus {^=Hyracotherium) , Phenacodus, Coryphodon, 

 PachycBfia, etc. 



The Alberta succession, commencing with the Belly 

 Eiver = Pierre :^= Upper Senonian, is followed by the 

 upper Pierre, then the Edmonton, and this by the Pas- 

 kapoo, formations separated by unconformities of no 

 very marked character. The Edmonton contains a large 

 fauna of dinosaurs and other Reptilia, including the 

 same groups and phyla as the Belly River fauna below 

 and the Lance fauna of later age, in an intermediate stage 

 of evolution. No mammals have been found in the 

 Edmonton. The Paskapoo contains no dinosaurs but a 

 small fauna of mammals, the major part identical with 

 those of the Lance, but including also a number of archaic 

 placentals, which are not found in the Lance and may be 

 identical with Fort Union mammals, although exact com- 

 parisons have not yet been made. They compare less 

 closely with the Torrejon fauna, and I have seen nothing 

 in them characteristic of the Puerco. This Paskapoo 

 fauna is extremely interesting but too fragmentary for 

 any more than provisional conclusions. So far as it 

 goes, it suggests correlation with the Lance or Fort Union 

 or something between the two ; some obscure difference 

 of facies may account for the absence of dinosaurs and 

 the presence of two mammal faunas elsewhere distinct. 

 It tends to confirm the palseobotanists ' insistence on the 

 near relation of Lance and Fort Union, for which I have 



Am. Jour. Sci. — Fifth Series, Vol. II, No. 10. — October, 1921. 

 15 



