GENERAL PRINCIPLES. 



261 



Pliohippus Beds. 



Pliokippus, Mastodon, Sag, etc. 



Miohippus Beds. 



Miohippus, XHceratherium, Thinohyus. 



Dreodon Beds. 



Edentates, Hycenodon, Hyracodon. 



Brontotherium Beds. 



Mesohippus, Menodus, Elotherium. 



Dakotah Group. 

 Coraanche Group. 



Tapir, Peccary, Bison, Llama. 

 Equus. Megatherium, Mylodm, Elephas. 



Diplacodon Beds. 



Epihippus, Amynodan. 



Dinoceras Beds. 



Tinoceras, Uintatherium, Idmnohyus, 

 Orohippus, ttelaletes, Colonoceras. 



Doryphodon Beds. 



Eohippus, Monkeys, CarniTores, Ungulates, Tillodonte, Rodents, Serpents. 



Lignite Series. 



Aadrosaurus, Dryptoaurus. 



Pteranodon Beds. 



Birds with Teeth, Hesperornis, IcMhyornis. 

 Pterodactyls, Pl( - 



Atlantosaurus Beds. 



Dinosaurs, Apatotaurus, AHosaurus, Nanosaurus. Turtles. IHplosaurus. 



Connecticut River Beds. 



First Mammals (Marsupials), (Dromatherium). 

 to, Amph: 



inosaur Foot-prints, Amphisaur 

 Crocodiles (Belodon). 



Permian . 



First Reptiles. 



Coal-Measures. 



Sub-carboniferous. 



First known Amphibians (Labyriuthodonts). 



Corniferous. 



Schoharie Grit. 



First Fish Fauna. 



Upper Silurian. 



First known Fishes. 



Lower Silurian. 



Primordial. 



Huronian. 



Lauren tian. 



No Vertebrates known. 



FIG. 164. Section of the earth's crust, to illustrate vertebrate life in America. 

 (Slightly modified from Marsh.)^ 



