256 GEOLOGY OF THE DENVER BASIN. 



between its surface phenomena and those which may be definitely connected 

 with the Glacial period. They will therefore be described independently 

 and by themselves, with no attempt at correlation with similar phenomena 

 in outside regions beyond the indication of certain lines of investigation 

 that may be profitably followed by those who in future time may under- 

 take to establish systematic connection between the Pleistocene phenomena 

 observed in the various regions west of the Mississippi and Missouri valleys 



The descriptions given below, while specially applicable to the area 

 represented on the Denver atlas sheet, hold good in a general way for a 

 large portion of the plains area of eastern Colorado, reconnaissances having 

 been made for the purposes of this investigation over the portions of this 

 belt adjoining the various railroad lines from Cheyenne southward to the 

 Arkansas Valley. 



The period during which the geological events outlined here occurred 

 may be divided into an earlier and a later erosion epoch, with an interme- 

 diate epoch of deposition, which mav be termed, from the character of its 

 most important deposit, the loessial epoch. 



HAULIER EROSION EPOCH. 



To what extent the topographical features produced during this epoch 

 had already been outlined by erosion during Tertiary time, or prior to the 

 Glacial period, there is now, so far as known, no means of determining-. 

 The latest Tertiary formation observed in this area, the Monument Creek 

 beds, reached the foothills of the range at a level which is now between 

 7,500 and 8,000 feet above sea-level, and the original upper surface of the 

 Denver beds was probably a few hundred feet lower, their present greatest 

 elevation at the top of Green Mountain being about 7,000 feet. No recent 

 conglomerate has been recognized which can surely be correlated with that 

 often found along the mountain flanks overtopping all Tertiary beds, and 

 which, from analogy with its best-defined representative at present known, 

 the Wyoming or Bishops Mountain conglomerate of the Uinta Mountains, 

 may he assumed to have been formed previous to the greatest extension of 

 the ice of the ( irlacial period. ( >n the other hand, opposite to Green Moun- 

 tain there is evidence of a former peneplain at about 7,500 feet extending 



