398 GEOLOGY OF THE DENVER BASIN. 



of the basal sandstone of the Laramie. The line of division between the 

 two formations is marked by a strongly developed bed of the fossils 

 characteristic of this horizon. The Fox Hills sandstone is divided into an 

 upper and lower bench, both quarried and used in constantly increasing 

 amounts in the construction of residences and office buildings in Denver. 

 The upper bench is the familiar yellow sandstone, everywhere tin- cap 

 of the formation. The lower is a bluish-gray sandstone, in texture much 

 finer than the upper. Both sandstones are aggregates of quartz grains 

 with mica or some other mineral in minute quantities. The bluish stone 

 contains more clayey matter than the yellow, and in places is inclined to a 

 shah" structure; below, it shades into the general mass of arenaceous shales 

 composing the bulk of the formation. Other differences between the upper 

 and lower sandstones are, greater quantity of iron oxide in the upper, to 

 which it owes its yellow color; the comparative freedom of the lower from 

 this salt, but the presence of an appreciable quantity of lime, producing 

 hard nodular masses of calcareous sand, from 2 to 3 feet in diameter. 

 Both benches, but more frequently the upper, show a few scattered fossils; 

 the casts are not sufficiently numerous, however, to render the stone 

 undesirable, although they must be considered in its selection. The I km Is 

 occupy an approximately horizontal position, are crossed by few joints, 

 and from their massive character may be quarried in any desired size. 

 Tlie upper sandstone is, indeed, a single bed, from 15 to 20 feet thick ; the 

 lower usually occurs in lifts of <> or 8 feet, but may be still further divided, 

 locally, by bands of shaly structure. The ratio of absorption has not 

 been well determined for these sandstones, but it is somewhat higher than 

 for those of Triassic age. Of the two varieties afforded by the Longmont 

 quarry, the blue is stated by the quarrymen to be perceptibly more 

 absorbent than the yellow. Both varieties are porous and in the dry 

 atmosphere of the West quickly yield up their quarry water after removal 

 from their beds They are said not to reabsorb moisture to a detrimental 

 degree after once having been seasoned. Quarrying is not carried on in 

 the winter months. The yellow stone is used for residences and for tall 

 business structures, but the blue is probably adapted for residences only. 



