148 GEOLOGY OF THE DENVER BASIN. 



of the lowest Laramie beneath the surface might possibly be reduced to 

 1,200 feet. 



The Arapahoe on the line of Section IV appears only among the 

 highly inclined series of beds adjoining the foothills. It there sinks a 

 considerable distance beneath the surface of the prairie, to be again brought 

 by erosion of the overlying beds within easy reach in artesian boring in the 

 valley of the Platte and its immediate tributaries. At the mouth of Cherry 

 Creek the formation is approximately horizontal, its base lying between 

 7<><» and 800 feet beneath the river. The formation has a general easterly 

 dip of about 2° between the foothills and the Platte, and at its eastern limit 

 may or may not again be bent slightly upward as the eastern rim of a 

 synclinal basin. The flexure suggested here is in no way necessary to the 

 success of artesian flows in the Platte Valley, since from lying upon and 

 against the west-sloping surface of the Laramie clays it there meets with a 

 most effective confining medium. The precise eastern limit of the Arapahoe 

 on the line of Section IV is conjectural, but its position in the section is at 

 least as far to the cast as drawn, its presence west of tins being everywhere 

 recognized in the deep artesian borings. 



In the eastern half of Section V a pronounced flexure has been given 

 the strata for reasons already stated. The depth at which the base of the 

 Laramie has been drawn at the eastern end of the section is 1,500 feet, or 

 about that of the other sections, indicating that the rise figured has taken 

 place chiefly between Sections IV and V, with its incipient point, perhaps, 

 slightly north of the line of Section IV. Conjectures as to underground 

 stratigraphy and structure are always unsatisfactory: it is necessary to 

 recollect that for the Denver Held the base of the Laramie is probably 

 rolling and that the foregoing figures are only approximate, and may vary 

 even "_'<»() or 300 feet, according to locality. 



The subterranean limits of the Arapahoe and its relations to the other 

 formations are indeterminable, except through the aid of numerous and 

 Systematic borings. From Sand ('reek southward the eastern edge of the 

 formation is totally obscured, and in the sections it has been drawn from its 

 recognized presence in deep wells in the Platte Valley, in the southeastern 

 portion of the city of Denver, and at an occasional point on the plains east 

 of I >enver. 



