HORIZONS OF VERTEBKATE FOSSILS. 479 



Fragments of vertebrate remains, evidently of this same characteristic 

 fauna, have been found by the writer in the well-known rock columns of 

 Monument Park, south of Denver, and careful search there would doubt- 

 less bring to light well-preserved specimens. Farther to the south, and 

 also west of the mountains in the Wyoming Basin, typical fossils of this 

 horizon have been observed in place at various points. 



The horizon thus marked by the Ceratops fauna is indicated l>\ a 

 series of outcrops at various points along the eastern flank of the Rocky. 

 Mountains from Canada to New Mexico. From these exposures fossils of 

 this fauna have already been obtained at 15 different localities, although 

 systematic explorations have been made at only a few of the outcrops along 

 the line thus indicated. 



TERTIARY. 



The Eocene formation, which has such a greal development west of 

 the Rocky Mountains and is so rich in mammalian life, is apparently not 

 represented in the Denver Basin, nor indeed along the eastern side of the 

 mountains to the north. It is, however, well developed to the south in 

 Huerfano Park, and southwest, in New Mexico. 



BRONTOTHERIUM BEDS. 



The next higher horizon of the Tertiary, the Miocene, and the 

 succeeding Pliocene have an extensive development along the eastern 

 flank of the Rocky Mountains, and especially in the plains region. The 

 series of Lower Miocene fresh-water clays and sandstones which the writer 

 has called the Brontotherium beds form a well-marked horizon. They have 

 been recognized at various points from southeast of Denver, in Elbert 

 County, far to the north through Nebraska and Dakota, and have recently 

 been found in Canada. < hi the plains not far from Denver they have been 

 found, with their characteristic fossils, in depressions or pockets in the 

 underlying Ceratops beds, and this is the case, also, at various points in 

 the north, especially in Colorado and Wyoming, where the Brontotherium 

 beds have suffered great denudation. Farther east, in both Nebraska and 

 Dakota, these beds are overlain by other Miocene deposits of great 

 thickness, known as the Oreodon beds! Both series are well developed in 



