412 GEOLOGY OF THE DENVER BASIN. 



therefore, as a confining stratum is variable. The deposit usually carries 

 an abundance of water, which may afford a copious or diminished yield, 

 according to the permeability of the underlying l>eds. 



Barriers effecting confinement of artesian water in the basin. Tile COnfig lira tioll ot the 



floor upon which the Arapahoe formation was laid down is ot' considerable 

 irregularity. This is clearly shown along the northwestern edge of the 

 younger formation, while on tin- eastern side of the held, in the region 

 of First and Second creeks, the upper Laramie clays appear to have 

 formed an ancient hill of considerable diameter, now laid bare of any 

 sediments that may have once formed a cap to it. North of this area 

 for some distance the Arapahoe still forms a thin overlying sheet, while 

 on the western and southern Hanks of the early Laramie eminence the 

 Arapahoe and Denver formations both occur in increasing- depth as 

 distance from the crest of the ancient hill is gained. 



-. <j, Sandstones of tin- Arapahoe; 6. clays of the Arapahoe; c, clays of the Laramie. 



The Denver formation, along the northwestern border of its area, 

 presents the same relations with the Arapahoe as exist on the eastern side 

 of the held between these formations and the Laramie. The Denver beds 

 rest against elevations of Arapahoe clays, the latter having formed hills 

 upon the Denver floor, as did the Laramie upon the Arapahoe floor. 



These relations between the three important water-bearing formations 

 of the Denver tield are shown in the general sections. 



It is apparent from the foregoing conditions that, while in part the 

 water is held in its basin by the introversal dip, it is also confined by 

 the harrier presented in the opposition to the water-bearing sands ot' the 

 Arapahoe and Denver ot' the strictly clayey strata of the Laramie. This 

 is illustrated in fig. 22, where the water-bearing sands, a, confined between 

 two impervious layers, /</', of the same formation are opposed at the line of 

 unconformity by clays of the older formation. 



