156 GEOLOGY AND MINIXCJ INDUSTRY OF LEADVILLE. 



division of the Weber Grits formation, viz, the fossihferous and more calea- 

 reons and argillaceous beds at its base. The thickness represented is some- 

 what greater than that observed in other sections; but the upper limits of 

 the division are in themselv^es somewhat ill-defined, and the measurements 

 obtained here are uncertain, owing to the fact that they were not observed 

 in a continuous series of outcrops and certain beds mav have been redupli- 

 cated. 



From here eastward to the fault the outcrops are those of the ordinary 

 Weber Grits, coarse white sandstone predominating, with development of 

 micaceous sandstones passing into shales, occasional thin seams of carbo- 

 naceous shales, and a limited development of limestone beds Variation in 

 the strike is noticed fi-om N. 28° W., about midwav in the series, to N. ^° 

 W., near the fault. The latter direction corresponds more nearly with the 

 average strike of the beds near the fault, and the former may be considered 

 to be a bowing out of the strata, cau.sed by the intrusion of the large masses 

 of porphyry at White Ridge and Gemini Peaks. 



The actual foult plane is apparently exposed by a prospect hole on the 

 low saddle overlooking the gulch, where the contact of a dense quartzite, 

 in vertical position, with White Porphyry on the east, shows very marked 

 slickensides surfaces and a clay seam. A little to the west of this point is 

 a second contact of quartzite and White Porphyry, dipping 50° east. This 

 White Porphyry mav very likely be an intrusion in the beds of the Upper 

 Coal Measure formation, as has already been assumed to be the case with ;i 

 corresponding bodv on Pennsylvania Hill. This assumption and the fact 

 that the thickness deduced from the angle of the dip and the transverse dis- 

 tance between this point and the liase of the series necessitates the existence 

 of a portion of the Upper Coal Measui'e beds, have been the reasons foi* their 

 indication on the map and sections, since time did not admit of a suffi- 

 ciently detailed examination to determine their existence on lithological and 

 paleontological grounds. White Porphyry is found on the opposite side 

 of the gulch, near the top of the Weber Grits formation, as will be shown 

 later. 



Directlv east of the faidt, which occupies a saddle in the ridge, is a con- 



