384 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



Blue Limestone. — The Blue Limestoiie, as shown by the map, has an 

 unusually broad outcrop in California gulch, owing to erosion and to the 

 low angle at which it stands. From the bed of the gulch the outcrops extend 

 up along the hill slopes on either side, only obscured by slide or surface 

 ddbris, until cut off by the Iron and Dome faults, respectively. On the 

 Montgomery claim, a cliff exposure of a very considerable thickness of the 

 lower beds is afforded by an open cut, where the limestone was formerly 

 quarried as a flux for the smelters. There is also a small outcrop west of 

 the Emmet fault, near the bed of the gulch, below the Columbia tunnel. 

 From the upper beds in the Silver Wave ground were taken the specimens 

 illustrated in Plate VI (p. 64) and whose composition is shown in Appen- 

 dix B, Table V. The characteristic ribbed structure is here very well devel- 

 oped. The thickness of the formation, as calculated from these outcrops, 

 is two hundred feet or more, which is greater than that deduced from meas- 

 urements on Carbonate Hill. 



Silurian. — The White Limestone is disclosed in numerous prospect holes, 

 and some shafts on the south side of the gulch have cut the character- 

 istic Red-cast beds. The Parting Quartzite could not be unmistakably 

 recognized, owing to its close resemblance underground to decomposed 

 porphyry. There is, howeverj no reason to assume that it is wanting. 



Cambrian. — The Lower Quartzite is best shown in the Globe and Garden 

 City shafts, each of which has cut through it into the underlying Archean. 

 The quartzite is of the usual normal type and the Archean is a coarse- 

 grained granitoid gneiss. 



Iron fault. — The average direction of the line of the Iron fault is a little 

 east of north, but its course is very crooked, as shown on the map. Although 

 this irregularit}" may be somewhat increased by erosion, i. e , be greater than 

 if the line given on the map were its intersection with a horizontal plane, 

 still it cannot be considered abnormal, since from the bed of California 

 gulch northward to the Codfish Balls shaft it has been actually proved in 

 so many cases as to render its delineation unusually exact. 



It has been cut by the workings of the Garden City shaft; by the L. 

 M. shaft, which v.as sunk perpendicularly to the depth of two to three 



