POST-DENVER MOVEMENT. 37 



ram-nus with that recognized in the above regions as the post-Bridger move- 

 ment, 1 since the only beds definitely determined to be of Eocene age which 

 lia\ c been found on the east flanks of the mountains, viz, those at Buerfano 

 Park, were upturned by this movement; or it may, on the other hand, have 

 been more nearly contemporaneous with those recognized in the Green 

 River Basin, prior to or following the deposition of the < rreen River Eocene. 8 

 It is evident that some dynamic movement took place during the Denver 

 period in connection with the outflows of basalt which formed the Table 

 Mountains, for the faulting of the Laramie and Fox Hills strata near Ral- 

 ston ('reek, opposite the main vent or fissure through which the basalt is 

 supposed to have been extra vasated. is evidently referable to the same 

 movement which produced this fissure. 



The faults which fracture the coal measures, and in one case the 

 Overlying Arapahoe beds, in the northern part of the Denver Basin area, 

 may also have heen determined by the shattering which accompanied this 

 volcanic eruption, especially if, as it is reasonable to assume, the eruption 

 of the Valmont dike in this region was contemporaneous with that of the 

 Table Mountain sheets. 



Whatever may have been the time in which the effects now recognized 

 as caused bv the post Denver movement wen- produced, whether it was a 

 single movement, or a succession of periodic movements, or an extremely 

 slow and long-continued movement, its character was peculiar and typical 

 of the foothill region in general, and will be specially considered under the 

 head of ••Structural geology." 



The erosion which followed the Denver movement was most extensive, 

 but here again it is difficult to differentiate that which properly belongs to 

 the period intervening between the deposition of the Denver and of the 

 next succeeding Monument Creek beds. In the center of the Denver Basin 

 something over 1,000 feet of the Denver strata have been removed up to 

 the present day. Under the edges of the Monument ('reek beds, on the 

 southeastern edge of the area mapped, about 600 to Too feel of Denver 

 beds probably remain, which, on the assumption that their original thick- 



1 R. C. Hills, Orographic and structural features of Rocky Mountain geologj : Proc. Colorado 

 Sci. Soc. Vol. Ill, p. 408. 



'Fortieth Parallel Reports, Vol. 11. Descriptive Geology, pp. 203-204. 



