ENVIRONMENT OF THE TITANOTHERES 



103 



7. Near Dickinson, S. Dak. (Douglass) 40-50 



8. Pine Ridge, S. Dak. (Darton) 30-60 



9. Beaver Divide, Wyo. (Granger) 



10. Bates Hole, Natrona County, Wyo 



11. Adelia, Sioux County, Nebr. (Darton), about 



Between Platte River and Arkansas River drainage 



(Darton). ("Monument Creek group" 

 of Hayden; Castle Rock conglomerate 



of Richardson, 1912.1) 300 



Horsetail Creek, northeastern Colorado 

 (Matthew,1901.1), not over 



46 



(?) 



12. 



13 



between the upper fauna (now unknown) of Uinta C 

 and the fauna of the lower levels (Chadron A) of the 

 White River group. The passage from Eocene to 

 Oligocene time probably occurs within the period of 

 deposition of Uinta C. Scott is disposed to put all of 

 Uinta C in the Oligocene. 



General Section of the Tertiary rocks of Nebraska. 



100 



The deposits at these localities, some of 

 them indicated on the accompanying map, 

 represent only the exposed parts of the lower 

 Oligocene deposits of the great flood-plain sys- 

 tem now known as the Chadron and corre- 

 lated formations, the larger part of which is 

 covered by the Brule and Arikaree formations. 

 This flood plain extends 325 miles north and 

 south and 300 miles east and west. We do 

 not know whether it was wholly continuous. 

 Such an area would embrace 97,500 square 

 miles, which would not exceed the present 

 Andean flood plains. 



At the base of these sediments in South Da- 

 kota and northern Colorado there are abundant 

 remains of titanotheres, certain of which are 

 in stages of evolution no more advanced than 

 those found at the base of Uinta C, Diplacodon 

 zone. Consequently the faunistic relation be- 

 tween the titanotheres living in the mountain 

 basins and those living on the Plains remains 

 to be solved by future discovery. This rela- 

 tion may be revealed in the "missing" faunal 

 zone. At present we may divide the life zones, 

 in descending order, as follows: 



17. Titanotherium zone: 



Chadron C, levels 3, 2, 1: 

 Brontops robustus. 

 Menodus giganteus. 

 Brontotherium platyceras. 

 Chadron B: 



Brontops dispar. 

 Menodus trigonoceras. 

 Brontotherium hatched. 

 Chadron A, levels 1, 2, 3: 



Brontops brachycephalus. 

 Menodus heloceras. 

 Brontotherium leidyi. 

 16. Theoretic zone of Uinta C (upper levels, or Uinta 



C 2): Unknown or "missing." 

 15. Diplacodon zone of Uinta C (lower levels, or Uinta C 1) : 

 Protitanotherium emarginatum. 

 P. superbum. 

 Diplacodon elatus. 



It is very important to recall the fact that 

 titanotheres have thus far been determined from only 

 the lower 100 feet of Uinta C, that they are only 

 partly known, and that when fully known we shall 

 probably find a close generic if not specific correlation 



Figure 70. — Facsimile of the Meek and Hayden Tertiary section of 1862, 

 showing original definitions of White River group and Wind River 

 formation 



The deposits are now known to include the following: 



"Loup River beds" (lower Pleistocene fauna listed). The area includes deposits of the Plio- 

 cene and Miocene (Ogalalla formation of Darton). 



"White River group," including lower Miocene (Arilcaree formation of Darton) and Oli- 

 gocene (Brule and Chadron formations of Darton). The " Clioeropotamus" is Ancodus 

 amcricoKKs.the ancodont of the Chadron formation (Titanotherium zone). 



"Wind River deposits" (summit of the lower Eocene). 



"Fort Union or Great Lignite group" (basal Eocene). 



OLIGOCENE FLOOD-PLAIN SEDIMENTATION IN THE 



WESTERN GREAT PLAINS REGION 



CONDITIONS OF DEPOSITION 



A very long period of extremely slow sedimentation, 

 east of the Rocky Mountains of Wyoming and Colo- 

 rado, began in lower Oligocene time and extended 

 without interruption to lower Miocene time, laying 

 down the great deposits originally described as the 

 White River group by Meek and Hayden (1862.1, 

 p. 433) in the following language: 



