ARTESIAN WELLS. 407 



Fox Hills sandstone, immediately beneath, form a water-bearing zone of 

 nearly 200 feet The remaining sandstones in the lower Laramie occur at 

 short intervals within the succeeding 50 feet; they are between 5 and 10 

 feet thick, and are interbedded with days, lignitic shales, and coal. Except 

 on the confines of the field the foregoing strata have not been pierced in 

 the exploitations for artesian water, unless in a single instance, in some of 

 their upper layers, in one of the deepest wells in Denver. 



The Fox Hills and lower Laramie sandstones may lie regarded as a 

 single water-bearing zone confined between two great bodies of impervious 

 clays, those of the Montana below ami of the upper Laramie above. It is 

 the lowest practicable artesian zone in the Denver Basin. 



The conglomerates and sandstones at the base of the Arapahoe. Tile Arapahoe formation 



supplies the greater part of the artesian water of the Denver Basin. The 

 heavy bed of conglomerate and sandstone at its base is doubtless persistent 

 beneath the entire area occupied by the formation: wherever it outcrops 

 or has been pierced its thickness has never been found less than 25 feet 

 often approaching 200 feet, and occasionally attaining even a higher figure. 

 It consists of the debris of the older sedimentary and crystalline rocks. 

 The sandstone is coarse-grained and the texture is therefore open. It is 

 the most pervious of all the strata underlying- the Denver held. 



The upper body of sands. This lieS frOUl 200 tO 350 feet below the SUmillit 



of the Arapahoe. It passes gradually into the arenaceous shales above, 

 but from those below it is somewhat more sharply defined. Locally, 

 however, it may extend quite to the lower sandstones. The material of 

 the upper sands is quartz, of a smaller grain than the basal members. 

 There is also a small percentage of (day either distributed through the 

 sands or as interbedded layers which split the zone into several minor 

 divisions. Along the outcrop of the formation bordering the foothills, 

 owing to the comparative fineness of its materials, the existence of the 

 upper zone is not so clearly shown as that of the lower. 



The shales of the Arapahoe. — Theseai'e arenaceous, with a percentage of clay 

 that is variable, but usually too great for the free passage of water. It is 

 doubtful, however, that any portion of them is absolutely impervious. 

 That there are definite Hows is probably due rather to a difference in the 



