254 GEOLOGT2 OF THE DENVEK 1JASIN. 



The age of the Monument Creek is for the present considered 

 Miocene, on vertebrate paleontological evidence. 1 



LIFE. 



The life of the Monument ('reek, so far as known, lias been described 



b\ Professors Marsh and ("ope. It will not be discussed in this report, 



since the formation enters so little into the stratigraphy of the Denver 



Held. 



STRATIGRAPHICAL RELATIONS. 



The uneven and rolling Boor of the Miocene lake in which this 

 formation was deposited deserves special remark. Though changes in 

 level have probably taken place from time to time in the area constituting 

 the Denver field liv which certain areas of beds have Keen elevated and 

 others, perhaps, equally depressed, there is abundant evidence that erosion 

 also has played an important part in the early topography of the country, 

 in times prior to. the deposition of the Monument ('reek group. This fact 

 is brought out by the prominent hills and hollows which occur at the line 



of union between the Monument ('reek and underlying formations, and it 



is especially well dei istrated in the relations between the Laramie and 



the Monument Creek in the vicinuy of Scranton, and in those between the 



Denver and the Monument ('reek to the east and south of this. In the 



latter case, not only are bosses of the Denver formation found projecting 



through the Monument ( 'reek beds wherever a, favoring gulch has been cut 



sufficiently deep, but along the line of union generally there is a constantly 

 varying height in the pre-Miocene surface, the amount of variations at 



times reaching lot' to lot) feet. The most striking instance of erosion, 

 perhaps, must have occurred at the close of the period in which the 

 Denver formation was deposited, consisting of the removal, prior to the 

 deposition of the Monumenl ('reek, of an enormous amount of the older 



beds. This is evident from the difference in the topographic and geologic 

 horizons between the upper beds of the Denver, which appear in the 

 summit of Green Mountain, and those immediately underlying the Monu- 



ument Creek along the southern border of the field, the former being both 



topographically and geologically far above the latter. 



Prof. E. I >. < '"i"'' torn. Kept. U. S. Geol. and Geog. Sun <v of the Territories, Vol. VII, Colorado, 

 1*7:;. p. ISO. 



