180 D avion — Age of the Monument Greek Formation. 



bones have also been collected for me along the valley of 

 Cherry Creek, half way between Castle Rock and Elizabeth, 

 consisting mainly of bones of titanotherium. They were 

 obtained at many localities and all from the sandstones of the 

 upper member of the formation. A fragment of a lower jaw 

 of titanotherium was the most distinctive fossil obtained. It 

 was found in the upper beds, at Kaumpfer's ranch, 7 miles 

 southwest of Elizabeth. In Wild Cat Canyon, 6 miles west- 

 by-south of Elizabeth, were found fragments of a jaw and the 

 distal ends of a titanotherium tibia and humerus. Portions of 

 a lower jaw of hyracodon, apparently nebrasensis, were found 

 in a well at Anderson's place 6 miles south-southwest of Eliza- 

 beth, together with various turtle bones. All of this material 

 appears to have been obtained from the upper beds and it cor- 

 relates these beds with the Chadron formation of the White 

 River group, or Oligocene. No evidence was obtained as to 

 the age of the lower member, but the fullers earth, as before 

 mentioned, is similar to that which is so characteristic in other 

 areas. The presence of the unconformity between the upper 

 and lower members suggests that the latter may be of Wasatch 

 or Bridger age. The nearest locality to the Monument Creek 

 area, at which Oligocene deposits occur in eastern Colorado, is 

 in the vicinity of Akron and Fremont's Butte, where titano- 

 therium remains occur in abundance. Farther north, in the 

 region about Pawnee Buttes, there are well-known localities 

 of the titanotherium and overlying beds. In the low inter- 

 vening area, east and southeast of Denver, Oligocene deposits" 

 are absent, but it is probable that originally they extended con- 

 tinously from the vicinity of Akron to the foot of the Rocky 

 Mountains in the Monument Creek area. There is much evi- 

 dence throughout the Great Plains region that the Oligocene 

 deposits were originally of wide extent, for outliers occur along 

 the mountain slopes and' in many widely separated areas. They 

 have been subjected to extensive degradation in Miocene, 

 Pliocene and later times and probably removed from large 

 districts, especially in the wider valleys. In my recent report 

 on the Great Plains,* there is given a map showing their pres- 

 ent distribution and probably former great extent. 



* United States Geological Survey, Professional Paper No. 32, pi. xliv. 



