218 W. D. Matthew — Fossil Vertebrates and 



Close above the Lance and Hell Creek lie the Fort 

 Union beds, devoid of dinosaurs, but not separated by 

 any stratig'raphic break, and containing a flora very 

 closely allied to that of the Lance and to the upper 

 Paleocene floras of Western Europe. A considerable 

 marmnal fauna has also been found in the Fort 

 Union, correlated, as above noted, with the better known 

 Torrejon fauna, or perhaps intermediate between this 

 and the Cernaysian, in any event Upper Paleocene. 



Li the San Juan Basin, Xew Mexico, the Puerco for- 

 mation overlies (unconformably) the Ojo Alamo=^ 

 Judith Eiver. It contains a large maromal fauna which 

 is wholly unkno^Ti elsewhere. Multituberculates form a 

 considerable element but the major part is archaic placen- 

 tals. There are no dinosaurs ; but the crocodiles, rhyn- 

 chocephalians and turtles are of the same groups as those 

 of the Judith and Lance, and not perceptibly more 

 advanced. The Torrejon overlies the Puerco conform- 

 ably, and contains the same and some additional fami- 

 lies of archaic mannnals, both multituberculates and 

 placentals. Some of the Puerco phyla can be fol- 

 lowed through, apparently as direct descendants, and in 

 these there is e^ddence of considerable evolutionary 

 change, representing a considerable lapse of time.^^ 



Over the Torrejon, unconformably, lies the Wasatch 

 group, of which the basal member is the Tiffany. This 

 is still faunally Paleocene, the mannnals archaic pla- 

 centals. The phyla that can be traced through show in 

 some instances a considerable advance beyond the Tor- 

 rejon, indicating considerable lapse of time, and are very 

 close to the succeeding Wasatch horizons of the true 

 Eocene. But in the Tiftany as in the Torrejon, the mod- 

 ernized placentals, abundant in the overlying horizons 

 of the Wasatch, are almost wholly absent. There is 

 betAveen Tiffany and true Eocene very little lapse of 

 time but a great change of fauna. For various reasons 

 impossible to present here I hold that the change is not 

 explainable as due in any degree to difference in facies, 



^^In the Puerco and also in the Torrejon, there are two distinct fossili- 

 ferous levels, and tlie collections from each of these show certain differences 

 in facies, but no evidence of lapse of time. Each formation is a faunal 

 unit, although differences of facies or accidents of sedimentation result in 

 different relative abundance of species in the different levels. This explana- 

 tion appears advisable in order to prevent any misunderstanding of typical 

 sections of these formations which have been published by Professor Osbom. 



