CONTENTS. 



Page 



Introductory 11 



History of Exploration • • • 16 



Geographical Distribution 20 



Classification and Correlation 22 



Nature of the Deposits • • 2 7 



The Chadron Formation • • 36 



The Brule Formation 38 



The Arikaree Formation 4° 



The Middle Miocene 43 



The Upper Miocene 44 



Concretions and Sand-Calcite Crystals 44 



Sandstone Dikes and Chalcedony Veins 46 



Geodes 5° 



Devils Corkscrews 5 1 



Manner of Deposition 53 



Source of Materials 58 



Geologic History 59 



Physiographic Development 61 



Economic Mineral Products 65 



Fossils 68 



Extinction, Evolution, Migration -. . 68 



Collecting and Mounting 71 



The Classification and Naming of Extinct Animals 72 



Carnivora 76 



Creodonta yy 



Canidae 78 



Felidae 81 



Mustelidae 84 



Insectivora 84 



Rodentia 86 



Ungulata (Herbivores) 88 



Perissodactvla 88 



