180 A. C. Peak— Age of the Rocky Mountains in Colorado. 



Park Mr. Marvine found the Lower Tertiary and the underlying 

 Cretaceous conformable except at one point.* In southwestern 

 Colorado tiie Cretaceous and Tertiary appear to be cont. 

 while in the northwestern part of' the state the strata were 

 apparently conformable from the base of the Cretaceous to the 

 middle of the Miocene. This may be because of the distance 

 from the axis of elevation, the elevation not being sufficient to 

 lift the area above the sea-level at the end of the Lower Ter- 

 tiary. I have no evidence in any of my districts of any violent 

 action at the close of the Cretaceous. The apparent uncon- 

 fcies at Golden and near Colorado Springs I have already 

 explained. There are, however, evidences in some portions of 

 Colorado, of disturbance toward the close of the Cretaceous ; 

 but it is not until the end of the Lignitic Period that we find 

 evidences of a geological break, f There was probably, as indi- 

 cated by Hayden and Newberry, an elevation commVncinir in 

 early Tertiary time, for the marine deposits of the Tert'iarv 

 elianue gradually to fresh-water deposits as we ascend, but 

 there was no marked action until the close of the Lignitic. 

 There must have been a subsequent depression, for east of 

 South Park near Florissant, we find Miocene^ strata resting on 

 granite, with no older beds beneath,§ and on the Colorado 

 divide, the Miocene rests on the granite of the Front Range 

 and on the upturned edges of older strata. The lowest beas 

 here, also, were evidently made from the material derived from 

 the adjacent mountains. In Middle Park, Marvine found 

 Tertiary beds resting on the granites and on Cretaceous shales. 

 occupying all the lower basins. "Near the borders of these 

 show that their material was 

 from the adjacent rock, often being of coarse gran- 

 itic or schistose debris, or of the lignitic sandstones worked 



From what I have written, I think it is evident that in 

 at the close of the Carboniferous, instead of an eleva- 

 tion there was subsidence commencing at some period prior to the 

 close of the Carboniferous, and continuing throu»h the Triassic. 

 Jurassic, and Cretaceous into Tertiary time. C 



At the close of the Trias we have" no evidence of a second 

 epoch of elevation. The close of the Cretaceous was not 

 marked by violent disturbance. 



I agree with Prof. Stevenson that d 

 time there was great volcanic activity 



* Report U. S. Geol. Survey, 1873, p. 



+ Report IT. S r, ~' ° 



i By Miocene 



