TERTIARY AGE. 



501 



The above remarks on the animal life relate only to the Middle 

 Eocene and later species. The Lignitic beds, or Lower Eocene, of the 

 Rocky Mountain region and the Pacific Border are remarkable for 

 combining, along with species of a true Tertiary character, others that 

 are characteristically Cretaceous, owing to the fact that the Cretaceous 

 strata pass up without break or marked transition into the Lignitic 

 Tertiary. These Cretaceous and Cretaceous-like species include Ino- 



Figs. 908-913. 

 908.,^ 909 



912/ 



Lameuibranchs. —Figs. 908, 908 a, Corbula (Potamomya) mactriformis ; 909, Cyrene (Corbicula) 

 intermedia ; 910, Unio priscus. Gasteropods. —Fig. 911, Viviparus retusus ; 912, Melania Ne- 

 brascensis ; 913, Viviparus Leai. 



ceramics problematicus (Fig. 837, p. 461), and other allied species, which 

 occur at various levels, through thousands of feet of rock, and are 

 abundant in some beds. In California, an Ammonite continues to the 

 top of the Lignitic series. Another peculiarity, already alluded to, is 

 the abundance of fresh- water shells in some beds. Some of these 

 fresh-water species, from the upper Missouri region, are represented in 

 Figs. 908 to 913. 



II. Vertebrates. — The Laramie beds have not yet afforded any 

 remains of Mammals, and no Vertebrate remains excepting those of 

 Fishes and Reptiles. Saurians occur in it, related to the Dinosaurs ; 

 and this is the strong Cretaceous feature of the beds. 



1. Fishes. — The remains of Ganoid fishes, (genera Lepidosteus, 

 Amia), and Teliosts (Clupea), are abundant in the Green River 

 shales, which underlie the Bridger beds, along with remains of Plants 

 and Insects ; and a few teeth of Sharks have been found in the New 

 Mexico Eocene. The Marine Tertiary beds of the Gulf and Atlantic 

 border, and especially of the Eocene, contain, in many places, shark's 

 teeth in great numbers ; three kinds are represented in the accompany- 

 ing figures. Some of the triangular teeth of Carcharodon megalodon 

 Ag. (resembling Fig. 914), are 6 inches broad at base and 6J long. 



2. Reptiles. — Species of Crocodiles (among them, Crocodilus Elli- 

 ottii Leidy, from South Carolina), of Snakes (of genus Dinophis Marsh, 

 from New Jersey, Boavus and Lithophis, from Fort Bridger), some 

 twenty feet long, and of Turtles (several species of Testudo, Emys, 

 etc.), from the Atlantic border and the Rocky Mountain region. 



