424 GEOLOGY OF THE DENVER BASIN. 



been passed without comment in the search for greater yields. The value 

 of their record, however, is established in such instances as are given, for 

 not only is a greater persistency thus indicated for the flow, but the actual 

 water-bearing character of the zone is preserved. A How nonutilized in 

 one locality or well may become of importance in another either through 

 natural increase or through the diminution of other flows in this particular 

 region. Examples of but two distinct flows, from different layers in the 

 same water-bearing zone, either the lower or upper, are also not infrequent; 

 in the vertical interval, however, at other localities, several flows may be 

 recorded. This is in harmony with the distribution of the materials con- 

 stituting the water-bearing zones, which is not everywhere uniform; the 

 materials may vary laterally from an open, porous bed of sand or con- 

 glomerate to one of much closer texture, almost impermeable to water, or, 

 at least, by difference in texture and porosity, affording an easier channel 

 in one direction than in another. 



The upper and lower water-bearing zones of the Arapahoe formation 

 are separated by a more or less clearly defined body of shales of a general 

 thickness of about 130 feet. Occasionally the lower zone shows a tendency 

 toward an upward extension, while the upper one has here and there a flow 

 slightly below its average lower limit. Within the median zone there 

 are Locally developed beds of a more or less arenaceous composition, 

 which yield excellent flows to the scattered wells tapping them, and which 

 apparently constitute an almost continuous water-bearing body beneath 

 the lower or northern portion of the city, from Twenty-sixth street to the 

 Grant smelter, and, again, in the vicinity of Argo. Considering the field 

 as a whole, the midde zone may be regarded as in a measure blending 

 the more highly developed upper and lower water-bearing series of the 

 Arapahoe. 



Of the wells deriving their flows from the Laramie, the Evans is of 

 particular interest as having alone reached in depth the upper portion of 

 the coal series at the base of the formation. The details of this well are 

 given in the chapter on individual wells. The other wells of the Laramie 

 air sunk only to locally developed water strata in the clays of the upper 

 member. 



