THE MIOCENE OF EUROPE, ASIA, AND NORTH AMERICA 281 



upper IMissouri east of the Rockies above the region of Helena, especially 

 the Gallatin, Madison, Jefferson, Beaverhead, Ruby, Big Hole, Hell 

 Gate; they extend also along the Bitter Root rivers and their tributaries. 

 Hayden and Peale in 1871 and 1872 gave the first good general description 

 of these deposits in the Annual Reports of the United States Geological 

 Survey of the Territories. 



The geologic history of these successive formations differs in one im- 

 portant respect from that of the great plains of Nebraska and South Dakota, 

 because the older Oligocene beds were uplifted in places to a considerable 

 angle (35°) before the Middle Miocene deposits were laid do^^^l. Exten- 

 sive layers of volcanic ash overlie the lower Oligocene beds of the Titano- 

 therium Zone, and the Upper Miocene Madison Valley Formation is partly 

 composed of layers of volcanic ash as well as the 'channel beds' of sand 

 and gravel. 



Pipestone Creek. — The oldest mammals of these deposits are those 

 found in the lower beds near the three forks of the Missouri River, on 

 Pipestone Creek near Whitehall and on the Big Hole north of Dillon. 

 These beds consist of gray and yellow clays and sandstones and conglomer- 

 ates, 200 feet in thickness, containing a lower ' Titanotherium Zone' fauna, 

 namely, of Lower Oligocene age. 



Deep River. — Near White Sulphur Springs, also, in the valley of Deep 

 River, there is a comparatively small lacustrine or flood plain deposit, in- 

 cluding the 'Lower' and 'Upper' Deep River beds. The 'Lower Deep 

 River beds' contain a fauna of Upper Oligocene age. The prevailing 

 fauna of the overlying, or 'Upper Deep River beds,' which has been de- 

 scribed by Cope (1879) and Scott (1893, 1895) is of Middle Miocene age; 

 this is the typical 'Ticholeptus Zone' of Cope. Here we find remains of 

 brachyodont and subhypsodont horses, and of the oreodonts (Merychyus 

 and Ticholeptus). According to Cope, the Trilophodon. among the earliest 

 Proboscidea occurring in America, is found here ; Douglass thinks it possible 

 that this type belongs to a more recent formation. 



Flint Creek. — Subsequent in age to these three faunas are the mammals 

 of Middle Miocene age contained on Flint Creek and in the lower portion 

 of the valley of the Madison River which united with the Jefferson and 

 Gallatin to form the Missouri. 



Madison Valley. — This formation, of true Upper Miocene age, two 

 hundred and fifty feet in thickness, is composed of sands, gravels, clays, 

 and volcanic ash that are often grassed over, covered with drift, or entirely 

 washed away; yet near the Madison River there is one exposure fifteen to 

 twenty miles in extent. It contains hypsodont horses (Protohippus and 

 N eohipparion) , the camel Procamelus, the primitive deer BlasUymeryx, also 

 trilophodont mastodons. Especially important is the ruminant obtained 

 here, originally described by Douglass as Palceomeryx, but now referred to 

 Dromomeryx. 



