The Tertiary Formations of i 



[March, 



— 



great depth, and the Puerco river be- 

 comes the receptacle of great quan- 

 tities of slimy looking mud. Its 

 unctuous appearance resembles 

 strongly soft soap, hence the name 

 Puerco, greasy. These soft marls 

 cover a belt of some miles in width, 

 jj and continue at the foot of another 

 g, line of sandstone bluffs, which 

 * bound the immediate valley of the 

 | Puerco to a point eighteen miles 

 « below Nacimiento. 

 S "The Puerco marls have their 

 principal development at this local- 

 ity. I examined them throughout 

 the forty miles of cutcrop which I 

 observed for fossil remains, but 

 succeeded in finding nothing but 

 fossil wood. This is abundant in 

 the region of the Gallinas, and in- 

 cludes silicified fragments of dicot- 

 yledonous and palm trees. On the 

 Puerco, portions of trunks and 

 limbs are strewn on the hills and 

 ravines, in some localities the mass 

 of fragments indicating the place 

 where some large tree had broken 

 up. At one point east of the river 

 I found the stump of a dicotyled- 

 onous tree which measured five feet 

 in diameter." 



The fauna of this formation is 

 different from that of the other 

 Eocenes in the presence of a sau- 

 rian, Champsosaurus, which is char- 

 acteristic of the Laramie Cretaceous, 

 and a marsupial Mammal (Ptilodus) 

 which is a remnant of a type only 

 known otherwise from the Juras- 

 sic. Its characteristic genera are 

 Catathlczus, a many-toed hoofed 

 animal, Psittacotherium, a gnawing 

 Tillodont, and various flesh-eaters 

 with primitive teeth. Coryphodon 



