44 GEOLOGY OF THE DENVER BASIN. 



surface, which, combined with the effects of the erosion of the Platte aud 

 its predecessors, lias produced the eastern rim of the Denver Basin. The 

 amount of arching- is not readily determinable, since it does not come under 

 direct observation. It would be greater or less according to whether, on 

 the one hand, at this distance from the original shore-line there is already a 

 considerable thinning of the strata or, on the other hand, the arching is 

 within the limits of what students of orographical geology have called the 

 syncline of deposition, 1 which, as they assume, is produced by the extra 

 weight brought upon the sea-bottom by the greater thickness of beds 

 deposited along the shore-platform of a continent or continental island. 



In the present case, if there had been a syncline of deposition whose 

 eastern limb had a perceptible inclination to the west the subsequent 

 movements of compression would have produced an anticlinal fold of vis- 

 ible amount of arching along the limb, which is evidently not the case. 



On the other hand, it is to be remarked that, though the present 

 surface rises slightly from the Platte Valley eastward, if one takes into 

 consideration a longer distance eastward — say from the point nearest 

 the foothills where the strata assume a horizontal position to the eastern 

 boundary of Colorado — there is a general slope of the surface eastward, 

 which may be sufficient to account for the appearance of successively 

 lower beds of the horizontal formations, without having recourse to any 

 supposed arching of the strata or of the sea-bottom to produce a syncline 

 of deposition. The actual proof of the one fact or the other could 

 under these conditions he obtained only by the accurate determination 

 of the relative position of the bottom line of some formation or of an 

 easily recognizable bed within a formation at a number of different points. 

 Such a determination can hardly be hoped for under existing conditions. 

 It mar he assumed, then, as most probable that the existence of the 

 Denver Basin is due rather to erosion than to curving of the strata into a 

 low arch within a hundred miles from the mountains. It is probable that 

 the long-shore currents with a general northern direction, which, as has 

 already been shown, are proved to have existed in the Dakota Ocean as 

 well as in the Arapahoe and Denver lakes, may have produced a series of 



'Conditions of Appalachian faulting, B. Willis and C. W. Hayes: Am. Jour. Sci. (3), Vol. XLVI, 

 Oct., 1893, p. 257. 



