58 A GEOLOGICAI, SUEVET OF LA^DS 



decayed stratum which may be seen in the banks of Indian creek 

 near its mouth. Above Ames's ranch another porous stratum 

 forms the exit of a large number of springs known as the Cold 

 springs. This stratum lies about 400 feet below the top of the 

 formation, and it is the most important water bearing horizon in 

 the formation. 



Mineral Occurrences. 



Mineral occurrences in these limestones are nowhere of much 

 consequence and not frequent. Calcite is occasionally found in 

 veins and cavernous pockets. The latter vary in size from a few 

 inches to considerable masses, which are apparently associated 

 with springs and ancient caverns. Several small veins were noted 

 on survey 24, near the springs in the base of the cliff on the east 

 side of Devil's river, about two miles east of .the mouth of Satan's 

 creek. It consists of columnar calcite crystals and averages about 

 three iuches in thickness. Another occurrence was noted just 

 north of the Twin Water holes, about half a mile west of the 

 centre of survey 33, in block A. The north bluff of Evans creek 

 at this place exhibits a synclinal fold which is clearly due to sett- 

 ling of the overlying strata, consisting of the Buda limestone, 

 into a cavernous hollow below. In the limestone on the slope of 

 this bluff there was a vein of calcite not exceeding six inches in 

 thickness. Its course is from east to west. The limestone cor- 

 responds to the Georgetown, and it is overlain by the DelEio clay. 

 Along the contact of these two formations pocket -like aggregates 

 of calcite lie in the limestone, and these are stained by infiltrated 

 ferruginous materials. An analysis of several samples disclosed 

 no trace of any valuable ore. 



In the lower hundred feet of the formation we find siliceous 

 material gathered into concretionary lenses and .sheets, as chert 

 and flint. There are at least two horizons of chert exposed in the 

 canyon above Pafford's crossing. These occur in the lowermost 

 indurated ledges. On survey 80 in block D cherty seams lie about 

 fort}- feet above the river in the east foot of the bluff. This ledge 

 was seen at intervals for several miles to the north. Along the 

 wagon road leading doTNTi to the river in survey 1 .5 in block B, two 

 cherty seams were noted. One of these consisted of concretions 

 of somewhat irregular form. This lies only a few feet above the 



