164 GEOLOGY OF THE EUREKA DISTRICT. 



there an occasional elevation, seldom rising more than 100 feet above the 

 average height of the surrounding country. 



Over this entire area the only rocks which have been recognized are 

 the Upper Coal-measures, inclined toward the west at low angles agreeing 

 closely with the slope of the country. This prevents any considerable 

 thickness of strata being exposed, and it is doubtful if there can be seen 

 here a greater development of beds than those found south of Newark 

 Canyon, where it is estimated that 500 feet are shown in the ridge 

 which rises above the basaltic flows. At the latter locality the base of the 

 horizon is unquestionably exposed, but along the line of the Alpha fault 

 there is no structural evidence that the basal rocks come to the surface. 

 Almost anywhere" scattered through these limestones organic remains 

 characteristic of the Coal-measures may be found, but the most promising 

 field for collection is on the summit of the ridge just north of Garden 

 Canyon. Nearly all the forms obtained here are common enough elsewhere, 

 with the exception of Ptilodictya (Stenopera) carlonaria and P. serrata. Far 

 to the south of this latter locality, north of Weber Peak, and just above the 

 Alpha fault, occurs a nearly similar grouping without the latter two forms, 

 but with the addition of Macrodon tenuistruita. 



Perhaps the most important geological feature of this inclined table of 

 Upper Coal-measure limestone is the occurrence of an interstratified bed 

 of conglomerate varying in thickness from 15 to 20 feet. It is exposed in one 

 or two of the long ridges stretching out toward Diamond Valley, and in one 

 instance occupies a low depression on the top of the ridge. This conglomer- 

 ate is made up of pebbles of chert, jasper and quartz such as are found 

 throughout the Weber epoch, firmly cemented together into a hard sand- 

 stone. Mingled with these siliceous pebbles occur rounded fragments of 

 limestone carrying organic remains such a&Syringopora and Fttyilhta cylindrica 

 and other forms common to the Carboniferous limestones below the Weber 

 conglomerate, but in no instance are specific forms obtained other than those 

 previously recognized in the underlying limestones. This implies that after 

 the deposition of the lower portion of the Upper Coal-measures the country 

 underwent some slight changes in elevation, subjecting the Weber con- 

 glomerate and Lower Coal-measures to the influences of erosion, the mate- 



