THE OVEBLAKB I^OUTE COUXCIL BLUFFS TO OGDEK. 



39 



The stations Corlett and Borie are passed between Cheyenne and 



Otto. 



views 



Range of the Rocky Mountains may be obtained to the left (sotith). 



Otto- 

 Elevation 6,946 feet. 

 Omaha 530 miles. 



plainly 



the moi 



massive and scarcely less elevated mountains north 

 of it. Toward the right (north) the foothills east of 



form 



plainly visible from the train. They consist of 

 upturned to a nearly vertical position. These rocks 



sediment 



range m age 



The Oligocene formations are 



family and seem to have been confined 

 almost entirely to North America. Their 

 remains are the most numerous and con- 

 ppicuons fossils found in the lower Oligo- 

 cene beds in western America. They 

 were clumsy brutes of elephantine size 

 having on the front of the skull a pair of 

 great bony protuberances, which although 

 hornlike in form were probably not 

 sheathed in horn. (See PI. VII, D, p. 41.) 

 The head was long and large and of fan- 

 tastic shape. In its thick heavy body 

 and short, massive legs the titanothere 

 resembled the modern rhinoceros. It 

 was doubtless a sluggish, stupid beast, for 

 its brain was small in comparison with the 

 cene time and the divides between the j size of its body. The brain ca\ity was 



systems . 



among tlie most widespread and most 

 regularly distributed of the Tertiary for- 

 mations of the Great Plains and cover a 

 vast area in Nebraska and Wyoming. 

 The sediments composing them were 

 deposited by streams that meandered over 

 low-lying plains and slowly built ui> the 

 surface, much as the lower Mississippi is 

 now building its delta or the Platte its 

 flood plain, over which the train has just 



passed. Some of the old stream channels 

 can be recognized by the filling of con- 

 solidated sand and gravel. 



The plains country of Nebraska and 

 eastern Wyoming was low during Oligo- 



streams were not high enough to prevent 

 flooding during high water. The whole 

 country was virtually a great flood plain 

 on which accnmulated the sediments 

 that the rivers brought from the moun- 

 tains. With these sediments occur beds 

 of pure volcanic ash, which must have 

 been carried by the wind or floated by the 

 streams for long distances. The volca- 

 noes that had been so active in western 

 America during the Eocene epoch had not 

 cea*sed their eruptions — indeed, they have 

 not yet become entirely extinct, as is tes- 

 tified by the recent outburst of Laiisen 

 Prak, in northern California, although 

 throughout later Tertiary and Quaternary 

 time their fires have been gradually going 



out. 



lower Oligocene or Chadrou forma- 



rri 



rii 



< 



tion is often called the Titanotherium 

 beds because it contains bones of extinct 

 mammals of that name. The titano- 

 therca termed a Comparatively short-lived 



only a few inches in diameter and was 

 surrounded by thick bone, as if to with- 

 stand shocks in battle. The titanotheres 

 were the most formidable animals of the 

 time, and though, so far as known, there 

 were then no carnivores capable of doing 

 them serious harm, yet they seem to have 

 disappeared suddenly from North Amer- 

 ica, Their bones are not found in strata 

 above a certain geologic horizon. The 

 disappearance of a race of animals from 

 any locality or even from the face of the 

 earth does not neceeearily require a long 

 period of time. It is easily conceivable 

 that the titanotheres were exterminated 

 by some disease or that one of the physical 

 changes which were so common in the 

 West during Tertiary time made their Life 

 conditions here unfavorable and drove 

 them to some other region, in which their 

 remains have not yet been discovered. 



The animals of Oligocene time seem to 

 have been abundant as well as varied in 



